Measuring PAR of LEDs

[WheresTheReef]

I just borrowed the WAMAS Apogee Quantum PAR meter today. I plan to take measurements at different points in my tank with different light channel intensities of my Evergrow it2080 LED light. I have read that the meter doesn't read the PAR of LEDs correctly and need to be corrected for more accurate results. I came across this page (http://www.apogeeinstruments.com/light-intensity-measurements-for-light-emitting-diodes-leds/) that describes the error. If I read this correctly, would the meter value read ~15% lower than the actual PAR based on my layout given below? I figured that correcting for mostly the 12k and 450nm light would be sufficient since they represent around 75% of the light output.

 

LED - #LEDs

-------------------

12k White - 28

6500K White - 4

420 Purple - 6

450 Royal Blue - 46

480 Blue - 4

520 Green - 4

660 Red - 4

480 Moonlights - 3

 

Anyone with the similar light correct for the values given by the PAR meter?

 

thanks,

Eric

Edited August 23, 2014 by WheresTheReef

[Origami]

I think that it's going to be tough for you to get a corrected-reading using the data from that paper. While it tells you something about the measurement error for each color LED, the light output for your setup will depend partly on the current driven into each color. This will affect the error contribution for only part of the total error and, therefore, the impact on the overall reading that you get. For example, if you ran the blue LEDs with less current, the light output would fall as would the error from that component. However, the percentage effect of the error is different for the overall error measurement. That is, if the error for the blue LEDs was halved, the effect on the overall error is not going to be 1/2 (uless the array consisted solely of blue LEDs). If you could measure each color separately, you could make the corrections and, by adding up all of the PAR measurements, get a reasonably well corrected number.

[zygote2k]

Can I ask why are you measuring PAR of LED's?

[WheresTheReef]

The LEDs are broken up into 2 channels. I was thinking about running both channels at the same intensity to keep things simple. At the end I just want an estimate of the PAR at different locations within the tank. I am just simply trying to get a closer estimate to the "real" value.

 

Another issue is that the meter might be in "electric" mode instead of "sun." The model is an apogee quantum QMSS, but the s/n starts with ELEC. From http://www.apogeeinstruments.com/content/QMSS.pdf and http://www.advancedaquarist.com/2013/2/equipment, the sun mode is more accurate for our application and the electric mode will read 10-15% lower.

 

Seems like there are errors from using LEDs, as well as reading in the "electric" mode (if in fact electric).

 

 

Can I ask why are you measuring PAR of LED's?

 

I want to get an understanding of the lighting at different points in my tank. I am also still ramping up my lights and want to know my target intensity/channel. I want to make sure the corals are getting enough light within their recommended ranges that is why an estimated PAR reading is enough for me. The only thing is that if the error is around 15-25% (e.g. LED error + electric mode error), that can be pretty significant at the higher values (e.g. reading of 400)