Reading the PAR meter with adjusted results

[OneReef]

I have been reading over the past year or so how PAR meters may underestimate the PAR put out by LED's, especially in the blue range.

Here is a chart posted by someone (Crit21) as a way to adjust the measurements given off by the Apogee PAR meter, such as the one owned by our reef club. I do not propose any of this as fact, but it is interesting and worth further research or reading if this interests you:


Copied and Pasted from here to the end, from a thread on RC:


Measure PAR for each blue wavelength LEDs independently, then multiply the PAR reading by the corresponding multiplier below to get the actual PAR.

Wavelength:
Multiply the Apogee reading by:

400
3.3


410
2.5


420
2


430
1.6


440
1.4


450
1.25


460
1.2


470
1.1


480
1.1

So if you're using 450nm blue LEDs, measure the PAR of the 450s with the Apogee and multiply by 1.25 to get the actual PAR. If you have equal numbers of 450 and 470 blues, you can probably get away with measuring them together and multiplying by 1.2 (the median value for the LEDs between 450 and 470).

This method doesn't work with white LEDs because you can't isolate the blue wavelengths from the total spectrum.