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A PAR Meter


  1. Apogee PAR/PPF Meters
    by exquzmwa/ (Exquzmwa) (10 Feb 1998)

Apogee PAR/PPF Meters

by exquzmwa/ (Exquzmwa)
Date: 10 Feb 1998

<Also posted to rec.aquaria.freshwater.plants, rec.aquaria.freshwater.misc>


I was wondering if anyone out there has used the Apogee PAR meters and could
provide an opinion on how well it (actually) works as compared to a standard
lux meter.  Based on documentation chart, it looks like the spectral response
can be pretty far off for some of the wavelengths used by plants.  In
particular, at 400 nm the detection looks to be 70% low, at 450 nm 30% low, at
500 nm it's about right, and then above 550 it's higher than it should be
(couldn't guess the percent over based on the chart).  It basically has no
sensitivity from 650 nm and above.

My main question is:  Is this meter really a better guesstimate than the
guesstimate one would be making using a standard lux meter?  The information on
the web site for the Apogee meter says the low readings on blue and high
readings in the yellow/orange area average out to make things accurate since
bulbs tend to have a spread in the spectrum they produce.  They also quote a
specific error factor based on type of light (MH, HPS, Sun, Incadescent). 
However, I don't see how this can be accurate information since there are
multiple bulb types in each of these categories which produce a variation in
the spectral areas they emit.  I'd guess without looking at the light spectrums
for the various metal halide bulbs that this "averaging low blue values and
high red values gives an accurate result within 3%" can't be true for all of
the metal halide bulb types available.

I know that standard lux meters can be way off depending on the light spectrum
being emitted by a bulb, but I must be missing something as I don't understand
how the Apogee Quantum meter can be much more accurate itself.  Surely I'm
missing something obvious, otherwise they wouldn't make the accuracy claims
they make for the quantum meter....



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