Why blue light affects vegetation growth.
 

Plants can use blue light in photosynthesis. Search for a
photosynthesis action spectrum as in Figure 7 of the first reference.
Chlorophyll has an absorption peak in the blue. Do a google.com search
for a chlorophyll absorption spectrum (see reference 2). Keep in mind
that the chlorophyll absorption spectrum is misleading because it
represents the behavior of chlorophyll extracted from the leaf and
dissolved in an organic solvent. Intact leaves use green and yellow
light fairly efficiently in photosynthesis contrary to what the
chlorophyll absorption spectrum suggests.

Blue is also the light color that activates phototropism,
photomorphogenesis and some other responses (see references 3 and 4).

Blue wavelengths are found in sunlight (reference 5) and in many
electric light sources. Figures 1 and 2 of reference 1 indicate the
wavelength distribution of one electric light source. For wavelength
distributions for other electric light sources, do a google.com image
search for the spectrum, e.g. incandescent spectrum or cool white
spectrum.

Figure 7 of reference 1 indicates that contrary to popular
misconceptions:
1. Leaves reflect a small percentage of the green wavelengths.
2. Leaves absorb more than half of the green wavelengths.
3. Green wavelengths are used fairly efficiently in photosynthesis.

David R. Hershey



References

1. Balegh, S. E. and Biddulph, O. 1970. The photosynthetic action
spectrum of the bean plant. Plant Physiology 46: 1-5.
http://www.plantphysiol.org/cgi/reprint/46/1/1

2. Google.com search for: chlorophyll absorption spectrum
http://images.google.com/images?hl=e...ch&sa=N&tab=wi

3. Phototropism - Do Fast Plants Prefer the Blues?
http://fastplants.org/pdf/activities...efer_blues.pdf

4. Photomorphogenesis: Blue light response
http://faculty.washington.edu/ktorii...371_020515.pdf

5. Google.com search for sunlight spectrum
http://images.google.com/images?svnu...&btnG =Search

6. Hershey, D.R. 2004. Avoid Misconceptions When Teaching about
Plants. ActionBioscience.org original article.
http://www.actionbioscience.org/education/hershey.html