How should we be measuring lights in our tank?

[TbyZ]

There's conversion info for LED's out there too....from Dana, no less.....must be a different article though.

Don't get too hung up on converting to PAR unless you're trying to compare numbers with someone.

Calibrating your lux meter to your light source using a PAR meter (Dana covers this too) is the correct answer if you have to do comparisons frequently for some reason. That way your PAR numbers will be accurate.

I've done lux to PAR conversions quite a bit (I just ÷ 50 for ease), but mostly for fun and for threads online just to promote discussion – not for light setups or anything I do on my tanks though. I just use lux for that. There's no reason for a conversion.

Ok then.

As a experienced lux meter user what lux reading, at the water surface, would you aim for, for a typical sps tank?

 

[mcarroll]

for a typical sps tank?

That whole range should work for most corals, rally and truly!

Painting with a broad brush, most commercial fixtures at maximum will give you around 30,000 lux.....chinese fixtures 50,000+. None are likely to be limiting to you or your efforts.

 

[saltyfilmfolks]

The Photosynthetically Active Radiation (PAR, or intensity) versus Photosynthetically Usable Radiation (PUR, or spectral quality) raises its ugly head...again. This has been debated for about as long as corals have been kept in captivity (for old timers, recall the flame wars on CompuServe's FishNet back in the 90's.) My recommendation:
Measure light some how.
Use a lux meter if you have conversion factors for lux to PAR. If not, it's better than not measuring at all.
Use a PAR meter if you can. Get your club to buy one if it's out of your reach financially (it's a lot more fun to spend your hard earned money on a coral than some boring meter.)
The major issues I have with PUR: 1. It requires a PAR meter at least, but is better measured with a radiometer. Big bucks, and difficult. 2. Green, red, and brown (including zooxanthellate) have different PUR requirements. And you still need to know how intense the light is (back to PAR.) 3. Corals' reflective and fluorescent proteins alter spectral quality of incident light, so it's back to the drawing board.
With this said, I looked at the impact of different lights (20K, 6500K, and so on) on growth rates in non-fluorescent Porites corals. There were differences, but they were found to be non-significant.
Final recommendation: Beg, borrow, or steal a PAR meter. Minimum light intensity (PAR) at the bottom of the should be 100. Maximum doesn't need to be over 400 or so. Corals will still grow at higher intensity, but photoinhibition will likely make it slow.

Hmmmmmm?

Dana's method for converting lux to par is Lux ÷ Constant = µmol·m2·sec

http://www.advancedaquarist.com/2008/2/review

The light source matters in regards to the constant. LED's are not included in Dana's list.

90% of all the leds lights I've researched for lux/par constants has come out to 60 at a 1:1 relationship or all channels at full.

Even when the the ratio changes the numbers generally only changes to 55 or 70. If one does the math at 55, 60, 65 and 70, its a very small difference.

IMO , folks using an extremely high blue ratio without a spectrometer , par or lux meter and a huge understanding of coral biology are just guessing anyway. So using a lux meter with the constant of 6o to 70 (higher blue) is actually pretty darned close for the casual reefer and beginner. Particularly because it's a quantified number to make adjustments with,(6000 lux=100par) and even with a par meter many folks report finding the sweet spot in their tanks is sometimes out side of generally "recommended"par. Particularly in the alk/nutrient consideration with many sps/acropora. (Yes Dana, I'm still glued to that thread ,lol)

 

[saltyfilmfolks]

Ok then.

As a experienced lux meter user what lux reading, at the water surface, would you aim for, for a typical sps tank?

Depth is a consideration first of all and keep thinking in par. Typical old school sps is 200 par on the
bed , but was 700+ at the top if not more.

But were you to say a 24 in deep tank with med high rock work id say start a 25,ooo to 30,000 and then test the bottom of the tank(or not really, you can eyeball it like I do)

 

[HM3105]

I appreciate all the feedback! To be clear, it wasn't Kessil. I'd rather not divulge the vendor nor drag any other vendors into the discussion. I was simply trying to understand if I had been mistaken during the somewhat heated conversation.

