Par Meter and LED's

[revhtree Verified Admin]

Sorry if this is dumb but I read something that got me thinking and I need to be clear.

Can I get a correct reading from my LED's with a PAR meter?

 

[Troylee]

Yes and no... Iirc par meters need a special filter to pick up the blue LEDs correctly or I think you just add 10% or something like that to the final tally to compensate for it.... Something like that man haha!:tongue:

 

[reefkoi]

I dont believe a PAR meter has been made that can accurately read leds, I know a white led and blue seem to have identical PAR but ofcourse white looks much brighter to us so it seems the meter cant differentiate between blue and white like it should. Hopefully an expert will chime in here.

C

 

[Mr. Tang]

Do we even know what par numbers we are looking for different corals? I mean like what is a good par for say sps, or lps, or even a softie. How do we interpret the readings?

And better still, how do we know when we have too much light??

 

[Hahnmeister]

Yes Mr. Tang, I could tell you from personal experience what the ideal light zones are for each organism and what an ideal range of values would be for a tank to have. In general, I would say having readings over 700 is for only the most light loving corals and still puts them at risk of frying, although the one exception to all of this is clams... in particular the crocea. You can put those in light levels over 2000 and they love it. Hobbyists like Dana Riddle have also collected readings for the spectra with respect to depth and daily intensity of sun with respect to depth and time; the findings have been published and help us understand what our corals prefer and how we must adapt them to our aquariums.

 

[wld1783]

PAR Meters measure the spectrum associated with photosynthesis. The Royal Blue and Cree Cool White have a very nice 450nm spike which would give you a high PAR reading relative to a brighter light with a more even spectrum.

For softies I like to see a minimum of 100 PAR. For SPS at least 300-400 PAR will good results.

 

[Mr. Tang]

So for my tank (10" shallow tank, with a 50 watt led evolution fixture) I'm limited to what corals I can have because of the intensity of the fixture? Or keep the light so far off the water that it lights the whole room? Or is this fixture not that intense? I have it now 6" off the water and can't seem to keep any sps alive. I have three chalices that seem tone doing ok. Don't they require less light than sps?

 

[reefkoi]

There more to keeping Sps than light so it could be any number of things, on a 10" deep tank with 50 watts you should have plenty of par it's possible too much but just for kicks I'll par test a 50w Evo I have here with it 6" above water and I'll put the sensor about 6" deep and post the number here for reference ok :)
I can't do it tonight but I'll try and get it done tomorrow ok :)
Chris

 

[Mr. Tang]

There more to keeping Sps than light so it could be any number of things, on a 10" deep tank with 50 watts you should have plenty of par it's possible too much but just for kicks I'll par test a 50w Evo I have here with it 6" above water and I'll put the sensor about 6" deep and post the number here for reference ok :)
I can't do it tonight but I'll try and get it done tomorrow ok :)
Chris

Chris
That would be awesome!!

 

[reefkoi]

I've been slacking I had a coral order delayed coming in and so I wasted all yesterday afternoon and half today driving back and forth to the airport and so I haven't had a chance to do anything but I just got in some 1w slims and 3w slims so I want to do some par testing for sure so I'll get to it tomorrow :)
C

 

[Mr. Tang]

Ok thanks

 

[Runner]

More annecdotal than science here, but I have noticed the Cree 3W LEDs have the same PAR readings whether they are blue or white -- and the white have over 3x the lumen output. I figured that was because so much of the PAR sampling was in the blue range where those LEDs are putting all their light. As to the accuracy? I went from 96W T5HO reading of 200 PAR to 48W LED reading of ~500 PAR at my hammer coral. It melted within a month from the light change. Most of my mushrooms let go and fled area of increased light. And I can't say my lumens were all that much higher -- just the PAR reading.

Given how LEDs act (basically Class 2 lasers), they would have a lot of intensity in a narrow band and almost none outside that band. I've wondered if it might be wise to supplement LEDs with a single T5 or CF bulb to small amounts of the other lights, but my tank is doing well and growing with just LEDs, so I can't complain.

 

[wld1783]

Runner

Its more cost effective to choose your LEDs well. T5s are not a bad idea but over the long run they are expensive.

The Cree Cool White have a very nice wide white spectrum. You can make this wider by mixing warmer and cooler Bins. Personally I do like using warm or neutral white simply due to its yellow look. I think your much better off tossing a couple of reds or adding some XP-G for a high noon effect.

 

[Runner]

XR-E royal blues are the ones I meant that had the really narrow spectrum. They peak in the photosynthetic blue range -- which is why I believe they have 1/3 the lumens of XP-Gs but the same PAR readings.

I just use the XP-G white mixed with XR-E blues for the entire day. With this mix I have had good growth with a couple of high-light corals and a clam, so there must be more to LEDs than just skewed readings on a PAR meter. I hate the yellow look and would not use cool white or warm white at all with LEDs just like I wouldn't do so with flourescent tubes or MH bulbs. And I wouldn't use the XR-E whites (8000K spectrum) unless I was going for an economical installation. I would prefer to on alternating banks of XP-Gs or to use a 1-10V signal to vary intensity (with the right controller -- haven't set up my Koyo PLC yet, but getting there) for long term return on efficiency savings.

 

[wld1783]

Runner

You are right on the Royal Blue. In fact below 10 meters there is less white and below 20 there is a lot less with the 450nM being the primary light. Both Chlorophyll A&B are more receptive to the Royal Blue than the White at these depths. I dont think the readings are skewed just realistic based on the photosynthetic properties of Chlorophyll A & B.

There are a lot of ways to do LEDs right and you have done it right. The XP-E R3 at 700mA is very close to the same efficiency of the XP-G R5 at 700mA. The big difference is the XP-G depending in Bin is generally a warmer Cool White than the XP-E. This is why we like to mix them to give a wider white spectrum, also the XP-G can be driven harder 1500mA max.... Lots of different ways of doing it well...

On my personal set up I do alternate banks of XP-G to simulate cloud movement...Really like the look and results.