Site-wide links

Color Order FAQ

 

 

Do you have a question about color? Here is our current list of Frequently Asked Questions.

This page has been populated with questions submitted from around the world over the last decade. While we are no longer accepting new questions, we hope you enjoy reading the questions and answers here.

Other categories can be selected below:
Perception   |   Measurement   |   Imaging   |   Formulation   |   Color Order   |    Light & Matter

What percent of light is reflected from Brown beer bottle glass? Green beer bottle glass? Clear beer bottle glass?    (answer)

How does a flower´s color help it survive?    (answer)

We have a WWI aircraft we are recovering with fabric that requires a dark green paint for the wings. This aircraft is flown a lot and displayed to the public outside quite a bit. The problem is that this paint absorbs sunlight heat dramatically which reduces the life of the doped fabric, causing it to shrink prematurely and it is fairly expensive to replace. Would a primer coat of silver dope or white help reduce the absorption of the heat into the fabric under the dark green paint?    (answer)

I am looking for the differences between red, blue, green, and yellow dye. Can you tell me anything different about them, other than they are different colors?    (answer)

What part of the spectrum helps grass grow?    (answer)

Why does the color of a crayon or colored pencil look a different color on paper? For example, some purples show up blue on paper.    (answer)

Which light colors are absorbed by a yellow tulip?    (answer)

What colors (in order) would best absorb a green 529nm laser light?    (answer)

Are there established color values for the color of skin for various ethnic groups (like Lab or Munsell for example)? This is for a makeup manufacturer who wants to design packing for specific groups of people.    (answer)

I dyed 100% cotton red, yellow and blue and placed them in direct sunlight for a week. The red appeared to fade the most, but I can't explain why. Can you help?    (answer)

Why does red disappear when viewed behind red glass?    (answer)

Why can't humans see ultraviolet or infrared energy?    (answer)

What is the theoretical principals of the color change test in chemistry?    (answer)

Is color a quality in physics?    (answer)

I have noticed a couple of different species of early-flowering trees have pink blossoms which turn white literally overnight. It is the speed of the process which is intriguing. Do you know how it works?    (answer)

How can tulips be so many different colors when they are the same plant?    (answer)

How does chameleon paint (i.e. paint which color depends on viewing angle) work? What is its composition?    (answer)

Why does your hair change color during the season?    (answer)

Which minimizes solar heat absorption better, polished aluminium or white paint on it?    (answer)

Does the color of a laser affect the velocity of the light wave projected by the laser?    (answer)

What is the physics behind a blue-yellow polarizer such as the Singh-Ray Gold-N-Blue filter which photographers use to add yellow or blue highlights to polarized parts of a scene?    (answer)

When choosing an umbrella, what color is best to protect yourself from UV light?    (answer)

I would like to know if the color of the water (by adding food color dyes) will affect the absorption rate of water and thus the color of the white flower over time.    (answer)

Since a mirror reflects most of the light that falls on it, as does any white body, what is the difference between the two?    (answer)

I know that the color of a body depends upon the color that it reflects. What causes some bodies to be transparent, others translucent still others to be opaque?    (answer)

I am building a pit solar greenhouse and need to decide what color to paint the non-glazed walls. White would be the best for reflection onto the plants but I am also looking for more pleasing colors. What is the best color for growing plants?    (answer)

How do mood rings work?    (answer)

I understand that the visible spectrum is comprised of the wavelengths red, orange, yellow, green, blue, indigo and violet. Combined they make up white light. So does that mean that white is then a wavelength too? Do all the other colors/wavelengths add up to something that we recognize as white?    (answer)

Does the color of your hair affect it's ability to keep your head warm?    (answer)

Where do the beautiful colors of fireworks came from?    (answer)

What makes colors fade in plastics? What part or parts of the light spectum?    (answer)

How do paint colors affect the room temperature?    (answer)

Does a sheet of colored glass reflect, refract or absorb light? Or all 3?    (answer)

Does the color of glass effect the index of refraction?    (answer)

Why do colors abosorb and/or reflect heat?    (answer)

What makes wet grass greener than dry grass? A scientific explanation of more than just refractive index would be much appreciated.    (answer)

I am preparing a 3 band fluorecent lamp powder recipe for color point x=0.312, y=0.336, Ra= 82,SDCM<3. Can you provide any useful recipe development procedures, methods or any useful website for me about the color coordinates adjustment?    (answer)

I am shopping for a new motorcycle helmet and want to know the color's that would keep my head cooler in the sun. Where do colors such as grey or silver fit in as far as reflecting light/heat and staying cooler?    (answer)

Can you explain which coloured dyes change colour or fade and why when used as a gamma radiation dose indicator?    (answer)

Which colored paper reflects more light?    (answer)

The color of an object depends on the reflection and the absorbtion of light. How?    (answer)

Do you know of a color/temperature chart showing various colors and their related heat reflection/absorption properties?    (answer)

Why do colors fade in the sun? is it the heat or the light?    (answer)

Do objects that are the same color have the same chemicals (elements) present? For example if I looked at the chemicals in red paint would I find the same ones in a red flower?    (answer)

Is the temperature the same in shadow under a dark colored fabric awning as under a a light colored awning?    (answer)

Sailors know from experience that darker colored fabrics last longer in full-sun exposure than white or very light colored fabrics. I am specifically referring to Sunbrella bimini and sail cover fabrics. Why?    (answer)

How do we see metallic colors like gold and silver?    (answer)

What effect does light have on white paper: does it reflect or transmit?    (answer)

Why does eye (iris) color appear to fade with old age? Is it because of the yellowing of the lens?    (answer)

What wavelength out of red, green, blue and full spectrum would purple cabbage reflect, and what would it absorb?    (answer)

Do clear objects reflect or absorb heat?    (answer)

I am trying to image a white fabric bag using a light source inside of the bag. Are there any wavelengths of light that would be most appropriate? That is, which wavelengths might be absorbed by a white acrylic fabric?    (answer)

What colour paint dries the fastest?    (answer)

In literature about discoloration of wood (furniture or parquet floors), UV-light is mentioned as the cause for the discoloration. But doesn't the glass window act as a UV-filter? So is the discoloration caused by visible light instead of UV-light?    (answer)

Does the color of an ice cube affect the rate at which the ice cube will melt ?    (answer)

Why does some plastic yellow over time?    (answer)

Can one measure color through heat frequencies?    (answer)

What color of construction paper fades the fastest?    (answer)

Can you help me explain (in simple terms for a 5 year old child) why some colors of popsicles melt faster than others?    (answer)

Why does light create color?    (answer)

What colors should I use for my experiment on which colors absorb more heat? I already know I am doing black and white.    (answer)

How do colored objects reflect heat?    (answer)

Does the color of your car determine the temperature in the car?    (answer)

What chemicals are used to create fluorescent paint?    (answer)

Does the color of light affect how much snow is melted?    (answer)

What colors absorb more heat, when a piece of ice is sitting on the piece of paper on a hot and sunny day?    (answer)

Which will melt faster, blue Popsicles or red Popsicles?    (answer)

