Quote:
Originally Posted by Seamaiden
This is true, and for that we have two other measures that are often not well understood. They are PAR (photosynthetically active radiation) and PUR (photosynthetically usable radiation). Lumens are, for the layperson, along with color temperature ratings, the easiest way to get at what we need, which is to duplicate sunlight.
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It's relatively straightforward for PAR:
Take
this spectrum, normalize the top peak to 1 - so that everything else is a fraction of one - and multiply it times the actual spectrum of the bulb. What you have left over is a weighted spectrum based on plant-useful light.
A simple way to do this is to look at the PAR spectrum and look at the light's spectrum. Peaks at around 450 and 650, with a minimum at 550. You can get an idea of what light is useful with that.