Quote:
Originally Posted by The Peloric Orchid
I strongly recommend buying a lux or footcandle meter. I got one for around twenty bucks on Amazon ... The main downside with these kinds of meters is that they're calibrated to more sensitive in the green/yellow range, much like human eyes, so they won't measure colored light accurately. The alternative is to buy a PAR quantum light meter, but these are much more costly and there's less data about orchid growth in light levels measured in micro einsteins.
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The PAR light meters just do not have the green filter that other light meters have. The frequency response of a photocell without a filter is fairly flat so a green filter is added to make the response more closely match that of the human eye.
The inexpensive light meter that I bought on Amazon had a green filter that I easily removed. Of course, that messes up whatever absolute calibration the meter may have had but if you only care about comparing relative values for varied light sources - sunlight, fluorescent, red LED etc. it now matches the PAR meter response.
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