I want to purchase an LCD HD TV. But I can't decide between 2 TVs. One boasts 3.2 billion colors and the other 16.7 million colors. Do I care?    (answer)

Does the color of water effect its heating rate?    (answer)

I would like to ask if colour filters use to photograph - the filters we use to put in front of a lens in a camera- is a subtractive method?    (answer)

Can white light be captured inside an opaque container. If not, why? When the source is disrupted it becomes dark. why?    (answer)

Of papers colored blue, white, red, green, purple, yellow, and black, which would be easiest to remember things if they all had black letters (except the black paper, which would have white letters)?    (answer)

Why do flat black objects get hotter than lighter colors?    (answer)

Is there a chemical compound for invisible uv red ink compound. How we can get some or make our self?    (answer)

Are there any objects that can physically reflect UV light to be able to be seen with the unaided eye?    (answer)

Does the melting rate of a substance vary by color?    (answer)

How is a star's color different based on the temperature?    (answer)

How can light affect an interior color? For example: what is the effect of natural light on a red wall, blue wall, etc.    (answer)

Does color affect the reflection of heat?    (answer)

I would like to know if there is a way to determine the amount of ultraviolet light absorption by causing a change in the color of a particular substance and what the substance would be.    (answer)

I am trying to get the appearance of gold and silver on my monitor but they always look like yellow and silver. How do you get metallic gold on a monitor?    (answer)

Why does the color blue have higher UV reflectance properties than other colors?    (answer)

Does color affect reflection of heat?    (answer)

To what degree is violet light magnetified to change into UV heat radiation?    (answer)

We design commercial kitchens with lots of stainless steel, white tile, and fluorescent lights. Why do our cooks prefer dark, mat finish tiles?    (answer)

Why are plants green. It seems they should be shades of black.    (answer)

What is the differance in reflective properties between white and orange hard hats working in the sun? I know white reflects more but how much more does it reflect?    (answer)

Does the color of ice affect its melting rate?    (answer)

How does color affect heat absorbtion?    (answer)

Outside my building, someone has spray painted the letters USAF with blue paint. The snow under the paint has melted putting the letters in relief. How come?    (answer)

I have made four boxes out of colored clear plastic and will be putting glass containers inside full of snow inside each one, then leaving them in the sun to see which melts faster. The colors are red, blue, yellow and clear. Can you help me find information on how color will make the snow melt faster?    (answer)

I need a teaching aid that uses three areas of colored cellophane (R,G,Y; or R,G,B) which is set on top of a background with text of different colors. How can I find the right cellophane and text color combinations that will allow the user to see only one group of text, while that same text is not visible through the other two cellophane colors segments?    (answer)

Is there an analytical method for calculating relative powers needed to achieve a specific white balance for monochromatic sources (eg: lasers) of known wavelengths?    (answer)




What percent of light is reflected from Brown beer bottle glass? Green beer bottle glass? Clear beer bottle glass? (921)
The important question is what percentages are absorbed and transmitted. Since the glass is transparent, very little light is reflected and that amount is about the same for each color. It is the percent transmitted that gets through to the beer and gives the glass its color. A clear bottle transmits something like 90% of the light and equally at all wavelengths. A green bottle would transmit a fairly high amount of green light (maybe 40-50%) and very little red and blue light (nearly 0%). The brown bottle will transmit nearly 0% of the blue and green light and then a small amount of red (maybe 5-20%) to get its brown color. Also remember that the transmittance will vary from bottle to bottle. The light that is not transmitted is absorbed by the glass.

If your beer is stored in the dark, then it doesn't matter what color the bottles are. If it is stored in a lighted environment, then the dark bottles (brown) will keep the beer fresher for longer.  (Back to top)


How does a flower´s color help it survive? (896)
The color attracts bees and other insects that pollinate, and therefor propagate, the plant. It also makes the flowers attractive to humans who then care for them and see that they survive to future generations.  (Back to top)


We have a WWI aircraft we are recovering with fabric that requires a dark green paint for the wings. This aircraft is flown a lot and displayed to the public outside quite a bit. The problem is that this paint absorbs sunlight heat dramatically which reduces the life of the doped fabric, causing it to shrink prematurely and it is fairly expensive to replace. Would a primer coat of silver dope or white help reduce the absorption of the heat into the fabric under the dark green paint? (866)
Unfortunately that won't help since the dark green will have already absorbed the light and converted it to heat (a temperature increase). The white or silver layer would only work if it was exposed to the light and then, of course, your plane would be white or silver instead of green.  (Back to top)


I am looking for the differences between red, blue, green, and yellow dye. Can you tell me anything different about them, other than they are different colors? (856)
The dyes will have difference chemical structures that cause them to interact with light differently. For example, a yellow dye absorbs blue light while a blue dye does not absorb that light, but would absorb green and red light. It all comes down to the chemical structure.  (Back to top)


What part of the spectrum helps grass grow? (855)
Chlorophyll in the plants absorbs light and converts that energy into the forms required for the plant to grow. Since chlorophyll is normally green, it is mainly the blue and red wavelengths in the visible spectrum that would be most strongly absorbed to provide this energy. However, a significant amount of ultraviolet energy is also utilized by the plant and even some of the green light is absorbed.  (Back to top)


Why does the color of a crayon or colored pencil look a different color on paper? For example, some purples show up blue on paper. (854)
Because the colorants in the crayon interact with the paper depending on the amount of wax you put down (how hard you press) and the lighting. It is possible to make a wide variety of colors using a single crayon. As more wax is applied to the paper, the color should begin to look more and more like the crayon itself.  (Back to top)


Which light colors are absorbed by a yellow tulip? (844)
Blue.  (Back to top)


What colors (in order) would best absorb a green 529nm laser light? (841)
You haven't provided enough information to answer that question. You would need the spectral reflectance of the material (or transmittance if it was not opaque) for each color and then you would just order them from least reflective to most. For example, a black object would absorb almost all the energy at any wavelength, but a red material might well absorb even more at that particular green wavelength. You can't tell from just the color names.  (Back to top)


Are there established color values for the color of skin for various ethnic groups (like Lab or Munsell for example)? This is for a makeup manufacturer who wants to design packing for specific groups of people. (828)
I am not aware of any specific standards although some might exist. You might look at some of the color imaging test charts (e.g. the Munsell Digital ColorChecker SG from X-Rite that has several skin-tone samples, see this web page to get an array of reasonable colors. (Back to top)


I dyed 100% cotton red, yellow and blue and placed them in direct sunlight for a week. The red appeared to fade the most, but I can't explain why. Can you help? (827)
It's hard to say since it depends on the specific colors and how you measure "fading". The yellow one wouldn't look like it faded much because it is hard to see yellow fading toward white (they are already similar colors) and the red one might have faded more than blue because it is absorbing more blue light, which is made up of the shorter wavelengths, which have more energy and tend to cause more chemical changes such as fading.  (Back to top)


Why does red disappear when viewed behind red glass? (826)
It actually doesn't disappear at all ... it still looks red doesn't it? What happens is that red text (or other patterns) on white backgrounds disappear since the red glass makes the white background appear red as well and no contrast remains. If the red text or pattern was on a black background, it would remain just as visible through the red glass.  (Back to top)


