light filters

Barry Meatyard Barry.Meatyard at CSV.WARWICK.AC.UK
Fri Jan 24 05:36:29 EST 1997


>To: plant-ed at net.bio.net
>From: dh321 at pgstumail.pg.cc.md.us ("David R. Hershey")
>Subject: Re: light filters
>Date: 23 Jan 1997 16:40:56 -0800
>Sender: daemon at net.bio.net
>NNTP-Posting-Host: net.bio.net
>Status:
>

On 23rd Jan David Hershey wrote:
>
>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.
>


Yes, the measurement of PAR IS a problem! I don't pretend that the film can
investigations are the definitive solution, but they are a good starting
point for discussion of the principles involved.  There is a good
discussion of the problems of measurement of light intensity at different
wavelengths in Light and Plant Growth by J.W.Hart Unwin and Hyman 1988.

I've even tried asking the physicists here - they don't seem to have a
solution either!

Barry

Dr.Barry Meatyard                       Tel: 01203 524228
Science and Plants for Schools          Fax: 01203 523237
Institute of Education                  Email: barry.meatyard at warwick.ac.uk
University of Warwick
Coventry
CV4 7AL
UK

Dr.Barry Meatyard                       Tel: 01203 524228
Science and Plants for Schools          Fax: 01203 523237
Institute of Education                  Email: barry.meatyard at warwick.ac.uk
University of Warwick
Coventry
CV4 7AL
UK





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