effects of colored filtered light on plants

[sharidudes]

My daughter science fair project - The effects of different colored light on green bean plants. She used a different colored light gel above each plant....red, yellow, green, blue, and clear (5 plants total) Each plant has its own box with the colored filter on top and above all of them is a florescent light fixture with two grow lux light blubs. I helped her set up the project so that both the boxes and the light could be adjusted...the light could be kept within a couple of inches above the plants. She knew from her research that the plants under the red and blue filtered light should have done the best..b/c photosynthesis uses these two wavelengths the most. She also predicted that green would do the worst...b/c the plants reflect the color rather than absorb it.

To date, the plants under the red and clear are doing the best, yellow next, then blue, and lastly green. We are quite confused by the growth (or lack growth) of the plant under the blue filtered light. The plant looks healthy however it hardly seems to be growing in height like the others.

Any feedback on what may or may not be happening would be helpful to her. Thank you.

[sunmoonstars]

Hi! That sounds like a great project your daughter is working on. I see you already have the background research done, so you know what results you were expecting. Although the blue didn't do as good as expected, I am curious if it failed altogether? Did the plant die? I suspect you may just be seeing some variability in growth that comes normal in living things.

This is assuming you found everything else was the same in your epxeriement? Such as the distance from the lights, amouont of water, etc.
Could the blue filter be so dark it isn't lettig much light through at all?

I hope another expert has further advice on this one.

Tonya

[deleted-71882]

Hello sharidudes,

One possible explanation for your result is the type of fluorescent bulb you are using. Although the GroLux bulbs are recommended for growing, they do not nearly reproduce sunlight.

Look at this pdf document from Sylvania to see the colors emitted by a Gro-Lux bulb,
http://assets.sylvania.com/assets/docum ... 3e6d08.pdf

Figure 4 shows two spectra for Gro-Lux and Gro-lux Wide Spectrum bulbs. Which do you use?

Notice that the Gro-Lux bulb has relatively little emission at around 475 nm which is blue, so you won't get much light through your filter.

The Gro-Lux Wide Spectrum bulb has a peak at about 440 nm, but if your filter doesn't let that wavelength pass through, then you'll still get little light.

I think you will get a better result if you use "full-spectrum" bulbs rather than "grow" bulbs. But even with so-called full-spectrum bulbs, the light is not uniform at all colors. The light from a halogen bulb is more uniform, but it will be deficient in blue light. Except for very special halogen bulbs, you will find color temperatures of 4000 deg. K or less instead of the color temperature of sunlight which is about 5700 deg K. See http://en.wikipedia.org/wiki/Color_temperature for a discussion of color temperature.

You might be able to get more or less uniform light by using multiple halogen bulbs with the blue filter.

Better yet, could you actually conduct the experiment using natural sunlight?

Good luck, WW