ISO: Help with PAR readings

[chaostactics]

I think I'm doing it wrong?

Using an Apogee MQ510 in perfect condition as far as I know.

 

Also is there a template or program out there to grid your tank in 3D to record readings on?

 

I'm testing my lights Radion XR30pro G4 WITH Radion diffusers on RMS mounts (about 7" above tank+ 2.5" rim to waterline) and about a 10-15 degree tilt toward the back of the tank due to the weight of the XR30 or "design" of the RMS

 

I've attached a diagram of the lighting and tank. Sand bed is black and about 2" deep. 

Tank is 24" x 32" x 24" LxWxD. Lights are about 3" from each left and right edges and about 4.5" back from front edge. 

 

Also attached is the lighting scheme. I was running the preloaded radiant color scheme at 59%.

Anyway took some measurements figured I was doing it wrong and gave up. Dead center in my tank left to right, top to bottom, front to back I got ~315 PAR (took the measurements at 57% not full 59%) and all the way down on the sand bed approx 1" from the glass and approx 7" I was getting ~330 PAR.

 

Also of note I'm just remembering I had forgotten to shut off my pumps. So I'm guessing the par may be higher and I can't recall if I scraped the glass first.

 

I realize 2 x XR30PRO are big for this tank but I was truely caught off guard by the readings. 

 

Is it possible I'm getting it right before I go though and do a ton of readings? (With the pump off) And adjust my lights to desired PAR 70-150 or so. 

 

TIA

[mcarroll]

1 hour ago, chaostactics said:

Also of note I'm just remembering I had forgotten to shut off my pumps. So I'm guessing the par may be higher

Consider whether you're testing your lights' performance or whether you're testing the conditions the corals will be living in.  I suspect you only care about the second one.  

 

So unscraped algae and pumps running will be the norm.  So those are the correct testing conditions.  

 

You should actually see the number on the Apogee change quite a bit during any given sample and you'll have to "eyeball" the variable reading to select the highest number.  (A natural reef can be one of the most dynamic lighting environments with daylight levels reaching up towards 10,000 PAR thanks to "lensing" and "flicker effects".)

 

1 hour ago, chaostactics said:

Is it possible I'm getting it right before I go though and do a ton of readings?

As for whether you were sampling correctly, I'll assume you have already (or soon will) watch some YouTubes.  It's not rocket science, but like anything it can be done wrong.  

 

But if you want to do a sanity check on your PAR meter or your sampling technique, then test a light source of a known output level (e.g. bright sunlight on a clear day) and see if the Apogee gives you a reasonable measurement.

 

Do you have a lux meter you can compare readings with (even a smartphone lux meter app)?  A comparison with sunlight is easy since the PAR-to-lux conversion factor is x50.  (100 PAR  = 5,000 lux; 2000 PAR=100,000 lux)