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post #5 of (permalink) Old 07-05-2012, 05:39 AM Thread Starter
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Join Date: Aug 2009
Location: Vancouver, WA, USA
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5. Emitters

What am I looking for?
You should start by figuring out the right number of emitters in the best layout to provide the most even PAR coverage in the largest volume of your tank. LEDs emit light in a cone, so the closer to the emitter, the smaller the area lit. (See Optics for more info on beam angle.) The PAR may be different for each individual emitter of the same type depending on binning.
Emitter Data

These are links to the manufacturer's data on some popular LED's. For the Cree website, the LED model page contains a link to the data sheet.
Cree XT-E
Cree XP-G
Cree XM-L
Cree XP-G2


Bridgelux BXCD 45
Bridgelux BXCD 50
Bridgelux BXCD 60


Luxeon Rebel

Important specs to know about your Emitters (in no particular order)

Color temperature
Max Current
Forward Voltage
Flux or approximate PAR
How many for my tank?
Hoppy has done a lot of the hard work for us in this department. Here is a link to his thread, which includes a Microsoft Excel Calculator to determine how many of a particular emitter you need to provide adequate coverage for your tank. The most updated version of the calculator is attached in post #14.

Here is some info from Hoppy on how he uses the calculator:

Originally Posted by Hoppy
How to use it, depends a lot on how you want to use it. Here is how I use it:

I start with the last calculator section, the one that as the notes at the end. Then I figure out how far from the substrate I want the LEDs to be, and enter that as "LED height (inches). Then I assume how many rows of LEDs I will want to use, and enter that as "Number of LED rows". Next, I decide what I want the maximum PAR to be, or if a non-dimmable driver is to be used, what I want the actual PAR to be, and enter that as "PAR (micromols). If the light is to be several inches above the top of the tank I will decide if I want to use 40 or 60 degree optics, and enter that number as "Cone angle (degrees). I estimate how many LEDs I will use, and divide the tank length by that to get a guess at "LED spacing (inches)". With that, if i click on one of the final rows, to make it calculate, the calculator will give me how much LED current it will take using each of 4 options for LEDs. Look at the LED model I plan to use to see if the current is what I want to use, which is about half of the maximum current for the LED. (You may want to use other criteria for what current you want, but with a non dimmable LED, it should be the current the driver puts out. Now, it is just a process of iteration - change a variable, like LED Spacing, and see if the current for the LEDs I want will produce that PAR. I try it with a different number of rows, up to 4 maximum, and see what that does. I look at the other LED models to see if one of them would be better. Etc. until I decide I have a combination of parameters that suits me best.
Originally Posted by Hoppy
One more thing: that calculator has a couple of quirks. The biggest cone angle you should put in for a Cree XM-L is 72 degrees - use that until the optic cone angle is less than that. The biggest cone angle you should use for a XR-E is 48 degrees, and until any optic, if there are any for that older LED, cone angle is less than 48 degrees, just use 48 degrees. I don't know why that works that way, but it does.
What colors do I need?
Color temperature is largely a matter of your personal preference, but some suggest that selectively combining particular color temps will provide better growth. Remember that the colors we perceive in the plants are colors that ARE NOT absorbed and used for photosynthesis, so eliminating these colors will make your plants look gray and drab, though they may yet be healthy. Remember that color temp preference is largely based on PERCEPTION, and is very subjective.
White emitter colors typically fall into three categories: warm, neutral, and cool. Warm is a lower color temperature that appears more amber or yellow in color, neutral appears natural and balanced, and cool provides a higher temperature bluish look. It has been said that natural light is closest to about 3500K (we have a “yellow” sun). For a good balance of plant health and aesthetics, some choose a combination of 6500K (cool white) and 4500K (neutral white) emitters. Others prefer a “crisp” or bluer look, and add 10,000K or “Royal Blue” to the mix. Some vendors offer more specific color combos, but these lead to their own challenges. (See “What is the disco effect?” for more info on these challenges). Ultimately, the choice is left to individual preference.
Here is a link to spectral data for some different emitters.
Does it matter which brand I get?
Ok, well, let’s address the loudest voices first.

1. There will always be “fanboys.”
2. Most (if not all) LED’s are produced in China.

These are facts of our global economy. Ultimately, you will choose the emitters that satisfy your needs best. Cheap? eBay. Midrange price? Aquastyle carries Bridgelux LED’s for $2.50 each, shipping not included. Steve's LEDs carries Phillips emitters for a similar price. Popular brand name? Crees are widely available and well documented. Remember that price is determined by production costs, shipping, and market demand. If it’s cheaper, there is likely a reason (though this does not necessarily mean they are crap). The most important element: Be sure you are comfortable with that compromise before you buy.

Last edited by theblondskeleton; 07-16-2012 at 06:35 PM. Reason: Added XP-G2 link
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