light filters

Fri Jan 24 12:32:17 EST 1997

>The drawback with light color experiments is that students cannot obtain
>the same amount of photosynthetically active radiation (PAR) for each
>color. Incandescent bulbs are rich in red but poor in blue wavelengths
>while cool-white fluorescents are just the opposite. Without an expensive
>PAR meter, a student cannot properly set up a light color experiment to
>compare growth under equal PAR of different colors. Does anyone know a 
>way around this problem?
>The phototropism experiments with different colored windows (red, blue,
>green) in a 35 mm film canister give expected results but probably not
>because the PAR is equal for each color. It would be interesting to
>actually measure the PAR coming through each window under a cool white
>fluorescent bulb.
>David R. Hershey

Light meters are not all that expensive and I cannot imagine trying to
teach or do research in plant biology without one.  A Licor setup runs
about $750 (other companies might offer similar units), they are very easy
to use, and, short of running them over with a truck, should last for
years.  Of course, just having a light meter doesn't make me a light expert
(there are a lot of incorrect ways to measure and express irradiance) but
it is a great instrument to have around the lab.

I have no financial or other interest in Licor.  


Robert R. Wise
Plant Physiologist and Director, UWO Electron Microscope Facility
Department of Biology
University of Wisconsin Oshkosh
Oshkosh, WI  54901
(414) 424-3404 tel
(414) 424-1101 fax
wise at

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