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Name: Greg V.
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: 5/22/2003

Why do some leaves glow red under black light?


Anthony Brach, Ph.D

You always learn something new!! I did not know that plants were fluorescent. I did a quick Google search on the term "fluorescent leaves" and found a lot of sites. Chlorophyll itself fluoresces and is used to monitor the health of the plant in various contexts; however, it appears that this fluorescence is to weak to be seen visually and is monitored by specialized instruments. But when you think about it many dyes are fluorescent in addition to absorbing visible light, so it is not too surprising that plants would fluoresce.

Fluorescence occurs when a molecule absorbs ultraviolet light which puts the molecule in an excited electronic state. The excited electronic state de-excites be a number of mechanisms. One mechanism is for the electron to fall to some intermediate electronic state emitting a photon. If that photon has a wavelength between 400 and 700 nanometers the eye can detect that light. Sometimes the number of photons emitted are so few that the intensity is too low for the eye to detect. In that case specialized instruments are needed to observe the fluorescence.

Vince Calder

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