PAR measurements. Pumps on/off?

[Dawgvet]

I just rented an Apogee PAR meter. I’m making an assumption that I take measurements with my MP40s running at my normal levels and not shut them off since the refraction from the surface motion affects light penetration? Or do I shut them off to get a “highest” light reading?

 

[JDowns]

I measure both with pumps on and off. Off will give you a better baseline, but with LED's and the pumps on you will then be able to see the spikes in par due to reflection.

 

[Dawgvet]

I measure both with pumps on and off. Off will give you a better baseline, but with LED's and the pumps on you will then be able to see the spikes in par due to reflection.

So, when pumps are on, which number do you use since I’m getting quite a difference in light readings in some spots (over 100). Do you approximate an average?

 

[Eggpaul]

bump

 

[JDowns]

So, when pumps are on, which number do you use since I’m getting quite a difference in light readings in some spots (over 100). Do you approximate an average?

Sorry I missed this.

I use the average between the two as you can get some pretty consistent spikes in one generalized area. I get this pretty consistent in the middle of the tank. There is a thread in the lighting section where @Dana Riddle noted this in one of his tests.

https://www.reef2reef.com/threads/kessil-leds-intensity-and-par.493581/#post-5318043

This may be why some folks cook corals with LED's. If you only measure with the pumps off, you could be getting higher PAR in areas and not realize it due to the shimmer effect.

 

[Dana Riddle]

There is some evidence that the 'shimmer' caused by the lensing effect increases the rate of photosynthesis in some marine alga. I did a test on the effects of shimmer on coral some years ago, and didn't see an increase, but this was before the introduction of strong propeller pumps that can really move water and cause good surface agitation. Maybe I'll revisit this someday (but the thought of building the tanks and jigs makes me groan.)