Why can't humans see ultraviolet or infrared energy? (815)
There are a few reasons for the range of wavelengths that we can see. One is that much of the interesting interactions between energy and objects happen in those wavelengths, so there is a lot of information for us to see there. There are also more "practical" reasons. UV energy is often damaging to biological tissue, so it would be potentially dangerous for our visual systems to absorb that energy. Some insect respond to UV energy, but they don't live nearly as long as us, so maybe the potential damage is not so much an issue for them. At the other end of the spectrum it becomes difficult for biological photoreceptors to respond reliably. Basically, because of the temperature of our bodies, receptors that could respond to IR would also be very noisy (IR cameras are often cooled for this reason) and it would be difficult for us to differentiate noise produced by our visual system from objects out there in the world.  (Back to top)


What is the theoretical principals of the color change test in chemistry? (809)
How Stuff Works provides a great explanation and experiment. Here is an example: Printing Industries of America RHEM Light Indicator  (Back to top)


Is color a quality in physics? (798)
The main definition of color is that it is an attribute of the human perception of light. It is not a property of physics (although physics can be used to describe the light stimulus), but a property of human perception. So, according to that definition, the answer is a very definite "no". However the word color is unfortunately sometimes used with other definitions. For example the term "color" is used in physics to describe a property of the theoretical subatomic particles known as quarks. In that sense of the word, "color" would be a quality of physics.  (Back to top)


I have noticed a couple of different species of early-flowering trees have pink blossoms which turn white literally overnight. It is the speed of the process which is intriguing. Do you know how it works? (797)
I don't know the mechanisms for sure, but it could be that the pink colorants are very light sensitive and fade shortly after the flowers bloom. Also, it could be that they are transported quickly to different parts of the flower or spread across the petals as the petals grow (thus diluting the color from pink to more of a white). Plants grow incredibly quickly this time of year.  (Back to top)


How can tulips be so many different colors when they are the same plant? (795)
It is for the same reason that people look different from one another. Part of our appearance (and that of a tulip) is genetically programmed and another part is due to environmental factors. The genetic code of the tulip has the information necessary to produce the chemical colorants in the petals of the flower (or lack thereof) allowing different tulips to express different colors. Humans have spent many years selecting tulips for color and other features to assure that certain tulips have the desired genes. In humans, things like eye color, skin color, etc. are encoded in the genes we inherit from our parents.  (Back to top)


How does chameleon paint (i.e. paint which color depends on viewing angle) work? What is its composition? (782)
Such "effects pigments" work on the basis of interference in the layers of material that are dispersed in the paint. This is the same effect that causes soap or oil films to exhibit a range of colors. The wavelength of constructive interference varies with the angle of illumination and view and that results in the range of colors we see. This website provides a nice overview. You might also search for terms like "interference pigment" or "pearlescent pigment" to learn more.  (Back to top)


Why does your hair change color during the season? (780)
I found this nice answer on the MadSci Network.  (Back to top)


Which minimizes solar heat absorption better, polished aluminium or white paint on it? (778)
It would depend on the specific materials, but in general a good polished aluminum will reflect more light than a typical white paint. The aluminum should be well above 90% reflectance while the paint will be between 80% and 90% reflectance. You also have some control over where the reflected energy goes with the mirrored surface whereas it is reflected diffusely in all directions from a white surface.  (Back to top)


Does the color of a laser affect the velocity of the light wave projected by the laser? (756)
In a vacuum, the answer is "no". The speed of light is the same for all wavelengths (laser colors). In other materials, the speed of light does become a function of wavelength which is why we have dispersion and prisms can separate white light into a spectrum. The change would depend on the material and is defined by the material's index of refraction and how that index varies with wavelength. The index of refraction of air is essentially identical to that of a vacuum for visible wavelengths, so for all practical purposes the answer in air is also "no".  (Back to top)


What is the physics behind a blue-yellow polarizer such as the Singh-Ray Gold-N-Blue filter which photographers use to add yellow or blue highlights to polarized parts of a scene? (755)
I am not very familiar with those particular filters and I couldn't find any details on them. However, it sounds like you are halfway there and what you need is a second polarizer on the other side of the cellophane. When you rotate one of the polarizers, you will get a range of colors coming through the whole sandwich and it will work in either direction. Here is a little experiment from the Exploratorium that does something similar.  (Back to top)


When choosing an umbrella, what color is best to protect yourself from UV light? (748)
Technically it's UV radiation, not UV light, since the term "light" is only used for visible wavelengths. There is not a direct correlation between color and UV absorption/reflection so there is no simple answer to your question. I would suggest you stick with an umbrella that allows no, or very little, light to pass through (e.g., you can't see the sun looking through it) and it will also be very likely to stop the UV energy as well.  (Back to top)


I would like to know if the color of the water (by adding food color dyes) will affect the absorption rate of water and thus the color of the white flower over time. (746)
There is no reason to think that the color of the water will change the rate of uptake by the flower. However, the color imparted will appear different for different colors of dye. Some simply make more visible changes than others. It will also depend on the amount of dye that you put in the water and this is a difficult thing to equalize across different colors. What you are seeing is the different strength of the dyes to produce a visibly noticeable effect. There are many websites with experiments on coloring flowers this way (carnations are a common choice), for example KidZone.com.  (Back to top)


Since a mirror reflects most of the light that falls on it, as does any white body, what is the difference between the two? (742)
This is a matter of geometry. A perfect mirror reflects all of the light that strikes it, but reflects it as regular, or specular, reflection. That means all the light is reflected at an angle equal to the angle of incidence and opposite the normal to the surface. A perfect white also reflects all the light incident on it, but reflects that light diffusely. In other words, the white scatters the incident light in all directions. That's why a white object looks white from all angles, but you can only see yourself in a mirror when you look at it directly (in line with the normal to it's surface).  (Back to top)


I know that the color of a body depends upon the color that it reflects. What causes some bodies to be transparent, others translucent still others to be opaque? (741)
There are many factors involved, but the main one is scattering of light. A material with no scattering can be transparent, one that scatters a little is translucent, and one that scatters a lot is likely to be opaque. And the amount of scattering depends on various material properties such as surface roughness, homogeneity of the material, changes of index of refraction within the material, etc. Also, another important factor is the amount of light absorbed. Something that doesn't scatter at all, but absorbs 100% of the incident light, will also be opaque.  (Back to top)


I am building a pit solar greenhouse and need to decide what color to paint the non-glazed walls. White would be the best for reflection onto the plants but I am also looking for more pleasing colors. What is the best color for growing plants? (734)
Most plants are green, which means they are reflecting more green light than other wavelengths. Those other wavelengths are being absorbed by the plant to help them produce energy. Taking away the green light (which the plants don't use as much) leaves you with purple. So while you are correct that white would result in the most light getting to the plants, as a second choice I would go with a light purple.  (Back to top)


How do mood rings work? (727)
They are liquid crystals that change color with temperature. A nice explanation can be found at owstuffworks.com .  (Back to top)


