How should we be measuring lights in our tank?

[HM3105]

Hey all,

I had a conversation with a vendor at MACNA regarding the PAR for their lights as I've had a hard time finding actual data for them. During that conversation I was told that PAR is not how one should be measuring light but rather we should be using the spectrum. I thought that was interesting but unusual as I've very rarely seen any other method used. So I wanted to ask all of the experts out there for their opinions.

Thanks for your time !

 

[saltyfilmfolks]

You must have been taking to kessil.

 

[mcarroll]

It's all the same when you get down to you and me. They aren't wrong.....spectrum when watts/nm is accounted for should be close to PAR. PAR is probably a more narrow range of frequencies than what they use too.

YOU should be measuring your lights with a lux meter IMO.

 

[saltyfilmfolks]

It's all the same when you get down to you and me. They aren't wrong.....spectrum when watts/nm is accounted for should be close to PAR. PAR is probably a more narrow range of frequencies than what they use too.

YOU should be measuring your lights with a lux meter IMO.

You should have seen Kessils faces when I pulled out the meter last year.
Very nice folks btw.

 

[HM3105]

Any other thoughts ? @mcarroll why do you like lux over PAR ?

 

[mcarroll]

Any other thoughts ? @mcarroll why do you like lux over PAR ?

Mostly because I can afford the lux meter – nothing against PAR. $12 vs $100 or $500.

If cost were no object, you can do even better than a PAR meter though....but I can't afford that either.

 

[madweazl]

You must have been taking to kessil.

I don't know why they would be cryptic, it isn't bad (I guess it looks bad if you cant generate 500+ PAR these days though ).

 

[Tuffyyyyy]

You must have been taking to kessil.

GOT'EM!

 

[saltyfilmfolks]

I don't know why they would be cryptic, it isn't bad (I guess it looks bad if you cant generate 500+ PAR these days though ).

They refute the use of par as a measurement of light.

Its not me. Do some googling.

 

[TbyZ]

Mostly because I can afford the lux meter – nothing against PAR. $12 vs $100 or $500.

If cost were no object, you can do even better than a PAR meter though....but I can't afford that either.

So what sort of figures are we striving for using a lux meter?

 

[Dana Riddle]

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.

 

[mcarroll]

Use a lux meter if you have conversion factors for lux to PAR. If not, it's better than not measuring at all.

This is my main idea....so many folks still guessing. >99% it seems....and a $10-20 meter is all it takes.

better measured with a radiometer. Big bucks, and difficult.

This is the "better" I was thinking about.

If it was someone else's money (or my money was bigger) I would not limit myself to a lux meter.

No matter what I would not limit myself to guessing without using a meter at all.

(Anti-lux snobbery that you see around in comments occasionally is pointless, even harmful in some cases.)

 

[mcarroll]

So what sort of figures are we striving for using a lux meter?

My low light stony coral tank registers a peak intensity of around 14,000 lux at the surface...it has been as low as 10,000 lux in the past.

My "main tank" registers a peak of around 50,000 lux at the surface. This tank has been as low as 40,000 lux (failing circuit board) up to around 60,000 lux when I ran the fixture at full blast for a while.

Literally anywhere in this range should be fine if you're starting with frags, generally speaking. If you're moving established corals or switching lights, then the goal should be to match the old levels as closely as possible to minimize acclimation stress.

100,000 lux is about maximum for sunlight at the water surface at noon in the tropics, BTW.

No need to approach that number unless you're keeping clams or specifically trying to create a surface/shallow biotope. Light that strong will be stressful to a lot of corals. (No big deals for clams.)

 

[TbyZ]

My low light stony coral tank registers a peak intensity of around 14,000 lux at the surface...it has been as low as 10,000 lux in the past.

My "main tank" registers a peak of around 50,000 lux at the surface. This tank has been as low as 40,000 lux (failing circuit board) up to around 60,000 lux when I ran the fixture at full blast for a while.

Literally anywhere in this range should be fine if you're starting with frags, generally speaking. If you're moving established corals or switching lights, then the goal should be to match the old levels as closely as possible to minimize acclimation stress.

100,000 lux is about maximum for sunlight at the water surface at noon in the tropics, BTW.

No need to approach that number unless you're keeping clams or specifically trying to create a surface/shallow biotope. Light that strong will be stressful to a lot of corals. (No big deals for clams.)

And what waterproof lux meters do you recommend?

 

[madweazl]

And what waterproof lux meters do you recommend?

The kind that fit in a ziplock bag

 

[mcarroll]

They refute the use of par as a measurement of light.

I didn't have time to look hard, but didn't find anything...I would be interested to read anything they've said on the subject.

But wouldn't their (alleged) standpoint make sense if they thought their fixture generated significant amounts of useful light that fell outside the 400-700nm range of PAR?

Whether we agree or not can be beside the point....but I think I understand where they are coming from if this is their thinking.

To put it in my own words, they may be trying not to build or design "to the test" (extreme case: VW diesel, anyone?), but instead to build the best light they can – without regard for the tests – based on the results they get. The implication, I guess, is that their design is results- or experience-based rather than theoretical.

I like the idea. I'd love to be able to test it out in a lab.

 

[mcarroll]

And what waterproof lux meters do you recommend?

The kind that fit in a ziplock bag

I've never taken a measurement underwater. Don't let that stop you – but don't think you "have to" take underwater measurements either.

FYI, corals absorb light from all directions, not just up, so there's lots of room for taking and tracking more measurements than the ones you typically see people quote online.

Interestingly, once you get to a certain depth, there is no more "UP" as defined by where the light comes from. Light gets so diffuse that there is no aim, it just "is".

 

[TbyZ]

My low light stony coral tank registers a peak intensity of around 14,000 lux at the surface...it has been as low as 10,000 lux in the past.

My "main tank" registers a peak of around 50,000 lux at the surface. This tank has been as low as 40,000 lux (failing circuit board) up to around 60,000 lux when I ran the fixture at full blast for a while.

Literally anywhere in this range should be fine if you're starting with frags, generally speaking. If you're moving established corals or switching lights, then the goal should be to match the old levels as closely as possible to minimize acclimation stress.

100,000 lux is about maximum for sunlight at the water surface at noon in the tropics, BTW.

No need to approach that number unless you're keeping clams or specifically trying to create a surface/shallow biotope. Light that strong will be stressful to a lot of corals. (No big deals for clams.)

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.

 

[mcarroll]

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.

 

[Dana Riddle]

Some lux to PAR conversions are briefly presented here:
http://www.advancedaquarist.com/2013/2/equipment