MadSci Network: General Biology

Re: How is plant growth affected if placed in different types of light

Date: Sat Dec 4 23:22:50 1999
Posted By: Richard Kingsley, Science teacher
Area of science: General Biology
ID: 941151072.Gb

Hi Susan,

This would make a great science project.

Light is made up of different wavelengths, which we see as different colours. Organisms absorb light using pigments. Leaves are green because the chlorophyll pigment reflects green light. Therefore under just green light the rate of photosynthesis declines because less of this wavelength range is being absorbed.

The graph below shows how the rate of photosynthesis varies with wavelength. I have also put a colour spectrum above which approximately represents the wavelength on the graph.

You can see from this graph that the rate of photosynthesis is high in the violet, blue and red parts of the spectrum. It is low in the green part of the spectrum. Chorophyll is not the only pigment involved in photosynthesis. Carotenoids and phycobilins are also involved. The graph below reflects all of the pigments together in their ability to absorb light.

Therefore, under green light you could not expect plant growth. You might be wondering what sort of light bulb works best. From the graph, you can see that lights with more blue in them will work better than standard bulbs. You can find lights, which are specifically designed to help plants grow, that have this bias in their spectra.

Richard Kingsley

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