Light is strange stuff, it is a radiative form of energy transfer, and in order to understand its properties we have to consider it to have both wave and particle properties. Although the sample appears green we cannot quantitate it by monitoring the green wavelength of light. It is this reduction that we can use to quantitate the concentration of chlorophyll. We COULD NOT quantitate it by the amount of green light transmitted (it would be essentially the same amount regardless of the amount of chlorophyll:įigure 5.1.1: Chlorophyll light transmissionĮven though the sample is "greener" with higher concentrations of chlorophyll, this is not due to an increase in the intensity of the green wavelength of light it is due to a reduction in the violet/blue and orange/red wavelengths of light. If we had a sample of leaf juice containing chlorophyll A and B we could quantitate the concentration of chlorophyll by the amount of violet/blue and orange/red light it absorbed. This is the same situation as being in a closed room with the lights turned out.What would an object look like if it contained a pigment that absorbed all wavelengths from 400-750nm? It would be "black".Therefore, plants are "green" because they don't absorb green light. Thus, after sunlight interacts with leaves the wavelengths that remain (and that our eye can perceive) are green-yellow. Light with wavelengths in the range of 500-600nm is not absorbed by either molecule. Thus, these two pigments in leaves absorb violet/blue and orange/red wavelengths of light (the energy that these photons represent is transferred to the chlorophyll molecules). The chlorophyll A molecule has the ability to absorb light with a wavelength in the range of 430 and 660 nm the chlorophyll B molecule absorbs light with a wavelength in the range of 450 and 640 nm. The light from such objects that strikes our eyes (whose color we perceive) is composed of those wavelengths that the object DID NOT absorb.įor example, plant leaves contain two photosynthetic pigments: chlorophyll A and chlorophyll B. Often objects appear colored because of their absorption of light within selective regions of the visible spectrum. Light comprising a specific wavelength within this range is perceived by the brain as being "colored": Samples of light that contain a continuous spectrum of all wavelengths between 400-750nm will be perceived by the brain as "white light" (e.g. The human eye responds to electromagnetic radiation within a range of wavelengths between 400-750 nm (i.e.
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