Why all the talk about LUX?

[Daniel@R2R Verified Admin]

I've noticed that it seems lately more and more people are talking about lighting in terms of LUX, but it was my understanding that LUX isn't really of much use when talking about photosynthetic creatures and that in a reef tank discussion, we should be talking about PAR (or occasionally PUR). Is there a reason LUX is coming into conversation more often?

 

[steve&mari]

I've understood as you do and wonder myself about it and these free apps people using to place corals?

 

[Daniel@R2R Verified Admin]

I've understood as you do and wonder myself about it and these free apps people using to place corals?

Maybe it's bc of the apps that people are talking about it more, but in my understanding of photosynthesis, knowing LUX isn't really helpful because the amount of USEFUL light (based on PAR) is not the same under every light bulb, so a coral going under X amount of LUX in 1 tank may be getting a total different amount of PAR than a coral under the same LUX rating in another tank.

 

[mcarroll]

More than anything else it's PAR[$xxx] > lux[$xx|$0]

...but it wouldn't be anything at all if it din't work well enough.

For my own case: I would not have toasted a tank full of stony corals switching to LED's back in the day, I had been familiar with the use of a lux meter (or any light meter, really) in this context. As it turns out, I went from >50,000 lux to <15,000 lux. I wouldn't knowingly attempt a change of any more than a few thousand lux.

Good luck sticking to that limit when you have nothing but your eyeballs to go by...which is what almost everyone does.

 

[mcarroll]

(See: I didn't have to mention PAR, conversion factors, chlorophyl, compensation points, lensing, gelbstoff or anything else. )

 

[Daniel@R2R Verified Admin]

More than anything else it's PAR[$xxx] > lux[$xx|$0]

...but it wouldn't be anything at all if it din't work well enough.

For my own case: I would not have toasted a tank full of stony corals switching to LED's back in the day, I had been familiar with the use of a lux meter (or any light meter, really) in this context. As it turns out, I went from >50,000 lux to <15,000 lux. I wouldn't knowingly attempt a change of any more than a few thousand lux.

Good luck sticking to that limit when you have nothing but your eyeballs to go by...which is what almost everyone does.

Ok. So maybe we call LUX the hydrometer of light measurement with PAR being the refractometer? Basically, LUX is better than nothing. Does that sum it up?

 

[mcarroll]

I would draw a parallel with all the test kits we currently use.

None are of "scientific accuracy" but I wouldn't attempt to run a tank without them. (As in, with nothing at all.)

A PAR meter might be paralleled with ICP lab testing. It is better. But, is it required? No.

 

[mcarroll]

Dana Riddle gave me the idea, for what that's worth.

 

[Daniel@R2R Verified Admin]

I dunno. I think LUX falls between "better than nothing" and "good enough." It's definitely a step above eyeballing it, but it's still deficient on many levels. My fear is that people might look at LUX levels and think that's an accurate way to determine a coral's needs when it really doesn't tell us much about what the coral actually needs.

 

[Brew12]

Lux can be measured using an iPhone app or a $15 meter. Par requires a much more expensive meter. If you don't understand the difference between Par and Lux, a Lux meter can give you a false sense of security.
That said, if you do understand the difference between Lux and Par, a Lux meter can be very useful.

This is really a great topic you brought up, I love it!

 

[mcarroll]

I dunno. I think LUX falls between "better than nothing" and "good enough." It's definitely a step above eyeballing it, but it's still deficient on many levels. My fear is that people might look at LUX levels and think that's an accurate way to determine a coral's needs when it really doesn't tell us much about what the coral actually needs.

They really aren't that different in this context.

If they were, you couldn't make a conversion factor for your lux meter to enable yourself to give out accurate PAR readings for your light.

If you look at the available conversion factors – Dana has published maybe a couple dozen, I think. Apogee has published some too. – you can see the "possible range of error" between the two meters, if you want to call it that. (They are both correct, as far as it matters.)

If you narrow that list of conversion factors to lights, or light-combos that put off "roughly 15K to 20K in color" you'll see the range of conversion factors shrink.

I would try using one in the ways you actually need to use it before getting too hung up on the theory behind what's actually happening.

And yes, it's about "better than nothing". You won't hear me talking anyone into selling their PAR meter. I might try real hard to get them to speak in lux sometimes though!

 

[Daniel@R2R Verified Admin]

They really aren't that different in this context.

If they were, you couldn't make a conversion factor for your lux meter to enable yourself to give out accurate PAR readings for your light.

If you look at the available conversion factors – Dana has published maybe a couple dozen, I think. Apogee has published some too. – you can see the "possible range of error" between the two meters, if you want to call it that. (They are both correct, as far as it matters.)

If you narrow that list of conversion factors to lights, or light-combos that put off "roughly 15K to 20K in color" you'll see the range of conversion factors shrink.

I would try using one in the ways you actually need to use it before getting too hung up on the theory behind what's actually happening.

And yes, it's about "better than nothing". You won't hear me talking anyone into selling their PAR meter. I might try real hard to get them to speak in lux sometimes though!

I wasn't aware that you could give out PAR readings based on LUX. That doesn't sound like it would work because of the other variables that are factored into PAR that aren't factored into LUX. Or am I missing something? Maybe there's a bit of research I'm unaware of? How does one speak LUX in a way that communicates PAR?

Btw, this sounds like an article that someone needs to write.

 

[mcarroll]

Maybe there's a bit of research I'm unaware of?

It seems like there's always a huge bit of research I'm unaware of! Getting used to it myself....you might do the same.

