Re: Do different Coloured lights affect plant growth?

Light color does influence plant growth in several ways. However, it is 
difficult for students to compare plant growth under different colored lights 
because expensive equipment is required to assure that each treatment gets the 
same amount of light and just the color is different. If this is not done, then 
plant growth may be affected more by the different amount of light than the 
color. 

Some easier to set up plants and light experiments would be the following:

Examine the effect of light amount on plant growth. You can hang a 4 foot 
fluorescent shop fixture at a 45 degree angle and get different amounts of light 
from one end to the other.

Determine what color light is required for phototropism. This can be done with 
red, green, and blue films and a black 35 mm film can. Punch holes in the middle 
of the side of the film can at 120 degrees apart using a paper punch. Tape a 
different colored film over each hole with transparent tape. Place some wet 
paper towel squares on the film can lid and germinate a small seed, such as 
Wisconsin Fast plant. Place the film can in a light location and see which 
window the seedling bends toward. The control is a film can with no holes.

See if plant growth is better under special plant grow lights (such as Gro-Lux) 
than with regular cool white fluorescent lamps. Use same wattage for each type.

Reference

Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley.