Make sure on PAR you don't compare LEDs to T5/MH. LEDs have very tight wavelengths for the most part so if you get one to shine blue that's all you get no mix of bit green in there or something.

What that means is that with LEDs we can choose to have only wavelengths that are useful for photosynthesis without any extra ones that are just there wasting power. This is where part of power saving from LEDs come from, other than they are a bit more efficient than say MH. In efficiency MH is probably should be called a heater and then a light source

Anyways, these select wavelength do mess with PAR readings on meters as none that we have so far are built or calibrated for LEDs. As such it's a pretty safe bet to add about 10-15% to the readings you might get from a par meter.

Lumens is not very meaningful measure and there is no formula to go from it to PAR, although you could get some sort of guesstimate.


As far as actual PAR values, from what I read for SPS going over 400 in most cases is useless or even detrimental. Basically, corals can absorb only so much before they are "full". Having around 150-200 PAR on sand bed and 350-400 on top of the rocks would probably be a good point for a mixed coral tank with decent amount of acros milies etc, while having spots where LPS can live happily as well.