I understand that the visible spectrum is comprised of the wavelengths red, orange, yellow, green, blue, indigo and violet. Combined they make up white light. So does that mean that white is then a wavelength too? Do all the other colors/wavelengths add up to something that we recognize as white? (708)
There is actually a continuous range of wavelengths between violet and red. The seven names are just a convenient way to divide up the spectrum. White light cannot be described as a single wavelength, but is instead a combination of many wavelengths. Interestingly, you don't need to have energy at all of the wavelengths to make white (for example some displays can make white out of a combination of red, green and blue wavelengths). To answer your last question, yes, all the wevelengths can combine to make something we recognize as white.  (Back to top)


Does the color of your hair affect it's ability to keep your head warm? (707)
If you are in the dark, it won't matter at all. If you are out in sunlight, then darker hair will absorb more of the sunlight and convert it to heat ... making you feel warmer. However, I would guess that the amount of hair would have a larger influence than the color in most circumstances.  (Back to top)


Where do the beautiful colors of fireworks came from? (699)
Various chemicals in the fireworks produce colors due their temperature of burning or atomic/molecular emission. There is a nice article on fireworks here and if you go to the second page there is a link with many more details on light and color in fireworks.  (Back to top)


What makes colors fade in plastics? What part or parts of the light spectum? (695)
A precise answer would depend on detailed properties of the material, but it is probably fairly reasonable to say that any of the wavelengths absorbed by the material will contribute to its fading. Thus, the wavelengths most strongly absorbed are probably doing the most relative damage.  (Back to top)


How do paint colors affect the room temperature? (692)
The paint color probably doesn't have a huge physical effect on room temperature overall. However, when there is plenty of light in the room, darker colors will absorb more light and convert that to heat so there could be some effect. There might actually be larger perceptual effects. Some colors are perceived to be cooler than others (but this will vary from person to person) and therefore people might feel that the temperature is higher in a red room (a warm color) than a blue room (a cool color). I have heard that this perceptual effect can be significant (and applies to lighting color as well).  (Back to top)


Does a sheet of colored glass reflect, refract or absorb light? Or all 3? (680)
Yes, it does all three. It will reflect light at its surface, refract the light that enters the material, and absorb some of that.  (Back to top)


Does the color of glass effect the index of refraction? (670)
Generally, it is assumed that colorants in glass do not affect its index of refraction. However this cannot possibly be true. Depending on the type of colorant and how it is dispersed within, or on top of, the glass, it is almost certain to have some effect. I suspect the effect is often quite small however, but it could be very significant if colorant concentrations were high.  (Back to top)


Why do colors abosorb and/or reflect heat? (669)
That's similar to asking why colors are colors? The chemical structure of atoms and molecules allows them to interact with different wavelengths of electromagnetic energy differently. Some absorb, some transmit, some reflect. There is nothing else that can happen to the energy. I can't say "why", that's just the way nature works.  (Back to top)


What makes wet grass greener than dry grass? A scientific explanation of more than just refractive index would be much appreciated. (631)
Actually, refractive index doesn't explain it very much at all. There is surface reflection at the interface between grass and air that is due to the change in index of refraction (grass different from air). The index of refraction of water is closer to that of grass than air, so it helps the situation. Surface reflection is not colored (not green in the case of grass), but the same color as the illumination. Dry grass has a fairly diffuse surface that scatters that surface reflection in all directions so what you see is a combination of the green (subsurface reflection) plus the white (surface reflection). When the grass is wet, it becomes glossy since the water smoothes the surface. That means all the surface reflection goes off at one angle and becomes a glossy highlight. At other angles all you are left to see is the subsurface (green) reflection and thus the wet grass looks greener (more chromatic) than dry grass.  (Back to top)


I am preparing a 3 band fluorecent lamp powder recipe for color point x=0.312, y=0.336, Ra= 82,SDCM<3. Can you provide any useful recipe development procedures, methods or any useful website for me about the color coordinates adjustment? (628)
This is a very specific application and I would suspect that very little information is in the public domain regarding this topic as it is probably a competitive secret among lamp manufacturers. I am not sure how the fluorescent powders interact, but if you know the color of the individual phosphors (Yxy) then you could predict the color of additive mixutres by simply summing the tristimulus values (XYZ) in absolute units. You could use the same procedure to predict the amounts (or luminance levels) of the three phosphors required to produce your aim chromaticity. This all assumes the phosphors don't interact when they are coated simultaneously.  (Back to top)


I am shopping for a new motorcycle helmet and want to know the color's that would keep my head cooler in the sun. Where do colors such as grey or silver fit in as far as reflecting light/heat and staying cooler? (626)
The coolest (temperature wise) will be white because it reflects all the light. A good shiny silver would probably be close. Black will be the hottest and gray will be in between (probably hotter than silver). For colors, it is hard to say because the color might not necessarily correlate perfectly with heat absorption. However, they will all be hotter than white. Red, for example is nearly as hot as black because it absorbs a lot of energy (all the blue and green light and only reflects the red).

If you really want to keep your head cool ... go with white.  (Back to top)


Can you explain which coloured dyes change colour or fade and why when used as a gamma radiation dose indicator? (619)
Well, I don't know anything about this topic (and I don't think it is familiar to anyone else in the lab), but I found this webpage that seems to explain it pretty well.  (Back to top)


Which colored paper reflects more light? (613)
White.  (Back to top)


The color of an object depends on the reflection and the absorbtion of light. How? (612)
Actually, the color of an object depends on three things, the light source, the object properties (as mentioned in the question), and the human observer. All three are necessary for an object to have "color." As far as the object itself, it is the property of absorbing different amounts of the various wavelengths of light that impart color to the object. Whatever light is not absorbed is either reflected or transmitted and that is what we see.  (Back to top)


Do you know of a color/temperature chart showing various colors and their related heat reflection/absorption properties? (589)
Unfortunately, I am not aware of any such chart and it is unlikely that it is even feasible to make one. Heat absorption properties do depend on color, but they also depend on the material's properties in the ultraviolet and infrared parts of the spectrum and the nature of the illuminating source. So there is no way to consistently match up color and heat absorption properties without knowing other details of the material and illumination.  (Back to top)


Why do colors fade in the sun? is it the heat or the light? (585)
There are a lot of causes of fading, but it is probably more common that it is the light exposure more than heat exposure. Beyond that, exposure to ultraviolet energy is even more damaging in most cases (this is the same stuff that gives us sunburns).  (Back to top)


Do objects that are the same color have the same chemicals (elements) present? For example if I looked at the chemicals in red paint would I find the same ones in a red flower? (577)
Generally no. Simply put, there is more than one way to make the same color. For example, grass is green due to chlorophyll, but my color TV can make that same green color with a combination of red, green, and blue phosphors and a color printer can make grass green with cyan, magenta, and yellow inks or dyes that include no chlorophyll at all. There are lots of different materials capable of producing any given color.  (Back to top)


Is the temperature the same in shadow under a dark colored fabric awning as under a a light colored awning? (573)
As long as you are some distance from the awning and/or their is plenty of ventilation then it wouldn't matter at all. However, a dark awning is going to heat up more (it absorbs light and converts it to heat where the light one reflects most of the light) and then re-radiate some of that heat. Thus, if you are close to the darker awning, or their isn't good ventilation under it, then it will definitely feel warmer under the darker awning.  (Back to top)


