He didn't come up with it. It's been around for a long time. The formula depends on light spectrum. If done right it is fairly accurate. It's all known math after all.

The problem of exact accuracy is that the advertised spectrum is not exact, so unless you know the exact kelvin of your light, it will be a bit off. But definitely close enough to tell if you're in the right range.

There are websites that can do the calculations for you. But PAR isnt needed. Just use lux or lumens, they are good enough. Unless you're in a lab doing science, there is no reason to be that accurate with your light.

lux meter is good, if you are getting into conversion I think it’s close enough for anyone

I have a par meter..for home science

interesting what he says about apple lux meter, being innacurate...worth investigating what kind of inaccuracy

Boom baby... any thoughts on these numbers?

BabyFarmer said:

Boom baby... any thoughts on these numbers?
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Yup, that's about right. But they arent hard and fast. For me, seedlings and clones seem to be fine up to about 12,000, I veg at 50k and in flower I crank it full at about 75 to 80k on a single 240w quantum board at about 14 to 16 inches.

I've had the numbers up higher in flower, at about 90k is when I noticed my plants actually shying away from the light. But it is probably a combination of genetics, spectrum, temperature, air exchange and co2 levels.

Those are good guide lines. But dont be afraid if they arent bang on.