Any depth under led, assuming a basic 14 to 20k spectrum. each light has a different par value. including the Sun. so depth is irrelovant.
http://www.apogeeinstruments.com/conversion-ppf-to-lux/
T5, Led, the sun, different MH bulbs all have a different conversion number. Afet a long time researching I found that 60 is the closest for all led so far.
Mine Is similar to this one. It will let you test higher light levels. https://www.amazon.com/Trendbox-Lux...UTF8&qid=1491844950&sr=8-8&keywords=lux+meter
Milwaukee makes one that can be used under water.
https://www.amazon.com/Milwaukee-In...491845031&sr=8-1&keywords=milwaukee+lux+meter
I only test the top of the tank and estimate the bottom. If you can test the bottom, you'll want about 100 PAR or more generally.
First of all thanks for the explanation.
This theme of the lights is really complete, or so I think.
Now that you mention the Kelvin, what should be the proper Kelvin measure? Or does not this have to do with the PAR that has?