LED Panel

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Adding a LED with the DWL bin code 4, we can flatten the white LED's spectral curve in the 430 to 600nm wavelength range.

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We shall now turn to actual implementation of LED fixtures for the reef aquaria.

Using just two types of LEDs (white and blue) is not sufficient, because such a fixture will miss a significant amount of light in the 400-450nm range - much less than it is measured in the ocean, at the depth of just a few meters. The 450nm spectral range can be easily scaled up by using Royal Blue LEDs with a corresponding peak. 

 

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Fig. 23 shows the spectrum of Ecotechmarine Radion, ReefBuilders 2011 LED 

 

Fig. 23

 

 

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The gap in the 480nm range is properly filled (this fixture uses Cree's blue LEDs). Besides, a small peak in the 660nm range is available. However, any wavelengths in the 400-430nm range, which could promote the fluorescence of many marine organisms, are virtually missing.
This range is missing in the majority of reef LED fixtures. Until recently, no LEDs of proper quality were available in the market for the 420nm range. For the few available offerings the prices were quite high, along with short operation time and poor efficiency.

[sherman]

Many hobbyists tried to use inexpensive no-brand Chinese LEDs in the pure actinic range. However, their efficiency is low and, as a result, the crystal deteriorates quickly due to overheating. Worst of all, this deterioration is hard to estimate visually, since the eye's sensitivity in 420nm range is very poor

[sherman]

We shall now try to estimate the amounts of light at selected wavelength ranges: 400-440nm, 440-480nm, 480-520nm, and 520-700nm. Each range will correspond to one color channel in a LED fixture and can be achieved by using one type or a combination of several types of LEDs.

[sherman]

the 400-500nm range is the most required, since it provides the best coloration and fluorescence in corals; whereas, the longer wavelength radiation in 500-700nm range is poorly utilized by marine photosynthetic organisms. At the same time, the human eye is very sensitive to the 520-600nm range and therefore we do not need very much radiation power in that range: even small amounts of illumination will be sufficient for the eye to perceive the tank as brightly lit. Meanwhile, supplementation of 660nm LEDs can be beneficial for shallow-water organisms. At the same time, this wavelength, in combination with the 400-420nm range, will promote correct rendition of the purple color.

As we have shown, the 400-480nm range is most important for marine photosynthetic organisms. In their natural environment corals are getting 52 to 55W/m2 of optical power in the 400-440nm range and 60 to 64W/m2 in the 440-480nm range.

[sherman]

• Marine photosynthetic organisms most efficiently utilize radiation with the wavelengths around 430nm, and this range also stimulates their most intensive coloration.

We believe that the most reasonable maximum radiation power should be about 45W/m2 for the 400-440nm range and about 40W/m2 for the 440-480nm range. 

To determine the number of LEDs required in a fixture and their rated current these figures must be converted into electrical power, which depends on the efficiency of the LEDs actually used.

[sherman]

If the reef tank is only illuminated in these wavelength ranges for 12 hours, with short sunrises and sunsets specific to the equatorial zone, we will obtain an average radiation power of 400μmol·photons/m2/s, which is sufficient for optimal production of chromoproteins. Since the light fixture is likely to also include LEDs in other wavelength ranges, we can safely assume that these figures include some power margin.

[sherman]

As we have seen, formal parameters such as CRI and CCT are not very useful for determining whether a particular light fixture is suitable for a reef tank. At the same time we need to point out again that sufficient power in the 400-480nm wavelength range is critically important.

We have to admit, unfortunately, that most of the commercially available light fixtures today are only utilizing the 450nm range and above, whereas an ultimately important range between 400 and 440nm is usually left out, or is inadequately represented.

[sherman]

Hope this info can help you in selecting the right light  for your reef tank.

 

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We now know the theoretical aspects of reef lighting, such as the light spectrum and intensity required for growing corals and achieving their best coloration.
We would now like to discuss the various practical challenges one faces when designing a LED light for the reef tank.

