For LEDs, from what I've read, you need to measure PUR readings (Photosynthetically Usable Radiation) not PAR.
I don't know how much PAR the blue LEDs read, but I know someone who only uses blue LEDs on his tank and grows lots of corals. I never would have believed it before. So I'm assuming he's getting sufficient PUR even if his PAR readings are low.
UV emitters, on the other hand, apparently have neither PAR nor PUR. (Any emitter in the 300-400 nm range)
LUX is another reading that doesn't actually let you know how good the emitter will be for growing corals. LUX measures visible light at the 555 nm I believe, which is not necessarily what our corals need the most (they like reds and blues, which LUX does not measure). For those of us who switched from Metal Halide to LEDs, the new lights always seem too dim, especially when dialed down, which is why most reefers make the mistake of ramping up their LEDs too quickly.
Here's a quote from the coral science website:
"For such a species, a light source containing a high amount of blue in its spectrum may provide a lot of PUR. At the same time, this light source may show a low PAR value, if all other colours are emitted in low intensity."
This is the site link:
http://www.coralscience.org/main/art...de-a-coral-lab
Hope that helps.
Anthony