Sailors know from experience that darker colored fabrics last longer in full-sun exposure than white or very light colored fabrics. I am specifically referring to Sunbrella bimini and sail cover fabrics. Why? (572)
I am not familiar with the longer lifetime of the fabrics you mention, but it makes perfect sense that the colorants might well protect the fabric itself from harmful radiation (light and UV). The colorants probably end up fading first and then any damage that the light/UV causes the fabric would begin.  (Back to top)


How do we see metallic colors like gold and silver? (564)
We see metallic colors like gold and silver just like we see any other colors. It turns out the difference between metallics and other colors is a physical, not a perceptual, difference. The highlights (where the light sources are reflected) on metals take on the color of the material, while the highlights on other objects take on the color of the light source. That's due to the physical nature of how metals, as opposed to other materials, interact with light. There's a little bit more on this in another FAQ answer.  (Back to top)


What effect does light have on white paper: does it reflect or transmit? (559)
If the paper is a perfect white, then it would reflect 100% of the light incident on it and would reflect that light mostly in a diffuse (scattered in different directions) way. Real paper is not perfect and typically reflects something like 80% to 90% of the light that falls on it. The rest of the light is either absorbed or transmitted. If you can see light through the paper (i.e., it is not completely opaque), then you know it is transmitting some light.  (Back to top)


Why does eye (iris) color appear to fade with old age? Is it because of the yellowing of the lens? (551)
I found a brief explanation online at wonderquest.com. Eye color is determined by the amount and distribution of melanin in the iris (melanin also gives our skin and hair its color). Apparently with age, the density (amount) of melanin can change in the iris resulting in the observed change in eye color. Similarly this can cause our hair to change color as we age. However, the perceived color of our iris does depend to a degree on having a dark area behind it and as we age the lens does yellow. That would make the area behind the iris less dark and therefore change the appearance of the iris. I would suspect that the changes in pigment density are far more important than changes in the lens, however. There are also other causes for changes in eye color that are mentioned in the linked column.  (Back to top)


What wavelength out of red, green, blue and full spectrum would purple cabbage reflect, and what would it absorb? (533)
I'll assume you are asking about the purple parts of the cabbage leaves. A dark purple color like that will absorb a large percentage of most wavelengths. It will reflect some small fraction of the blue, very little to no green, and some red (probably a bit more than the blue). The same could be said for a full spectrum. It will absorb most of the energy in the green region of the spectrum, reflect some in the blue end, and a little bit more in the red end. Of course the best way to quantify this would be to measure a spectral reflectance curve using a spectrophotometer.  (Back to top)


Do clear objects reflect or absorb heat? (526)
Yes. Clear objects reflect and absorb heat. It is impossible to tell from color alone (clear being a lack of color in this case) whether an object is going to reflect or absorb heat or in what proportions since generally no object perfectly reflects or absorbs. For example some types of windows are coated to reflect heat better than others while both will look clear.  (Back to top)


I am trying to image a white fabric bag using a light source inside of the bag. Are there any wavelengths of light that would be most appropriate? That is, which wavelengths might be absorbed by a white acrylic fabric? (520)
The fact that the material is white is an indication that it doesn't absorb any visible wavelengths well.  (Back to top)


What colour paint dries the fastest? (519)
If color is the only variable, then the paints should dry at equal speed if they are in the dark. The lack of light removes any effect of color difference. If they are drying in a lighted environment, then the colors that absorb the most light will dry faster (again all else being held equal). This is because the absorbed light is converted into heat within the paint, which means there is more energy in the water in the wet paint, which causes it to evaporate more quickly. Darker colors will absorb more light and therefore should dry faster.  (Back to top)


In literature about discoloration of wood (furniture or parquet floors), UV-light is mentioned as the cause for the discoloration. But doesn't the glass window act as a UV-filter? So is the discoloration caused by visible light instead of UV-light? (515)
You are correct that glass absorbs most UV energy. For example, we don't get a sun burn through a window. However some UV does get through and this might be enough to cause some discoloration. Also short wavelength visible energy (the violet end of the visible spectrum) definitely gets through the glass and might well be capable of producing similar changes in your wood samples.  (Back to top)


Does the color of an ice cube affect the rate at which the ice cube will melt ? (512)
Assuming the coloring does not change the chemical nature of the ice in any significant way, then ice cubes of various colors will melt at the same rate if they are in the dark. When illuminated, the darker colored cubes (those absorbing more light and converting that energy into heat) will melt faster.  (Back to top)


Why does some plastic yellow over time? (509)
Materials change color over time for a number of reasons. Some chemical reaction is happening to change the structure of some molecule or molecules in the object. These reactions could be facilitated by exposure to light, oxygen, heat, or other things. Without knowing the chemical composition of the material in question and the storage conditions, it really isn't possible to write the specific chemical reaction(s).  (Back to top)


Can one measure color through heat frequencies? (500)
No. There is no correlation between color and reflection or emission in the thermal infrared.  (Back to top)


What color of construction paper fades the fastest? (493)
It is impossible to say without knowing a lot more information. What type and color of paper? What is being exposed to? How are other variables (e.g., temperature, humidity) being controlled? How is "fading" being defined and measured? Etc. The best thing to do is define these variables for the case that is of interest and do an experiment.  (Back to top)


Can you help me explain (in simple terms for a 5 year old child) why some colors of popsicles melt faster than others? (487)
Light colors look light because light from the sun or other light sources mostly reflects (bounces) off them and comes to our eyes. Dark colors look dark because that light doesn't bounce off, but instead gets absorbed by the object. Since the light can't get to our eyes, the object looks dark. That light that doesn't bounce off gets turned into heat and ends up helping raise the temperature of the popsicle faster (therefore making it melt faster). So, darker colored popsicles should melt faster than lighter colored popsicles.  (Back to top)


Why does light create color? (478)
This question can be answered on many levels. At the most fundamental level color is a human perception and that perception arises from the responses of the three types of cone photoreceptors in our eyes. Those photoreceptors respond to light of different wavelengths and therefore it is this light that creates our perceptions of color. Why there are three types of cones and why they respond to the wavelengths of energy they do (light) are questions of the physiology of human cells, the information content in scenes and objects and how they interact with light, and evolution.  (Back to top)


What colors should I use for my experiment on which colors absorb more heat? I already know I am doing black and white. (471)
There is something to be learned from any colors you select. Choose the colors you are interested in learning about.  (Back to top)


How do colored objects reflect heat? (470)
The answer all depends on how you define "heat". If you define heat as infrared radiation (which is only one of many ways that objects can be heated up), then objects reflect or absorb this radiation based on their chemical structure, which defines their ability to absorb, reflect, or transmit various wavelengths of energy. It's difficult to get more specific than that without a particular object and situation in mind.  (Back to top)


Does the color of your car determine the temperature in the car? (467)
The color is one factor, of many, that influences the temperature of the car. In general darker colors will absorb more sunlight and become warmer on sunny days.  (Back to top)


