Target Lighting LUX

[Canoe]

I know. LUX isn't PAR, let alone PUR.
But I can get lumens, candle power or LUX, and then with the heights and angle I can calculate whichever of those is missing, thereby being able to calculate the LUX at whatever distance from the light source. Then with the spectrum, I can choose one which will give me good PAR/PUR for my LUX lighting dollars.

I've found info on the net, but I'd like to check it. It's for those of us without a PAR or PUR meter, nor the ability to calculate what PAR or PUR to expect from the hardware.

The words of wisdom I've found suggest
From the wild:

• most of our corals come from 15' to 65' down
• SPS corals can come from within a meter of the surface, hence need much more light
• surface sees 77,000 to 140,000 LUX
• 1m sees 20,000 to 25,000 LUX
• 5m (~16') sees 20,000 LUX
• 20m (~65') sees 6,200 LUX

Tanks:

• tank should have a minimum of 3,000 LUX at the bottom
• SPS tanks should have 25,000 to 40,000 LUX at the surface

Given the above, to get the SPS target of 40,000 LUX and the 65' level of 6,000 LUX, would a good starting target LUX for a marine tank be 40,000 LUX at the surface and 6,000 LUX at the bottom? Of course with is a "dry" calculation, as in, without being able to account for absorption and dispersion of the water, so the actual values in the water will be reduced some.

At what point does bright light for corals no longer work for having fish?

Does anyone put reflectors on the outside ends of their tank to improve restrike lighting within the tank, or does the glass sides take care of that?
(I assume mirrors would drive the fish nuts)

[Hookup]

Unfortunately there are no reliable ways to use LUX in place of PAR that I am aware of, nor do I think there can be.

I'm sure you've found out so I'm adding these short-descriptions and links for any others reading;

LUX is a measure of "brightness as referenced by the human eye".  Its got math/calculations that bias the result to more heavily weight 550nm around a bell-curve.

PAR is photosynthetic light hitting a surface.  This is raw energy (photons) that hit a surface between 400-700nm.  A great measure of how much photosynthetic energy is hitting our corals, but not a measure of photosynthetic efficient per watt of power. (then you need PUR)

But I can get lumens, candle power or LUX, and then with the heights and angle I can calculate whichever of those is missing, thereby being able to calculate the LUX at whatever distance from the light source. Then with the spectrum, I can choose one which will give me good PAR/PUR for my LUX lighting dollars.

The relationship between LUX and your spectrum graph is what I'm lost on.  How do you relate LUX to the graph? (LUX = the graph with weighting around the 550nm mark) 

Are you proposing that by knowing the formula for LUX and applying the weigthing of your bulb spectrum you could reverse engineer the output levels for each wave-length and then convert that to PAR?  - very interesting idea.

[JetJumper]

Take a look at this on how to make a cheap PAR meter from a LUX meter:

http://www.plantedtank.net/forums/showthread.php?t=179789

[Hookup]

Interesting thread Jet.  I'm not sure I'm following how this conversion/calibration is working.  I've looked thru a few times but its not sticking.  What I can see is that people believe it is working.  So sounds like there is potential to modify an LUX meter and create a PAR approximation meter.

[Canoe]

Thanks for the responses.
Unfortunately, I'm dealing with car issues and a 78 year old friend who's moving, a trailer that needs to be moved and a filter/pump that died, so I'm up to my armpits in alligators.
I'll answer as soon as I have time to give a proper response.
Thanks,

[Canoe]

...So sounds like there is potential to modify an LUX meter and create a PAR approximation meter.

• But you need a PAR meter to calibrate it. If you had access to a PAR meter...
• It would only be calibrated for the lighting setup you have. Useful for checking where to place a coral in the setup you calibrated to. Change your lighting, or the spectrum shifts as the light source ages, and the values will be off - question is, how off?

[bandit]

Woooosh, that's this thread going o ver my head, thanks hook up. I learn something new every day. Tobad now I have fore gotten something

[Canoe]

Are you proposing that by knowing the formula for LUX and applying the weigthing of your bulb spectrum you could reverse engineer the output levels for each wave-length and then convert that to PAR?[/b]  - very interesting idea.

I believe the reason LUX recommendations have been published, is twofold, values have been measured:

• LUX in the wild have been obtained and published. If you're providing a daylight equivalent spectrum, then the lux will get you into the ballpark of light provided at a given depth.
• LUX has been measured for successful aquariums.

Without a lot of calculation, it can only be good to get you into the ballpark, but without a PAR meter or another way to predict what one should get, then you're into purchasing and setting up some rather expensive lighting and seeing what you get.

Spectrum graphs are also known as Spectral Energy Distribution.
Before they're dumbed down for marketing, Spectrums have the vertical axis labeled FLUX. Sometimes they're available. Other times, like with CREE, they strip out the vertical axis, so you can't compare the energy provided in a given range between Royal Blue vs. Blue. vs. Cool White, etc.., just from one wavelength to another for that source. Calculating the area under the curve for two sources, then comparing their published light output, should allow reconstructing a common vertical axis to place the curves on, so their energy output at particular wavelengths could be readily compared.

What I've read says that PAR meters measure all of the light energy in the blue & green wavelength range, of which only a portion are particularly useful for corals, hence PUR meters, which are supposed to measure light energy only at those wavelengths meaningful for corals. (I haven't seen any specs that define either, so I can't see if the PUR also measures up in the 630 to 675 range)
Reading a graph with a common vertical axis would allow one to see how much energy is provided at the wavelengths of interest for various light sources.

With the CBCP (center beam candle power) ratings, angle of beam & width of beam, it is straightforward to calculate the Lux at a distance that matches surface and depth. An accurate Spectral Energy Distribution graph that provides the FLUX, one should be able to calculate values that match those measured by meters of PAR and PUR.

What I see no way of accounting for is:

• light reflecting off the surface
• light absorbed through the water depth of the aquarium, which I also understand varies greatly from one tank to the next.

So, although it expect it could only be dead-on by coincidence, it should get us much closer than "ball park" to predicting what PAR/PUR values we would have from a lighting setup.