I don't remember who mentioned it above but one contributor made the statement that "perhaps they were simply building the best light possible and letting the results speak for themselves". That was basically the argument that was made, I simply don't understand how we can continue down that path when we have the tools to approach this from a scientific perspective rather than just anecdotal evidence.

 

[mcarroll]

Depth is a consideration first of all

Good point! With respect to that, I neglected to state what size tanks I was talking about earlier.....both are similar, at 18" and 19" high. (post amended too)

That was basically the argument that was made, I simply don't understand how we can continue down that path when we have the tools to approach this from a scientific perspective rather than just anecdotal evidence.

If you have a problem with the main tool being used, then I guess this is the point at which you arrive.

Do we know anyone with a radiometer who also has access to a Kessil light????

 

[mcarroll]

(spectro-radiometer?)

 

[SashimiTurtle]

Yea yea I know, Kessil won't release PAR numbers for their lights. Their measured PAR by consumers is a lot lower than other lights...

But here's the thing. You don't need 1000 PAR to grow coral. You're actually inhibiting growth at that range(from everything I've read) and probably cooking corals to death. I've seen some awesome SPS kept under Kessils. I'm growing frags out under a Kessil. I wish the PAR horsepower race would just die. Cheap black boxes have enough PAR to bleach the crap out of SPS corals and they cost a fraction of high end LEDs. Lets work on getting better spectrum and spread out of our LED manufacturers, and drop the PAR arguments...

 

[mcarroll]

Parguments

 

[SashimiTurtle]

Parguments

HAHAHAHAHAHA

 

[HM3105]

Yea yea I know, Kessil won't release PAR numbers for their lights. Their measured PAR by consumers is a lot lower than other lights...

But here's the thing. You don't need 1000 PAR to grow coral. You're actually inhibiting growth at that range(from everything I've read) and probably cooking corals to death. I've seen some awesome SPS kept under Kessils. I'm growing frags out under a Kessil. I wish the PAR horsepower race would just die. Cheap black boxes have enough PAR to bleach the crap out of SPS corals and they cost a fraction of high end LEDs. Lets work on getting better spectrum and spread out of our LED manufacturers, and drop the PAR arguments...

I agree that the race for high numbers is silly. However, the the whole reason I ask for those numbers is to have an idea of how I should use the light or how many I should use, etc. to get where I'd like my numbers to be. Not everyone has access to a PAR meter (lux seems like it might be a reasonable alternative though) but to completely ignore the question and just say "it grows coral, why do you even care?" seems reckless.

 

[Flippers4pups]

I've used the 65:1 formula using a lux meter and using Dana's info from the Macna presentation from last year. I'm having very good growth of my SPS at 250 par at high point on my rock structures. 17" from light to coral, lights at 13" above water line.

It's a guessing game, but it works on my system and my corals are loving it.

 

[Biznizface]

I really need to see what my lights are doing par wise.
Was thinking of getting a seneye for its par meter are they any good ?

 

[saltyfilmfolks]

I really need to see what my lights are doing par wise.
Was thinking of getting a seneye for its par meter are they any good ?

Yes.
The pur function is suspect. The par meter seems about as good as any.

 

[Biznizface]

What's pur ?
So the seneye is good for figuring out my lights output yeah ?
I read it's hard to do it because you have to hold the seneye steady underwater by hand to get accurate readings ?

 

[saltyfilmfolks]

What's pur ?
So the seneye is good for figuring out my lights output yeah ?
I read it's hard to do it because you have to hold the seneye steady underwater by hand to get accurate readings ?

Pur is a bit complicated. Def a google.

But yes, the main complaint is you have to be quite careful while measuring. But it doesn't sound too hard.

 

[imustbenuts]

I purchased apogee's par sensor for $150 and use a multimeter to read the results. I multiply the meter number by 5.4 to get PAR.

 

[mcarroll]

I purchased apogee's par sensor for $150 and use a multimeter to read the results. I multiply the meter number by 5.4 to get PAR.

Have you been able to compare with an Apogee or other calibrated meter to see how close you are?

 

[TbyZ]

I bought a $20 lux meter.

Better than not measuring at all

 

[Salty1962]

I use a Milwakee MW700.