PAR and LED’s

[bues0022]

I have the club PAR meter right now, well, for about another 12 hours. I’ve been doing the testing and I’m a bit confused. The PAR readings are a lot lower than I anticipated. 

 

I’m running a single radion over a 30 cube tank. I’m using the WWC lighting schedule at 50%, so my overall max intensity is 42%. Previously, I had them as high as 70%. I’ve had to move corals back into shadows and much lower than I thought they would need because they were showing signs of too much light. Growth is going decent right now since I dropped down to 50% from 70%. 

 

The max PAR reading I got, about 2” below the water was 150. According to the PAR meter, my blasto is currently thriving at a PAR of 3. 

 

So, thoughts? Do corals really need less PAR than I thought? I was expecting something in the 2-300 for max, I’ve seen others report values this high. LED’s seem to have troubles with PAR meters, is the reported 10% error actually much more? 

Edited February 10, 2019 by bues0022

[WheresTheReef]

Don't know about a par of 3, but make sure the sensor is pointing straight up. Depending on how much your light diffuses before it hits the sensor LEDs can lead to hotspots. Move it over a little and you can see bumps/dips in readings. Also, make sure and multiply your readings by the correction factor described in the link below. For what it's worth, use the meter as a reference but observing your corals will let you know how they are responding to too much/little light.

https://www.apogeeinstruments.com/underwater-par-measurements/

[Sharkey18]

Interesting. I had the same experience.

 

 I got a par meter for xmas and my reading are a lot lower than I thought also. I was also running the WWC on my rations. I got about 100 on the bottom, 150 in the middle, and a few inches below the top 350. 

 

I am also wondering if I should increase. 

 

 

[madweazl]

How far above the water is your Radion mounted? As mentioned earlier, makes sure you multiply your results by the immersion factor (1.32 I believe). You're the second member that posted really low PAR that I've read about in the past week or so (another reported 0); I'm curious if something has happened to the PAR meter (ambient light in your room is likely well above 3 PAR).

[bues0022]

I have them about 10-12” above the water - mouthed using the radion arms. There are definitely places in my tank where I found 0 PAR. It was in a shadow, but I could see some light in the shadow so I was surprised it was so low. When I pulled it just barely out of the water directly under the lights the values would go up into the 300s, but 1/4” below the water it dropped to half that value. The only way I could get into the 300’s would be to put the power almost all the way up - at values where I’ve killed corals from too much light. 

 

Yes, the sensor was pointing up, and multiplied recorded values by 1.32. The meter did seem to be bouncing around a bit (value of 50 would actually see everything from 40-60, so I recorded 50 as an average). 

 

Oh, and the ambient light in the room(5000k bulb color), at waist height directly below a 65W equivalent LED bulb in my basement with 7 foot ceilings measured 1. 

Edited February 11, 2019 by bues0022

[AlanM]

Ecotech gives pretty good data on what to expect underwater from their lights.  I could believe it would be lower if you had all of your pumps running because the ripple on the top surface combined with the water surface itself can knock it way down.  It should be much higher than 300s if you were holding it in the center of the light outside of the water.  

 

You can set the PAR meter to average more readings so it doesn't bounce around so much.  I'd think it would be in the teens at waist height below a 65W bulb.

[AlanM]

After this and other recent low readings I'm going to send the meter in to Apogee for recalibration.  It only costs $50 and that's what the $5 rental fee goes towards.  Apogee recommends calibration every 2 years anyway.  I'll post on the borrowing thread to this effect too that there will be a delay before the next person gets it.

[maevepotter]

I had this same experience when I had the meter at the beginning of January, I believe. I was getting mostly readings of 30-170, which I don't think was correct based on how my tank looks and the readings my lights are supposed to do. Would it be possible for those of us who got faulty readings recently to borrow it again when it comes back recalibrated?

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