What chemicals are used to create fluorescent paint? (461)
The specific chemicals used by various manufacturers are probably kept somewhat as trade secrets. A wide variety of substances are fluorescent and it is mainly the molecular energy levels that determine the fluorescence. The book "The Physics and Chemistry of Color: The Fifteen Causes of Color" by Nassau is an excellent resource to learn more about the chemical nature of fluorescence. You might also inquire with manufacturers of fluorescent paint to see if you can find out their material properties. For example, you can request technical documentation on products from DayGlo at dayglo.com.  (Back to top)


Does the color of light affect how much snow is melted? (452)
Not much since the snow is white and will reflect all wavelengths of light more or less equally. However if there are colored objects in contact with the snow, then the color of the light will affect how much they heat up and therefore how much they melt the nearby snow.  (Back to top)


What colors absorb more heat, when a piece of ice is sitting on the piece of paper on a hot and sunny day? (449)
Dark ones.  (Back to top)


Which will melt faster, blue Popsicles or red Popsicles? (445)
In the dark, they should melt at the same rate. If illuminated it would depend on the color of the light.  (Back to top)


I want to purchase an LCD HD TV. But I can't decide between 2 TVs. One boasts 3.2 billion colors and the other 16.7 million colors. Do I care? (430)
The human visual system is not capable of distinguishing 3.2 billion, or even 16.7 million colors in a single display. (In fact, there aren't enough pixels on the display to show all the colors at once!). However, that doesn't mean that the capability to display more colors isn't helpful in producing better image quality. For example, if you were watching a DVD with a dark scene that had a lot of subtle gradation you might well see some unnatural contouring on a TV capable of only 16.7 million colors. The more expensive TV with finer color resolution might well produce a significantly better image. It is not so much the total number of colors that matters, it is how they are used. You also might be less likely to see the difference in a store since viewing conditions are not optimal. However that difference might show up when you get the TV home. If it were my decision to make, I would spend the money and get the better color resolution.  (Back to top)


Does the color of water effect its heating rate? (429)
The heating rate of water should only be influenced by color if the water is being heated by the absorption of light (darker colors will absorb more light and convert that into heat). However, if the water is being heated on a stove for example, then the color of the water in the pot should have no influence.  (Back to top)


I would like to ask if colour filters use to photograph - the filters we use to put in front of a lens in a camera- is a subtractive method? (427)
Additive and subtractive methods refer to how colors are mixed, not the properties of a single stimulus (like a filter). Photographic filters work by absorbing light (some wavelengths more than others if they are colored). That is the simple physical process that gives a filter it's color. If you were to stack two or more filters together, then you would use the principles of subtractive color mixing to predict the color of the combination. If instead you were to project spotlights through each of the filters individually and then superimpose the spotlights, you would use the principles of additive color mixing to predict the resulting color.  (Back to top)


Can white light be captured inside an opaque container. If not, why? When the source is disrupted it becomes dark. why? (410)
Theoretically, yes! Unfortunately the container would not only have to be opaque, but a perfect reflector (reflecting 100% of the incident light) on the inside. If the inside was anything less than a perfect reflector, then there would be some probability that light would get absorbed each time it strikes the surface. Since light is traveling so quickly, it wouldn't take long for all the light to get absorbed. Unfortunately there are no such materials to build the container from and, even if there were, you'd have to figure out a way to remove the light source from the container and seal it (so that it was perfectly reflecting on all surfaces) before the light escaped from the opening. That would be quite a challenge indeed. Also, once you opened that theoretical container the light would all escape instantaneously so that the most you might see is a very brief flash.

Real materials quickly absorb all the light when a light source is extinguished or blocked.  (Back to top)


Of papers colored blue, white, red, green, purple, yellow, and black, which would be easiest to remember things if they all had black letters (except the black paper, which would have white letters)? (394)
I am not aware of any research on remember things written on various colors of paper. However, you are probably most likely to remember something that is most legible and the most legible text is that which contrasts most with the background. Thus, white on black, black on white, and black on yellow are likely choices. Black text on red, green, blue, or purple paper would be harder to read because the paper itself is likely to be significantly darker than white or yellow paper.  (Back to top)


Why do flat black objects get hotter than lighter colors? (393)
This is addressed in a number of the answers on our FAQ. A black object is black because it absorbs most of the light that falls on it (light colors absorb very little light). All this absorbed light is converted into heat and therefore the black object heats up more than lighter colors.  (Back to top)


Is there a chemical compound for invisible uv red ink compound. How we can get some or make our self? (388)
I have no idea what an invisible UV red ink would be. If you mean an ink that is invisible, but fluoresces red when illuminated with UV energy, then you need to find a manufacturer of such a material. A web search on "red fluorescent ink" turned up this site riskreactor.com  (Back to top)


Are there any objects that can physically reflect UV light to be able to be seen with the unaided eye? (386)
Since we cannot perceive UV light directly, the only mechanism by which an object can convert UV radiation into visible light is fluorescence or phosphorescence. Thus there are no objects such as you describe.  (Back to top)


Does the melting rate of a substance vary by color? (380)
Yes. If the objects are otherwise identical and exposed to light, then the color will impact the rate at which they heat up (and therefore melt if they get hot enough to melt). In general, darker colors will absorb more light and that light is converted into heat. In the dark, it wouldn't matter what color they are.  (Back to top)


How is a star's color different based on the temperature? (378)
Stars, like other objects emit light based on their temperature. For certain types of objects, called blackbody, or Planckian radiators, you can compute the spectral energy distribution (and therefore the color) of their emission based only on temperature. As these objects heat up, they are first dull red, then orange, then yellow, then white, and eventually blue. There is an equation known as Planck's equation that allows computation of the spectral power distribution as a function of absolute temperature (K). That equation is what let's us know that a blackbody at 10,000K will be bluish and one at 3000K will be yellowish. Since stars are very nearly blackbody radiators, this scale, known as color temperature, allows estimation of the star's surface temperature based on its color.

I hope this helps. This page This page has a little more explanation that might help get you started in exploring this topic more.  (Back to top)


How can light affect an interior color? For example: what is the effect of natural light on a red wall, blue wall, etc. (367)
Unfortunately your question cannot be answered simply. The lighting has a tremendous effect on material colors, but they are not always predictable without detailed knowledge of the material properties and the lighting. For example one blue paint might still look blue upon a change from daylight to incandescent light and another might become purple. There is also a large variation within a given type of lighting (i.e. different phases of daylight, different types of fluorescent lamps, etc.). Simply put, color science can predict the changes that will be seen, but only when the specific material and light sources have been well defined and/or measured.  (Back to top)


Does color affect the reflection of heat? (364)
Does color affect the reflection of heat? Color mainly affects the absorption and reflection of light. Dark colors absorb a lot of light and convert that light into heat. Therefore dark colors tend to heat up more when exposed to light. Lighter colors reflect much of the light and absorb very little, thus there is little absorbed light energy that is converted into heat. A black object outside on a sunny day will warm up more than a white object.