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We like to create a light source that would not only good for coral growth but would also yield premium results in the visual perception of a reef tank

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Part One: Planning
When planning for a light source for a reef tank, there are many aspects that we needed to take into account. One challenge is the choice of LEDs that would provide for optimum efficiency. The next challenge is achieving uniform color mixing, in order to avoid unsightly color shades (“Disco” effect) in the tank. Another challenge is how to organize efficient heat removal from the LEDs. Last but not least, we need to “fill up” the spectrum, i.e. which supplemental colored LEDs to use for best visual representation of the corals.

[sherman]

Choice of LEDs 

The specifications of many reef LED fixtures available today are not clear.
Most manufacturers do not specify, the particular LED bins which they used in their fixture.
Bins are a very important characteristic which we need to keep in mind when building a LED fixture.

 

This is number 1 important. Are you getting the best bin or generate bin led?

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What is a bin? 
LED makers sort out their product into several categories, depending on certain characteristics, which they call bins. Color bins contain LEDs with similar wavelengths, or spectrum; luminosity; whereas, efficiency bins consist of LEDs that are sorted out according to the efficiency of converting the electric energy into light. Each manufacturer assigns certain bin codes to these LEDs, and this bin code is attached to LED model number in order to better characterize the properties of the lot that is offered for sale
If we look at the offered color bins, for example, we can see that emitters with different prevailing wavelengths are available for the same LED type. For example, consider the newest generation of Philips Luxeon Rebel ES Royal Blue emitters (Fig 1):

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Fig.1 

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The ability of the human eye to differentiate between close shades of color depends on the range. It varies from approximately 1 nm resolution in the blue-green and yellow wavelength ranges to about 10 nm or poorer for red and blue [1].
It is easy to see that by looking at the bin code.
LED emitter’s peak wavelength can vary significantly. Color bins can be very narrow, sometimes only 5nm wide or even less, and it is important to take this into consideration when we want the whole desired spectral range covered - otherwise we can miss some shades of color in our fixture’s light

[sherman]

The second binning category - luminosity or efficiency bins - is also very important. The manufacturers use this bin type to sort out their LEDs according to the optical power output, while the electric power consumption is the same. Even for the same LED type the difference in efficiency between bins may be significant. Let us have another look at the datasheet of same Luxeon Rebel ES Royal Blue (Fig 2).

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Fig.2 

 

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You can see that the efficiency of electric power conversion into light energy can vary from 37% to 53% for different bins at the same current. This means that the best bin is some 40% more efficient compared the worst bin!

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Thus, by installing less efficient LEDs in a “cheapo” fixture, it will yield 40% less light as compared with the use of best bin LEDs. Yet, at a glance both will seem to be utilizing the same LEDs.
Of course, fixture manufacturers are tempted to use less efficient LEDs, since the best bin’s price can be twice as much as that of the worst bin.

I don't know who like to pay the price of a Lamborghini and get a Suzuki

or you pay for the price of a suzuki and you believe you can get a Lamborghini

[sherman]

Therefore, beware if a manufacturer only specifies that “the fixture is made with Cree LEDs.” without even specifying the particular LED type and the spectrum used - it is most probable that the fixture may be using LEDs which are two or even three generations old, which offer mediocre performance, at best.
The cost of LED emitters is only about 20% of the total fixture cost, but this additional 20% expense can provide up to 40% extra light, and add an additional advantage, less heat generation and power consumption.

[sherman]

There are many other advantages in using LEDs with better efficiency, which are far more difficult to account for objectively due to many unknown variable factors. To name a few, less efficient LEDs will result in higher junction temperature during operation, which in turn, will further reduce their light performance and result in a shorter lifespan of the LEDs. The heat from a less efficient fixture will be transferred to the environment, and it is more likely that the tank and the room will require a more powerful cooling unit.

[sherman]

If we compare low-cost Chinese LEDs, which now flood the market, with the best bins from the best manufacturers, there can easily be three a times efficiency difference, or even more!