# LED Lights and PAR Readings



## Jarrod987 (Aug 18, 2015)

So for the last 6 months I have been testing the Current U.S.A. LED+ Light. 28-36" model on my 20 gal Walstad planted tank. Photo period is 5 hours on 4 hours off 5 hours on 10 hours off. 
It has approximately 1500 hours of burn in time as of this experiment.
For those of you who do not know. Plants need light of a certain color spectrum. It's more like a range. This range is known as PAR. It means Photosyntheticly Active Radiation. The subject of plant light color and intensity needs is a never ending story I will not get into here. I never read most of that book LOL.
I am one of the few people fortunate enough to be able to own a PAR meter. Mine is a Quantum Flux brand Apogee. The model is MQ-200. I decided to take some readings and share them with the community. The manufacturer has stated there meter is not accurate with LED lights. So my numbers are just for the curios.
This light fixture has 4 channels that control the various LEDs. It has white LED's that are mostly for visual appearance. It also has combination Red,Green, and Blue LED's which are what makes it "Plant Capable". Each color can be controlled separately. When you wish to set the fixture up for plants you use "Full Spectrum" mode which appears to turn all the lights on to the max.
Regarding my tank it is a 20 gal (Long Profile) Tank. It is about 30" long, 12" Front to back, and 12.5" Tall. The LED lights are About 1.5" from the surface of the water and 10" above the surface of the gravel. When you are close to the surface, the amount of light has a lot of variance. This is because the LED's are all point lights. The light has not spread out yet. So right under a LED will be a high reading but just off to the side of it has a much lower reading. The deeper you go, the more the light spreads out. So the variance will be much less. Also, the deeper you go, the water dissipates the light and the readings get lower.

I started with all the LED's fully on:
Just above the surface (In the air) I got
250-300 uM (Micro Moles)
Just below the surface (Under the water just barley)
220-280 uM
Half way to the gravel I got (About 5" deep)
22-105 uM (Plant leaves were causing huge variance)
At the surface of the gravel I got.
30-50 uM

With just the white LED's fully on and RGB LED's fully off I got:
Just above the surface (In the air) I got
180-300 uM 
Just below the surface (Under the water just barley)
180-220 uM
Half way to the gravel I got (About 5" deep)
90-100 uM 
At the surface of the gravel I got.
30-45 uM

With just the RGB LED's fully on and White LED's fully off I got:
Just above the surface (In the air) I got
50-60 uM 
Just below the surface (Under the water just barley)
42-47 uM
Half way to the gravel I got (About 5" deep)
17-20 uM 
At the surface of the gravel I got.
5-7 uM

With just the RED LED's fully on and all other LED's fully off I got:
Just above the surface (In the air) I got
16-17 uM 
Just below the surface (Under the water just barley)
12-13 uM
Half way to the gravel I got (About 5" deep)
4-5 uM 
At the surface of the gravel I got.
3 uM

With just the Green LED's fully on and all other LED's fully off I got:
Just above the surface (In the air) I got
14-17 uM 
Just below the surface (Under the water just barley)
12-13 uM
Half way to the gravel I got (About 5" deep)
4-5 uM 
At the surface of the gravel I got.
3 uM

With just the Blue LED's fully on and all other LED's fully off I got:
Just above the surface (In the air) I got
21-27 uM 
Just below the surface (Under the water just barley)
18-23 uM
Half way to the gravel I got (About 5" deep)
6-8 uM 
At the surface of the gravel I got.
3-5 uM
Enjoy the view.


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## Michael (Jul 20, 2010)

Interesting!

I am now using Finnex Planted Plus and Finnex Stingray fixtures over two of my Walstad tanks. Previous experience with T5 and compact fluorescents taught me to aim for 30-40 PAR at the substrate. The Finnex LED fixtures give me that reading, and the tanks grow as I have come to expect Walstad tanks to grow.

The Finnex fxtures do not allow separate control of different color LEDs, so I can't make the same comparison as you have done. But I am measuring PAR with an Apogee meter, and even though the manufacturer doesn't claim accuracy for LEDs, I think the measurements are close enough.

A further note: I generally do not recommend the Finnex Stingray fixtures for planted tanks. I had to use two of them over a 40 breeder to get enough PAR. They are OK over shallow, narrow tanks, but you will need multiple fixtures over a tank of normal shape. To be fair, Finnex does not market the Stingray for planted tanks--it is definitely their low-end, fish-only fixture.


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## Jarrod987 (Aug 18, 2015)

Yes this one is marketed at plants. I love that the colors can be tweaked separately. I agree with you on the par meter and on the levels. Light of that wavelength range is either present or not. Manufacturer sent me a very scientific article why it doesn't work but I cannot understand it. I also think your 30-40 number is perfect also.


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## mik778866 (Nov 13, 2014)

Hi. It will be interesting to note how these readings will change with the passing of time.


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## Jarrod987 (Aug 18, 2015)

I actually had to turn the lights down a bit so I don't think that data would be accurate now  LED have a much more par then there same amount of visible light from there tube counterparts it seems.


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