How does color affect heating question

[eagle]

Hi, my experiment is about how does color affect by absorption of light. http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p030.shtml After conducting the experiment, I got some questions about the result.
1. When I first did the experiment, I use incandescent light. However the results were completely out of order. Then I used sunlight instead of incandescent light, I got the correct results. Can you explain why incandescent light make the results completely out of order?
2. The results of my experiment are arranged in the following order: black, blue, green, orange, red, yellow, white. Are the results suppose to be arrange in the order of the wave frequency of the color and why?
3. Can you explain why does yellow have a lower temeprature increase than red or orange if the results are supposed to be arranged in the order of the wave frequency?
Please help as soon as possible. My project is due on 4/16 and I need some time to work on my board. Thanks a lot.

[wendellwiggins]

Hello eagle,

The project description refers to the light source as a "heat lamp" in the Materials list and Experimental Procedure. I think that the intended bulb is just an ordinary incandescent light bulb. I hope that is what you used.

The amount of light absorbed by each color of construction paper depends on its color, but the dependence is not simply "red paper absorbs red light." As mentioned in the Introduction, red construction paper looks red because it reflects red light and absorbs most other colors. Complicating the comparison even more, not all construction paper colors are the same color density. You may actually have two different blue sheets or two different reds.

You give the color order of "black, blue, green, orange, red, yellow, white." Is this the order for sunlight or incandescent light?

In any case, I assume that you give the results ordered from most heating to least heating. This makes sense since the black paper absorbs all colors. Your blue paper is probably a dense, dark blue, so it absorbs all the other colors and maybe even some blue. White and yellow are clearly the lightest colors, so they should absorb the least.

I would guess that sunlight and incandescent light give more or less the same color order, but the lack of green and blue in the incandescent light cause a different magnitude of the temperature differences.

Please get back to me with more information and questions if this note doesn't clear up your results.

Good luck, WW

[eagle]

Thank you so much for helping.
Yes, at first I did use an ordinary incandescent light bulb. However the results I got using the incandescent light bulb were chaotic (you already explained why). That's why I used sunlight instead of the incandescent light bulb. The results I posted: black, blue, green, orange, red, yellow, white were from the sunlight experiment.
If assuming the color density are the same, how can you know some colors are darker than the others. For example, you can't compare red with blue and say which is darker. That's why I'm assuming the amount of temperature increased depends on the wave frequency of the color in the electromagnetic spectrum (except for yellow, which is probably lighter than red or orange). Please explain.
Also, I'm assuming black absorb the most, because black, which is made when all colors are absent, absorb all the colors. White abosrob the least, becasue white, which is made when all colors are presented, reflected all the colors. Is this correct?
Can you also explain why dark colors absorb more light than light colors do? The internet kept on saying "because dark colors absorb more and light colors reflect more." I think there is a better explanation than that.
Thanks again for helping and let me know if you need more information.

[wendellwiggins]

eagle,

I think you understand the experiment and your results pretty well now even though what's going on is a bit complicated. Here are some specific comments on your last post.

You ask, "If assuming the color density are the same, how can you know some colors are darker than the others?" The color density and the degree of darkness are not separate indicators of a color. For example, if a red color were actually a blend of red and white, it would give a pinkish appearance and would reflect not only the red light hitting it, but also some of the other colors. If a red were very pure red, it still might reflect only a narrow range of wavelengths centered on red (650 nm), or it might reflect a wider range of wavelengths centered on the same wavelength. The paper that reflected the wider range of wavelengths would appear brighter (less dark) but both would be relatively pure red. You would need to know the reflectance of each of your papers at all wavelengths to predict just how much light they absorb and convert to heat. Since you don't have this information, let's just assume each paper reflects a pure color band and each has the same wavelength range.

Yes, you are right that black (pure black) absorbs all colors, and white reflects them all. That is why you got black at the most-heated end of the list and white at the least heated end.

Blue comes next in your list because there is relatively little blue even in sunlight and it absorbs everything else. Sunlight has its peak energy in green, so why doesn't green appear closer to white? Yellow and orange are different densities of the same wavelength. Orange can be produced by either light of about 570 nm, or it can be produced by an equal combination of red and green. Yellow is just a brighter (more reflective) orange. It's probably a good guess to say that your yellow and orange papers have a relatively wide reflection band. The heating power of red falls in between orange and yellow because it reflects green light whereas yellow reflects red and green.

The only way I see to explain why green is not cooler than red is to assume that the green paper reflects not all of the green light. The paper maker likely decided that pure green looked too light to match the other papers. Another possibility is that your sunlight was filtered by smog or some other condition that reduced the amount of green relative to red.

You can get a feeling for how much of individual colors make up a particular appearance by experimenting with color mixing on your computer. If you have a word-processing or drawing program, you can use the color tool to see how much red, blue, and green it takes to make a color, or how to set hue, saturation, and luminance to get the result. If you compare colors you get on your screen with the papers you have, you might (might, not will) get a rough idea of the absorption and reflection of each paper. For example, you will see that full-on red and green produce yellow while partial but equal amounts of red and green produce orange.

Hope this helps a bit more, WW

[eagle]

Thanks again for helping.
So based on your information, I have to know which color does the color that I'm testing will reflect in order to know which will abosrb the most light? That's my last question and thanks again for your support.

[wendellwiggins]

eagle,

"I have to know which color does the color that I'm testing will reflect in order to know which will abosrb the most light?"

Yes. Each paper reflects some light and absorbs the rest. The reflected light is what you see when you look at the paper, and the absorbed light is converted to heat. A detailed account of this reflection/absorption would require that you know the reflection/absorption at every wavelength. A much simpler approximate account is just what color the paper appears to reflect (It's red or blue) and how bright it appears.

Don't hesitate to write again, WW.

[eagle]

Oh, I see. Can you tell me the correct results using sunlight of the arranging orders of the colors if all the variables are controlled. I want to compare it to my results. Thanks. Never thought light can be so complicated sometimes.
Edit: Ok thanks.

[wendellwiggins]

eagle,

As we've discussed, some of the ordering of heating vs. color depends on the details of the paper coloring. Here's what I think is likely to be true for most construction papers.

Black heats most because it absorbs all colors. Blue comes next because it absorbs all colors except the relatively small amount of blue in sunlight or incandescent light.

White heats least because it reflects all colors. Yellow is next to white because it reflects both red and green--the most plentiful colors in sunlight.

Red, orange, and green could fall in any order in the middle of the list depending on the details of the light and the paper colors.

WW

[brooke151024]

Hi, I'm working on the same how does color affect heating question, and i wanted to know does it matter to just use sunlight instead of incandescent light? If so would you suggest to using both sunlight and incandescent light, or just either one? Please respomd