Help Me Understand My PAR Meter Readings

[mjszos]

Good afternoon,

I have borrowed a PAR meter from my LFS, the Apogee SQ-420, and I'm not quite understanding the output of information, and whether or not the data presented is my "actual" PAR readings.

The Apogee software outputs in umol/m2s - from what I could discern on Google these values are direct PAR readings?

Lighting information:
2x Radion XR-15 Pros (Gen 6)

Tank Information:

48"x24x20

The lights are placed 12" from the side of each tank, on the longest rail that came in the XR-15 RMS tank mount kit. Below are my readings... This seems insanely low for this light? Numbers in the photograph are with the powerheads/pump running to understand what my readings are like in real time. If I place the meter right below the light, at the waters surface it's reading 80.

The numbers in RED are at the front of the rock work. Numbers in GREEN are 6-12" from the front of the scape in either direction. All units are in umols/m2s per the Apogee Connect software.

Am I missing some sort of additional calculation? Is this light really this underpowered @ 100% that I'm only getting 80 PAR 6" below it while the meter is above the water?

Thanks in advance.

 

[mjszos]

I'm realizing this question would be better suited for the Lighting sub-forum. Please feel free to move it if you feel it's appropriate mods :)

 

[oreo54]

I'm realizing this question would be better suited for the Lighting sub-forum. Please feel free to move it if you feel it's appropriate mods :)

Well one thing is the gen 6 have approx 120 degree lenses so the mounting height should be much lower than one expects. Like about 6" off the water line.
As is the height is like 8-9" off the water which is a spread of 28-31"
This is from the central point.. outer diodes spread out of the tank even more.
Second make sure the software is applying the correction for being underwater.
Last the old "original" sensor has a weakness in the blue region:

Still it seems pretty low but these are the obvious errors..

 

[mjszos]

Well one thing is the gen 6 have approx 120 degree lenses so the mounting height should be much lower than one expects. Like about 6" off the water line.
As is the height is like 8-9" off the water which is a spread of 28-31"
This is from the central point.. outer diodes spread out of the tank even more.
Second make sure the software is applying the correction for being underwater.
Last the old "original" sensor has a weakness in the blue region:

Still it seems pretty low but these are the obvious errors..

I appreciate your comments and feedback, regarding the mounting height this is using the official RMS bracket - so it’s at the preset height that Ecotech designed the mount for… unfortunately I have no way of lowering it.

I will be grabbing another PAR meter from a different LFS later this week hopefully as these numbers don’t quite add up. I did have the underwater adjustment checked.

Ultimately even without any deflection from water the PAR meter was reading at 80 umols / m2s at the surface of the water (sensor roughly 8” below the light).

Something tells me this PAR meter just may be on the fritz as in order to get anything above 100 it has to be basically against the surface of the light where it jumps from around 150 -> 1000+