Understanding DIY LED Light Spectrum

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Hi guys, I am new here. Very nice forum you got
Here is a really awesome DIY LED thread at an Australian forum I am part of. Please note that this is NOT MY WORK, ALL credit goes to MagicJ @ The Reefuge Marine Aquarium
OK, lets get started.
I am going to try to include in this series of posts as much detail as possible without boring everyone to death. The hope is that by the end you will have enough information to plan and build your own DIY LED light fixture. I don't have a scientific background and will be relying on what I have found on the Net to provide the information. Where possible I will provide a link to the source so the members can read further if they feel so inclined.
There is a huge amount of information available on the net, with varying conclusions. Rather than try to piece together all the differing opinions I have settled on one main reference – a regularly updated article by Carl Strohmeyer published http://www.americanaquariumproducts.com/Aquarium_Lighting.html (last updated 30/6/11). Extracts from this article are provided below. It should be noted this article is published on an aquarium products business site so there may be some inherent bias in the information provided. That being said, I thought that a lot of the information made sense and was based on scientific data.
What Light do Corals Need to Flourish
Photosynthetically Active Radiation (PAR) is the spectral range of solar light from 400 to 700 nanometers that is needed by plants & symbiotic zooanthellic algae.

Photosynthetically Usable Radiation (PUR) also known as "Useful Light Energy" is what concerns us as aquarium keepers even more than PAR in providing correct lighting (yet provides a lot of confusion, especially when considering LED Lights). PUR is that fraction of PAR that is absorbed by zooxanthellae photopigments thereby stimulating photosynthesis. PUR are those wavelengths falling between 400-550nm and 620-740nm.
This is represented in the following graphic.[/SIZE][/FONT]

 

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What LED’s should you use
Many do not seem to understand that not all emitters are equal even with the open source Cree-XR-E emitters, commonly sold for other applications; these are only as good as their correct wavelength output (Kelvin Temperature/Nanometers). One cannot compare a first generation CREE XR-E or similar emitter from a few years back to the newest XR-E of today anymore than you can compare first generation iPhone to the latest iPhone (same name, improved technology).
Based on email I get (some very insulting too), forums I have read, & especially YouTube videos (for DIY LED Aquarium Lights) many people seem to make this very incorrect assumption. This has resulted in a plethora of non reef capable LED lights flooding the market, some claiming to use CREE daylight emitters while in reality these are not even close to the same currently patented emitters used by high end LED lights! I do not know whether to laugh or cry when I read or watch YouTube videos where someone brags how cheaply that they put together a DIY LED Fixture, when in reality this is the same as bragging about making your own PC Computer using a circa 2000 Intel processor and attempting to compare it to a computer using the latest Intel processor!
Another example are the exclusive Cree Emitter bins used by Tropic Marine Center AquaRay/AquaBeam that should not be confused with Cree emitters sold for other lighting applications, as these do not produce the correct Kelvin/Nanometers of Light required for delicate marine reef and freshwater inhabitants and plants. One example is the Daylight Cree XR-E from several generations back that are available to the general public, Chinese manufacturers, and used by manufacturers such as E.Shine or others and sold under USA brand names (such as Marineland). This older generation emitter ranges from 6000 to 9000K and has much more of the green/yellow bands and much less of the near infrared bands of light. Another example is the blue emitter bin used by TMC produces a rather exact 465nm - 485nm (which as per our PAR section of this article is the primary UVA wavelength for optimum PAR). Worse would be the cheaper no name emitters used by manufacturers such as BaiSheng & others and sold under a plethora of other names for so-called aquarium use; these use daylight emitters that can vary from 2000K to 6500K and are in reality totally useless for aquarium use other than just plain light!
There is a reason many cheapie knock offs utilize 100 plus emitters (often 1 watt each), these older technology LEDs use a shotgun approach to achieving aquarium lighting (similar in principle to my use of a dozen low end T12 fluorescent light tubes 30 years ago to achieve adequate lighting).
MagicJ: You can use cheap LED's but you run the risk of not knowing what light wavelength they are emitting. Are datasheets provided? Have the LED's even been tested?
What are Bin's?
/>An example is Intel when they are making a production run of computer processing chips. Some turn out perfect so they sell them at a premium; some almost prefect so they might disable a few of the processors and sell them for a bit less; some might be very bad so they disable a lot of the processors and put them in the discount bin - they all still work but some better than others.
The same thing happens with LED's - the chips are tested following manufacture and coded, or binned, depending on the flux (intensity) and colour.
When looking at any LED, I would be asking these questions:

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  Is a datasheet available
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  Are the LED's sorted into bin's based on flux and colour
  Do you know what bin's you are getting when you purchase the LED's

 

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How Many LED's to Use and What Colour
A few members are starting to put together their own DIY LED builds so I thought it was about time I finished off this 'theory' section of this LED series and got onto the 'good stuff' of actually putting it all together.
I have to say that this topic is very subjective and 100 people will have 100 different answers to the question of how many LED's to use and what colour they should be. There are a lot of variables which will affect the final result such as optics, the type of LED, the type of driver, how the LED's are arranged over the tank....the list goes on. I am going to jump in the deep-end and provide some guidelines but please remember that this is just a starting point for your own research and decision making. The great thing about building this yourself is the ability to change something if required - if you don't have enough light then add some more LED's; if the colour is not right then replace some LED's with different colours.
The recommendations are based on high quality 3w LED’s such as CREE – if you use other types then you may need to compensate accordingly. I have also assumed that the LED’s are driven at around 750ma – if you use a different current level then you may need more or less LED’s. In a future post I plan to discuss the relevant efficiency of the LED’s at different currents.
I think it is fair to say that the old reference to watts/gallon is no longer applicable when applied to LED’s for a number of reasons:

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  The light supplied by the individual diodes is in a much narrower spectrum that that provided by fluorescents or metal halides. We are able to target the required wavelengths much better to meet the needs of our corals without wasting a lot of energy on unwanted wavelengths. This is why tanks with LED’s often do not look as bright as those with alternative light sources.
  LED’s are much more efficient than alternative lighting methods i.e.

Incandescent Bulbs ------- 5-35 lumens/watt
T8 Fluorescent ------------- 80-100 lumens/watt
T5 Fluorescent ------------- 70-104 lumens/watt
Metal Halide ---------------- 65-115 lumens/watt
CREE XPG R5 ------------ 112-132 lumens/watt (based on current from 350ma to 750ma)
Source http://en.wikipedia.org/wiki/Luminous_efficacy
One guideline currently being used is 1 led every 10 to 20 square inches (65 to 130 cm2) – 10 square inches for SPS dominated etc (400w MH equivalent), 15 square inches for a general reef tank (250w MH Equivalent), and 20 square inches for lower light inhabitants (175w MH equivalent).
This results in the following numbers for some common sized tanks:

Some adjustments to these numbers will be required to fit the capacity of your drivers but it is a starting point. I also feel that these are the maximum number that would be required - I have 60 on a 4x2x2 but have then located where my corals will be as I see no sense in lighting the weir, or the back of the tank. Careful placement can reduce the number of LED's used, and money.
Now that we have the numbers sorted, what colours are best?
For a few years now most LED lights have used a combination of Cool White and Royal Blue.
As a general guide:

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  1 Royal Blue to 1 Cool White => 10K – 12K
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  2 Royal Blue to 1 Cool White => 14K – 16K
  3 Royal Blue to 1 Cool White => 17K – 20K

Relatively recently there has been a lot of discussion surrounding the spectrum produced by this combination and there is now a school of thought that using a combination of Cool White, Neutral White, Royal Blue and Blue provides a much better coverage of the required spectrum especially as the Neutral White provides more of the red spectrum.
We have previously discussed the required wavelengths utilised by corals as falling between 400-550nm and 620-740nm. As an example, this is the mix I am currently using (CREE LED’s)
XPE – Royal Blue D40 455-460 nm
XPE – Blue B30 465-470 nm
XPE – Blue B40 470-475 nm
XPG – Cool White 0D0 R4 Approximately 8,300K
XPG – Cool White 1C0 R5 Approximately 7,000K
I am using 50% white and 50% blue which appears to give a colour equivalent to 16K, when compared to my previous 14K MH bulbs. Whilst I am generally happy with the light produced, purple and red corals do not look as good as I would like and I am considering replacing some of the Cool White LED’s with some Neutral White and Purple.
Some people are also experimenting with the use of other colours such as red, green and UV LED’s.
Hopefully, this will give you a guide to start your own deliberations. There is no right or wrong answer and everyone’s requirements will be different depending on your tank and its inhabitants.