MadSci Network: Botany

Re: How much light does chlorophyl absorb? How much other materials?

Date: Fri Dec 6 20:27:03 2002
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1039133495.Bt

You have several questions here. Chlorophyll absorbs most light colors poorly. 
A chlorophyll absorption spectrum shows it absorbs mainly in red and blue but 
poorly in far-red, orange, green and yellow. If you measure the area under the 
curves in the Chlorphyll Absorption Graph, you can calculate the 
percentage of total light absorbed. 

White light is a mixture of colors. ROY G BIV is a memory aid for colors, from 
high to low wavelengths: Red, Orange, Yellow, Green, Blue, Indigo, Violet. 
Therefore, white objects, like a white T-shirt, reflect all colors. Black 
objects absorb all colors. 

An object that absorbs all colors is black, not invisible. To be invisible, you 
would have to transmit all colors, like a pane of windowglass or the gases in 
the atmosphere.

It is a common misconception that leaves do not reflect all green light. They 
usually absorb more than half the green light, reflect maybe 10% and transmit 
the rest, unless it is a very thick leaf, like a rubber tree (Ficus elastica), 
and transmits virtually no light. In a dense forest, it can be very dark, 
indicating that multiple layers of leaves absorb all light, even green light, 
efficiently. Other pigments in leaves, such as carotenoids, absorb colors that 
chlorophyll does not.

The amount of light absorbed by a leaf and used in photosynthesis is shown by a 
Action Spectrum.

More Discussion

Re: Why photosynthesis pigment of plant is green and not black?

Re: what is meant by an action spectrum as opposed to an absobrtion spectrum

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