The piece that originally got me started:
Product Review: Lighting for Reef Aquaria: Tips on Taking Light Measurements by Dana Riddle

 

[saltyfilmfolks]

I've noticed that it seems lately more and more people are talking about lighting in terms of LUX, but it was my understanding that LUX isn't really of much use when talking about photosynthetic creatures and that in a reef tank discussion, we should be talking about PAR (or occasionally PUR). Is there a reason LUX is coming into conversation more often?

We should understand all three they are so closely related.

The biggest reason for lux is it is acessable to anyone. Any new reefer should have this in their test kit next to their first API. It costs less too. And then you can set your overly powerful mars Aqua with it.
It's actually a must IMO with led.
And it's $14

i do not claim to be smart. Or arrogant. I do not claim to be an expert refer. Ever
I am trained in light.
This is what all the research says.


A lux meter runs on a photovoltaic cell.
A par meter does too
So Does a foot candle meter btw Lux is metric. You can math the conversion.

Photocells are a hundred or so years old
So are light intensity meters

A par meter was not invented for aquariums
It was an improvement on light meters to ascertain a specific data point within light.

A par meter actuall is a highly calibrated light intensity meter.
It measures the color intensity with a photovoltaic cell.
I belive it is still four samples. R G and B and averaged. Or W.

If you look at the apogee website the constant or lux par conversion for direct suny day number is 50.
Dana riddle also uses this number.
Science I have to assume.

Yes. PUR is another discussion entirely as I'm having a heck of a time figuring out if deeper water coral really need that much more blue. Or if it just takes what is available anyway and leaves the rest.
Because I've seen coral grown under Home Depot Phillips led and four year old t12 and anything made by Odyssea :mad:
Makes me wonder why I can't get jbj leds to grow even hair algae much less coral.

I would put forward that.....
During my precious time here using this science I have Been able to estimate MANY members par with specific light fixtures I am familiar with well inside of 100 par.
They own a par meter.
I do not.

100 not sound that great? When was the last time anyone bought a coral that needed to be in 126 par?
It's high low and med. because coral will tolerate wide lighting ranges.

are we chasing par? Yup.

Is understanding it more important than chasing. Yup.

Oh and Dana also says photosynthesis shuts down at 350 par anyway.
So there's that.

My 150w mh 14k gave me 75000 lux at ten inches.
A user recently reported he gets 22000 lux from a kessil 160.
The kessil ap700 at macna gave me 30000 at 12in the perfect perfect even spread on an entire 48in tank.
Yes there will be a test at the end.
It will invilve math.

So if we use the math science gave us with lux, we get a pretty good idea of the range of par in our tank.

Conversion numbers.

T5 coral plus and similar ,14 mh 40 to 45.

Sun , blue plus ,purple plus ,20k mh 50

55 a good LED should be here but I have zero data. Zero.

Meh led 60. probably kessil.
Mars Aqua 1to1 ratio 63.
Consistently from many many sources.

Dana riddle gave 70 for 1to1 led years ago.
Must have been the Jbj

Now go back and do the math.
Then y'all get your par meters out.

 

[mcarroll]

Awesome write-up!

Oh and Dana also says photosynthesis shuts down at 350 par anyway.

Interestingly, I think that's about the same for (most?) land plants as well....photosynthesis can be decoupled from their growth process once irradiance goes beyond this point, is how I've seen it described on that side.

 

[madweazl]

We should understand all three they are so closely related.

...

Conversion numbers.

T5 coral plus and similar ,14 mh 40 to 45.

Sun , blue plus ,purple plus ,20k mh 50

55 a good LED should be here but I have zero data. Zero.

Meh led 60. probably kessil.
Mars Aqua 1to1 ratio 63.
Consistently from many many sources.

Dana riddle gave 70 for 1to1 led years ago.
Must have been the Jbj

Now go back and do the math.
Then y'all get your par meters out.

Kessil 360WE measured 41,800 LUX at 39% intensity (65% color) at the surface in my set up which gives 836, 760, 696, and 643 PAR with conversion factors of 50, 55, 60, and 65. That should be roughly 107,000 LUX at 100% intensity or 1785 PAR (using the "meh" conversion factor) at the surface I'm hesitant to believe but have no way to sanity check it at the moment. I can say 40% was too intense for my duncan that was previously under SBReefs at 35% daylight and 40% blue but also 6" higher in the aquarium.

 

[mcarroll]

Might've been more like 80,000-100,000 lux according to my estimation (40-50 seems a more likely conversion factor range, figuring from the ones available to us), but that's not a great discrepancy.

It's the size of the light change and prevailing nutrient and flow conditions more than the light level itself that causes problems.

I wouldn't knowingly boost light by more than about 2000 lux per incident, myself. I'd allow a week or two between changes, at least.

2¢

 

[madweazl]

Looking at this thread, those numbers might not be so crazy. One thing that doesnt seem to jive is the disparity between the BRS results and the unit being used in the link. BRS had the light mounted at 8" and the user in the link had it mounted at roughly 6.75" (averaged his range). That should only account for a difference in output of about 15% but the results at 6" under water vary by roughly 50%. As usual, lighting by numbers is about as clear as mud.

Edit: BRS ran it at 100% color while the user here was using 65% color (considerably less "white" than BRS).

 

[mcarroll]

Nevermind, eh?

I asked if the OP in that thread would post some numbers at 100%...we'll see.

 

[dragon99]

I found this slideshow interesting. It would be nice to have more info from the presentation.
https://www.google.com/url?sa=t&rct...FVOigoWtnL-FgdH_Q&sig2=4y07h9iqjhENAOVGSCmKVw


Basically, the cheap lux meters we use could be 20% off.