Re: I am doing an experiment growing marigolds under colored light.

Complete question:

I planted 4 plants under clear, red, yellow and green cellophane.  I found 
information that said red light has the longest wavelength.  It also said 
that waves with shorter wavelengths carry more energy.  I can't find any 
information that will explain why the red plants, with the longest 
wavelength is about 3 cm taller and healthier looking than the others.  
Clear is the smallest.  Where can I find information that I can understand 
as to why this is happening.  I've looked everywhere.  Thank you!

Reply:

One possibility is that your red cellophane plants got more total light for 
photosynthesis than the other colors provided. Another possibility is that the 
red cellophane let through more far red wavelengths, which promote stem 
elongation. Were the red plants just taller or were they substantially bigger, 
as in number of leaves, leaf size, or weight?  

It is very surprising that the clear plants did the worst. What was your light 
source, a windowsill or an electric light? Could the clear light plants have 
gotten sick or damaged or have had less light than the others?

The fact that red wavelengths have less energy than blue or other colors is not 
really an important factor in your experiment.