Science Buddies: "Ask an Expert"

Hello. I'm new on this website. My Science Fair Question is "What effect does colored light have on the output of a solar cell". How should I have only one color of light to hit the solar cell? I got a green, yellow, blue, red , and violet color filter. But, I'm not getting the desired results, and I know I'm doing something wrong. According to my research, the blue color filter should have gotten the highest output for the solar cell, but the yellow filter did. I used this website's video, [http://scienceblogs.com/dotphysics/2010 ... ters-work/], to help me. I did the same exact thing he did, from the video, but the red laser was able to pass through all color filters, even blue and green. I believe my color filters are not "correct". If this is so, please give me a "correct" color filter from a website, which only allows one wavelength of light to go through. I must use the five colors I mentioned above as my color filters.

Hi R-Mogulla,

Welcome to Science Buddies! This is an excellent topic for a science project. I think you are doing this project from the Science Buddies website.

https://www.sciencebuddies.org/science- ... #procedure

I’m sure that the laws of physics have not changed, so there must be a reasonable explanation for your results. Perhaps you could do an additional experiment or two to explain your discrepant results. Here are some suggestions that might identify the source of the problem:

In the video, the presenter showed that a specific color of light does not pass through a filter with the same color, but does pass through filters of other colors. The results appear to show that a red filter, for example, adsorbs other colors of light, but allows red light to be transmitted. It sounds like you are seeing light transmitted through all of the filters.

Here are some possible things to check:

1. Are you using laser lights? Check with the manufacturer to make sure that the lights emit only a single wavelength of light. If the light source is white light, then it would produce all different wavelengths of light and would be transmitted through any color of filter.

2. What type of gel filter are you using? In the video, the filters appears to be fairly thick. Try using two or more layers to see if this will change the results. What type of gel colors are you using?

If these suggestions do not help, then please explain again exactly what you have done to obtain your results.

Please note that in science fair projects results are empirical. If you obtain unexpected results, you need to report your actual results and data. However, you do need to explain the results in your discussion and conclusion section.

Please post again and let us know what you find.

Donna Hardy

Hello Donna Hardy,

Thank you for your response. I used this video to help me with my actual test, to see if the other color filters blocked red light. Also, found out that the laser shows a wavelength of 630-680 nm. White light is my control for the test. I kept the color filter on top of my solar cell outside when the sun was there, and I got undesired results.

I bought the color filters on amazon. The colors of the filters are violet, red, blue, green, and yellow.

I took each of the color filters I had, and I cut them into 4 equal pieces. Then I put each of the 4 equal pieces on top of each other, to make them thicker, and I kept the laser on it. The laser finally didn't go through blue and green. It went through yellow, red, and violet though. I did the test outside like this, but I still got undesired results.

Hi R-Mogalla,

It sounds like you are doing the experiment correctly and are getting the expected results.

Yellow is close to red on the color spectrum, and the violet is a combination of red and blue, so these filters are apparently allowing some of the 630-680 wavelengths of light to go through the filter. Is there a difference in intensity of the light shining through the yellow and violet filter compared to the red filter? Blue and green are on the opposite end of the color spectrum and are retaining the red light from the laser.

Results in a science fair project are empirical. In other words, they are what actually happened. If you set up a controlled experiment, you cannot obtain incorrect results. You have obained results that you didn't expect, but that's OK. You just need to explain what happened. You have solved part of the problem by increasing the thickness of the filter, however, the red light is going through the violet and yellow filters, so this is your actual result for your experiment.

Does this help?

Donna Hardy

Hello Donna Hardy,

The intensity is the same of the light shining through the yellow and violet filter compared to the red filter.

The material of the color filter is cellophane. I believe I explained earlier that this was not my actual test, or maybe not. My actual test is to take a solar cell and have it hooked up to a Digital Multimeter, and then to keep it outside when the sun was there, and then to keep the color filters on top of it. I used the laser to see if the color filters would block that color of light since the yellow color filter gave me the best results with the sun shining on it. The color filters didn't block the laser, which led me to believe that this is why the yellow color filter was giving me the best results; other wavelengths of light were also hitting the solar cell.

If I fold the yellow color filter around 4 times in half, the red laser won't go through. But now, the the color filter is too thick for light to go through, only little light goes through.

Hi:

Unfortunately the filters you have allow differing amounts of light to go through them. You would need some method to measure the various wavelengths and intensities coming through the filters. You found that, with the yellow filter, you had to have many layers to block out the red laser filter, and at that point you no longer got much of any light through the filter.

This is a case of not enough control over all of the variables. You can point this out in your write up, but I would also suggest trying to find a way to measure what intensity you are getting through each filter. There are photodetectors that can do this, but they may be expensive. If you can find one to borrow, make sure that you get the data sheet so you can know its sensitivity versus wavelength and compensate for that.

Keith

Hello R-mogulla,

I have a few comments to add to Donna's conversation with you.

Not all inexpensive color filters transmit only a single wavelength of light. All filters transmit some range, but with expensive filters the range can be quite narrow compared to cheaper filters. Some of the filters listed on Amazon provide no information on how much they attenuate off-wavelength colors now about their transmission wavelength range. The set at http://www.amazon.com/Colored-Film-Gels ... or+filters describes the filters as narrow-wavelength filters but still gives no quantitative info. An inexpensive, but documented set of filters is available at http://www.scientificsonline.com/better ... lters.html.

The ouput from your solar cell depends not only on the filter but also on the spectrum of your source. If you place a blue-passing filter above the cell, but the light source has no blue in it, then you still get no output. This might explain your result in which the yellow filter and sunlight gave the best output. A solar spectrum is shown at http://en.wikipedia.org/wiki/File:Solar_Spectrum.png. The solar spectrum at your location also depends on atmospheric conditions. Smog can modify the spectrum significantly.

Good luck, WW

R-mogulla wrote:I did the test outside like this, but I still got undesired results.

If you were attempting measuring the behavior of the photocell outside in daylight combined with a red led light source, the filtered daylight was likely stronger than the filtered red led light source.

All filters or combinations of filters simply attenuate certain wavelengths (or frequencies) of light more than others.
All Solar cells have a response curve that varies with intensity and wavelength.
Additionally, solar cell response curves may also be sensitive to the incident angle of the light source.
If there is any leakage of light that bypasses the filter, your measurements can be affected.

In addition to the transmittance properties, filters also have some reflective properties from each surface. When you stack filters, each of the surfaces has some reflective properties. Only when all surfaces are perfectly parallell and the light source is perfectly perpendicular will the refractive properties cancel out. In all other cases, light will be bent at each surface it interacts with.

Folding gelatin filter material back on itself will ususally cause surface curvature and the refractive and reflective properties may make be affecting your results significantly.

If you have a digital camera that provides RGB histograms, you maybe able to utilize it to help diagnose your results with the various filters and light sources.

Hi,

Thank you all for your help. I have a better understanding of my situation now.

Hello,

I was wondering if anyone can give me a website that sells good color filters, which only transmits one wavelength of light to go through, and not more. This is clearly the issue for my project. The color filters I have are not "good". Price is no problem for me. I need a violet, blue, green, yellow, and red color filter. This project is due next week, so a quick response would be very helpful.

Thanks

Hi r-mogulla,

I think http://www.rosco.com/filters/index.cfm might help. Scroll down to Spec Sheet PDFs and click on "Roscolux color filters." There's quite a range of colors offered, and I think, if you're good with any price, these filters might be fine. Hope this helps!

-RM