There is more to the story however, infrared energy is sometimes referred to as heat and it could be possible for a black object to reflect a lot of the infrared energy and thus not absorb much of that heat. It would also be possible for a white object to absorb a lot of infrared energy and warm up more than the black object in the presence of another hot object (emitting infrared energy).

So, the general answer is that dark objects reflect less heat than light objects, but it is possible for their to be exceptions.  (Back to top)


I would like to know if there is a way to determine the amount of ultraviolet light absorption by causing a change in the color of a particular substance and what the substance would be. (360)
You might be able to do this by using fluorescent or photochromic colorants. A fluorescent colorant absorbs UV and emits visible energy. The amount of energy emitted would depend on the amount of UV exposure. Photochromic colorants simply change color in the presence of UV and I would expect that the amount of color change could be quantitatively related to the amount of UV exposure. I am not aware of any quantitative systems based on these materials, but this should give you a starting point to search for them or think about making something. Some information about these sorts of colorants can be found in this article.  (Back to top)


I am trying to get the appearance of gold and silver on my monitor but they always look like yellow and silver. How do you get metallic gold on a monitor? (354)
I think you meant to say they always look "yellow and gray." Otherwise you already know the answer!

It turns out that if you look only at diffusely reflected light, gold is yellow and silver is gray. That is exactly what you are seeing on your monitor. The appearance of metals depends on their unique characteristic that their first-surface (or specular) reflection (the highlights on an object) are also colored. This is the appearance difference between a yellow piece of plastic (white highlights ... the color of the light source) and a piece of gold (yellow highlights ... the color of the object). The only way to render these appearances on a display is to add some dimensionality. In other words you can render a 3D object on your monitor that looks like a piece of gold, but you can't make a flat patch of color that looks like gold (unless you render different views of it).  (Back to top)


Why does the color blue have higher UV reflectance properties than other colors? (341)
Blue colors wouldn't have to have higher UV reflectance than other colors and I am sure exceptions can be found. However, in general blue objects are reflecting highly in the short-wavelength end of the spectrum and that reflectance continues into the UV. Another way to look at it is that the wavelengths they tend to absorb are mainly longer than the the blue and UV wavelengths while other colors are largely absorbing the shorter wavelengths.  (Back to top)


Does color affect reflection of heat? (327)
Objects appear different colors because they absorb or reflect different amounts and wavelengths of light. A black object absorbs nearly all the light that hits it while a white object absorbs almost none. A red object absorbs the blue and green wavelengths while not absorbing the red wavelengths. So what happens to that light that gets absorbed? Usually, it is turned into heat and the object warms up. So if you were to put identical objects out in the sun with one painted black and the other white, the black one would absorb a lot of light and heat up much more. So you could say the black object is absorbing more heat from the sun. It's really absorbing more light and converting it into heat.

That's only part of the story, there is a lot of infrared energy out there and that is absorbed or reflected too. The properties of the object in absorbing infrared will influence how much it heats up. However, the properties in the infrared are not directly related to color.  (Back to top)


To what degree is violet light magnetified to change into UV heat radiation? (326)
First of all, magnetified is not a word, so I can only assume you mean "transformed." Electromagnetic radiation is sometimes transformed from shorter to longer wavelengths through processes such as fluorescence or phosphorescence. This type of transformation would convert violet light to something like green or orange light, but not to the shorter-wavelength ultraviolet. It would be very rare indeed, but not completely impossible, for radiation to be converted to shorter wavelengths (which are higher-energy photons). Secondly, heat radiation is normally considered to be infrared radiation (longer wavelengths than visible) and not ultraviolet. It is true that absorption of ultraviolet radiation (or any energy) can raise the temperature of an object, but this temperature change itself is not considered heat radiation (the object might then emit some infrared energy, depending on its new temperature).  (Back to top)


We design commercial kitchens with lots of stainless steel, white tile, and fluorescent lights. Why do our cooks prefer dark, mat finish tiles? (323)
I would imagine that the preference is mainly aesthetics. People do like to have some contrast in their environment and white tiles and stainless steel are both very light colors, thus not contrasting much with one another. The glare from the stainless would be unpleasant and tiring. The darker tiles would reduce this glare by absorbing some of the light that is bouncing around the room. This is particularly true with the mat finish. It is simply because the tiles are absorbing some of the light that might have bounced off the stainless (becoming glare) had you used the white tiles.  (Back to top)


Why are plants green. It seems they should be shades of black. (318)
Here is a website that explains why plants are green. It is interesting, but it really doesn't address your question of why they aren't black. I assume you are thinking that black leaves would absorb even more sunlight and therefore be able to complete even more photosynthesis. I don't know the answer, but I can certainly speculate as a color scientist. There are two reasons that come to mind for me that would make green leaves preferable (and thus evolutionarily advantaged) to black leaves. The first is heat. If leaves were black, they would absorb a lot more light, but they would also have to figure out a way to dissipate the extra heat. Many plants wilt and die if they get too hot, so this would limit the areas plants could live. Green plants reflect/transmit the wavelengths were there is the most visible energy, thus keeping them cooler. That also makes them more visible. The second is translucency. If the leaves absorbed all the light, then there would be none transmitted to the leaves below. Every plant would end up being a single layer of leaves. I would suspect that being an imperfect absorber makes it possible for layers upon layers of leaves to effectively survive. I would also think that these layer's of leaves that are green are making much more oxygen for us all than a single layer of black leaves could. Lastly, you could simply say that green leaves are more attractive to the animals and humans that interact with them and promote their survival. The question to then ponder is why the flowers and fruits are not green!  (Back to top)


What is the differance in reflective properties between white and orange hard hats working in the sun? I know white reflects more but how much more does it reflect? (316)
You are correct that white will reflect more light than orange since the orange helmet is absorbing green and blue light in order to appear orange. However, that doesn't give the full story on perceived brightness (which I assume is your interest for safety). Vivid colors, like a bright orange, look bright not just because they reflect a lot of light, but also because they are colorful. Our perceptions of brightness depends on both the amount of reflected light and colorfulness. The orange helmet is far more colorful than a white one and this colorfulness might be enough to make it look brighter than the white. Also if the orange happens to be fluorescent (like a hunting jacket), then it might look significantly brighter than the white. Ultimately, the best choice is the one that contrasts most with the surroundings. I would expect, in most situations, that bright orange, will stand out more from the surroundings than white. If it was my head, I'd pick an orange helmet. The best thing you can do is to have a few people look at the two choices in a typical environment and choose which they think is brighter (or which is more noticeable). If there is a clear consensus, then you know which to pick. That's a better answer than anything you'll get by simply looking at amounts of light reflected.  (Back to top)


Does the color of ice affect its melting rate? (298)
The short answer is "yes". If there is something causing the ice to be darker, then that means it is absorbing more light. That absorbed light is converted into heat, which raises the temperature of the ice more than similar ice that is not absorbing the light.

