PAR and LED light composition

spoggy · Feb 11, 2014

For all intents and purposes, PAR in a reef aquarium refers to the photosynthetic active radiation between 350-750 nm. If this is true, and we're measuring with an Apogee meter (for sake of discussion), what PAR value is assigned to each individual color of LED to make an aggregate PAR? I mean we can run all blues and get a PAR of 500 or 600 at the top of the tank and 200 at the bottom of the tank. Similarly, we can move to all green, reds and whites and get the same type of PAR readings. Obviously, neither of those are the best for keeping corals. How are LED users adjusting their individually colored LEDs to get an aggregate PAR? I am currently running a AI Hydra 52's, but this can apply to any fixtures, whether store-bought or homemade that has multiple colors of LEDs in the unit.

TJ's Reef · Feb 11, 2014

There really is not a concise or simplified rating of LED's and why it only can be used as general reference. And why it is rough at best when comparing to MH or T5's that can have significant amounts of light measured by PAR readings that have little value in a Reeftank. We must either educate ourselves or trust that Company 'X' will provide the correct blend of emitters for us. We know basic requirements as far as spectrum goes for our coral to be able to metabolize nutrients through photosynthesis but each species and even same species at different depths has varying strains of symbiotic algae adapted to specific spectra. PUR is/would be a better value for this but not a very affordable or available format of instrumentation for us.

Cheers, Todd

spoggy · Feb 11, 2014

So, I won't trust that any company would provide us with the information that we actually need. And unfortunately, you are correct that the instruments that we would need at the hobbyist level are entirely too expensive for many of us. But, given what we do have, we should be able to make some educated guesses with respect to PAR from certain emitters versus PAR from, say natural sunlight or metal halide or T-5's etc. More so than any other lighting source, we can't depend on what it "looks" like to determine whether or not it's healthy for our coral. I don't know if there is, but I'm wondering if there's information that says "in the 350-750 nm spectrum, royal blue makes up this percentage of the light and you can duplicate that by a setting in an emitter to X value versus the other emitters in the array." I'm surprised that Sanjay hasn't done something like this yet.

Steve

ReefLEDLights · Feb 11, 2014

I swag a 10% under rating for a fixture with mostly 450nm Royal Blue

This link may help and is more scientific. There is also a link to some work by Sanjay Joshi which is a good read

http://www.apogeeinstruments.com/aquarium-par-meters/

Bill

Ron Reefman · Feb 12, 2014

Steve, it sounds like you are looking for information something like this?

Or this?

But just doing your lighting for the health and growth of your coral and it's zooxanthellae shouldn't be your only consideration. You want the corals to look good as well. And the better the 'full spectrum' your light is, the better the corals will look. You need everything from 400nm to 700nm so it can reflect back to your eye and allow you to see the 'true' color. Our current 'multi spectrum' led fixtures, especially with the poor CRI white leds isn't as good as we might like it to be. But better CRI whites are still 20 times more expensive than the cheap whites in use today. So the switch to good CRI whites would increase the cost of a fixture by $200 at the low end and maybe much, much more.

TJ, there will probably never be a meter for doing PUR (Photo-synthetically Usable Radiation) because every algae and plant have different wavelengths they can use, so you'd have to know what the plant can use before you could set up a meter to measure that PUR. A PAR meter designed for use with corals that is set up to measure the more typical wavelengths that coral's zooxanthellae use (400nm-480nm and 650nm to 680nm) would be a lot more accurate for our needs, but I'm not holding my breath waiting given how much the Apogee meters sell for. On the other hand, I still find my Apogee meter is a very useful tool despite it's flaws related to what I use it for.

spoggy · Feb 13, 2014

https://tests.capnhq.gov/ops/archer_training/archer_hsi_tech/Spectroscopy.cfm

The section under "Measuring a Spectrum" is more of what I'm after. Not only does light have frequency, it also has amplitude. For the 7 emitters in a Hydra 52, there should be a way to match the frequency to that of natural sunlight in, say Figi, or the Marshall Islands and determine the amplitude of each to produce the best quality for light for corals from those areas.

ReefLEDLights · Feb 13, 2014

The type or spectrum of light the corals receive in their natural environment is often very different from the light most "Full Spectrum" fixtures provide.

It really depends on the depth the coral.

For example Red is blocked by the first couple meters. Corals at medium depths receive virtually no Red.

Bill