There are several related questions this FAQ.  (Back to top)


How does color affect heat absorbtion? (285)
Darker colors absorb more light than lighter colors. Normally this absorbed energy is converted into heat. Therefore, darker colors will normally heat up more than lighter colors. However, there are exceptions. Absorption of energy in the ultraviolet and infrared (some of which actually is heat), also will influence how much an object heats up and it is possible for light colors to absorb a lot of energy in those wavelength regions and vice versa. Therefore the correlation between heat absorption and color is imperfect.  (Back to top)


Outside my building, someone has spray painted the letters USAF with blue paint. The snow under the paint has melted putting the letters in relief. How come? (258)
I am assuming they painted USAF in blue on the snow. When the sun came out, the white snow, since it reflects essentially all wavelengths of light, did not absorb very much energy from the sun and therefore did not heat up and melt. The snow painted blue, however, would absorb most wavelengths of light (absorbing green and red energy is what makes it look blue) and this absorbed light is transformed into heat, raising the temperature of the snow and causing it to melt. Therefore, where the blue letters were, the snow would melt away leaving impressions of the letters.  (Back to top)


I have made four boxes out of colored clear plastic and will be putting glass containers inside full of snow inside each one, then leaving them in the sun to see which melts faster. The colors are red, blue, yellow and clear. Can you help me find information on how color will make the snow melt faster? (253)
The answer to your question depends on the fact that as the plastic absorbs light, that light energy will be converted into heat. That's why a black object (which absorbs almost all light) feels warmer on a sunny day than a white object (which absorbs almost no light). To find the answer to your question, you need to find out which of your containers will absorb the most light. There are two aspects to this. One is the colors (or wavelengths) of light that the container absorbs and the second is the amount of each of those colors present in the sunlight itself. It is reasonable to assume that the sunlight has about equal power for all the colors, so you shouldn't have to worry too much about that part.

So, to figure out which of your containers cause the snow to melt fastest, you will need to figure out which one absorbs the most light. One easy way to do this is to simply look at your containers and put them in order from darkest to lightest in color. That should be the order in which the snow melts as well.

If you want to be a bit more scientific about figuring this out, you need to look at how each container absorbs light of different colors. In a laboratory like ours, we have specialized instruments to measure this, but there is a website where you can get a rough idea. It is this one www.rosco.com, a company that makes filters for spotlights and other uses. If you look at all the filter colors they have (lots of them) and find some that look similar in color to your containers, you can then look at the graphs of how they absorb different colors of light. The filters that absorb the most light will have the smallest values on the graphs and the number at the top of the graphs gives an overall percentage of the light that is not absorbed. The color with the lowest numbers on these graphs should melt your snow the fastest.

There is another complication in your project. How much the glass heats up will also depend on how much of the invisible ultraviolet and infrared energy from the sunlight is absorbed. It is probably safe to assume that all your containers have similar absorption of ultraviolet and infrared, but if you discover any results that can't be explained by the colors alone, it could be due to differences in the absorption of invisible infrared or ultraviolet energy. Unfortunately, you can't figure that out by looking at the containers since your eyes do not detect ultraviolet or infrared energy.

Update! The experiment was completed. The red glass melted first in 1 hour 45 minutes. The blue glass was second and melted in 2 hours. The clear glass melted third in 2 hours and 5 minutes and the yellow one melted 2 minutes later.  (Back to top)


I need a teaching aid that uses three areas of colored cellophane (R,G,Y; or R,G,B) which is set on top of a background with text of different colors. How can I find the right cellophane and text color combinations that will allow the user to see only one group of text, while that same text is not visible through the other two cellophane colors segments? (251)
I'm sure it would be possible, but it will be difficult. To make text disappear when viewed through a given filter, you essentially want to make the text the same color as the filter. For example, red text is visible on white paper because it absorbs green and blue light. If you view the red text through a red filter (also absorbing blue and green light), then ideally you will not be able to see the red text because the stimulus reaching your eye is now the same for the text as it is for the paper. I say "ideally" because it is difficult to perfectly match the text and filter colors. Since you want the text to disappear for two of your filters and be visible for only one, it will be very difficult to find appropriate combinations. It would be much easier to make two parts of the text visible for each filter and one disappear. I won't say it is impossible, but it might be impossible in a practical sense. To get some more information on available filters and their spectral transmittance properties (useful for choosing filters and text colors), I would suggest Rosco as a source of affordable filters. Details on their gels can be found here www.rosco.com.  (Back to top)


Is there an analytical method for calculating relative powers needed to achieve a specific white balance for monochromatic sources (eg: lasers) of known wavelengths? (249)
First, this answer assumes you are using three monochromatic sources, such as lasers. I will use the wavelengths of the three lasers are red = 671 nm, G = 532 and blue = 473. Further, we need to select a target whitepoint, for which I will use D65.
Basically, the solution is to use the CIE color matching functions to find out how much relative power of each of the three wavelengths you need to achieve a desired ratio of X:Y:Z. In your case the desired result is the tristimulus values of CIE Illuminant D65, X = 95.05, Y=100.0, and Z=108.88. The color matching functions define a 3x3 matrix transformation from RGB power levels (on a relative scale) to the XYZ values. What you need to do is invert that matrix in order to compute the required RGB values to produce your given set of CIE tristimulus values. Using your three laser wavelengths the forward equations are:

X = x-bar(671)*R + x-bar(532)*G + x-bar(473)*B
Y = y-bar(671)*R + y-bar(532)*G + y-bar(473)*B
Z = z-bar(671)*R + z-bar(532)*G + z-bar(473)*B

So you have three equations and three unknowns, RGB, since XYZ are defined by your desire to match D65 and x-bar, y-bar, and z-bar are defined as the CIE 1931 color matching functions. FOr convenience, I inverted the matrix and solved this equation in the this Excel file. My results for RGB are 802, 75, and 93 respectively. Normalizing these to be power levels relative to your green laser's power I get ratios of 10.7 to 1.0 to 1.2 for R to G to B. That's a lot of red, but the red wavelength we are using is getting close to the end of the visible spectrum.

Now, here's where a little more understanding of colorimetry is needed. If you set up the lasers to those ratios, you might still need some fine tuning by eye. There are two reasons for this. One is that the CIE color matching functions are an average, their is significant variation from person to person, and you are stressing their accuracy to the extreme in having a stimulus with only 3 wavelengths. The second is that your red laser is at such an extreme wavelength that it is reasonable to expect the color matching functions to have large uncertainty there. I wouldn't be surprised at all if you had to adjust your red laser by a factor of two relative to the above computed ratio. However, the above ratio should get you close to the right answer.  (Back to top)


References

  1. G. Wyszecki and W.S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae 2nd Ed., Wiley, New York, 1982.
  2. R.W.G. Hunt, Measuring Colour 3rd Ed., Fountain Press, England, 1998.
  3. R.M. Boynton, Human Color Vision, Special Limited Edition, Optical Society of America, Washington D.C., 1992.
  4. M.D. Fairchild, Color Appearance Models Addison-Wesley, Reading, Massachusetts, 1998.
  5. R.S. Berns, Billmeyer and Saltzmann's Principles of Color Technology, Wiley, New York, NY, 2000. (from Wiley)
  6. H.G. Völz, Industrial Color Testing 2nd Ed., Wiley-VCH, Weinheim Germany, 2001.
  7. There are several links to GretagMacbeth's Color Conversion Freeware