In our previous article we considered 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 high bay light for sale for the reef tank .
Over one year has passed since the publication of our first publication on reef lighting. We planned to publish our second article on practical aspects of building a LED fixture shortly thereafter. At the time, we were actively working on the design of a special LED assembly that, based on our understanding of reef lighting requirements, would be best suited for a reef keeper's needs. However, we decided to postpone the publication, until our ideas fully matured based on our actual achievements.
As our work progressed, we decided to share not only theoretical stipulations, which were our starting point, but also the experience we gained through the efforts towards creating a light source that would not only provide for good coral growth but would also yield premium results in the visual perception of a reef tank.
The first part of this article describes how we planned our LED assembly; in the second part we describe our progress, in several successions, towards the latest version of our product.
We hope that our practical achievements, the problems we encountered, and our attempts at solving them will prove useful to the reef keeping community.
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, ie which supplemental colored LEDs to use for best visual representation of the corals. We shall consider these challenges in detail in the subsequent sections.
Choice of LEDs
It is evident that, whenever possible, preference should be given to LEDs manufactured by one of world's leading manufacturers: either Cree or Philips - they provide the best efficiency among commercially available LEDs today.
The specifications of many reef LED fixtures available today list the brands and types of LEDs used (such as Cree XT-E or Philips Luxeon Rebel). Yet, most manufacturers do not specify, the particular LED bins which they used in their fixture. Still , bins are a very important characteristic which we need to keep in mind when building a LED fixture.
What is a bin? Due to technological reasons, the parameters of LEDs can be different even within the same batch. To achieve a product with uniform quality, leading 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 Peak wavelength bin structure for Luxeon Rebel ES Royal Blue emitters
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.
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 Radiometric power of Luxeon Rebel ES Royal Blue emitters at 350 and 700ma, depending on luminosity bins
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!
Thus, by installing less efficient LEDs in a "cheapo" fixture, it will yield 40% less light compared with the use of best bin LEDs Yet, at a glance (and even according to fixture specification - if bins are not mentioned)., 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 (besides, LEDs of topmost quality are scarce; they are usually not readily available for purchase and "catching "the best bin requires significant efforts from the fixture manufacturer).
. This concerns the LEDs of same type Price (and efficiency) difference between different LED generations is way higher Therefore, beware if a manufacturer only specifies that "the fixture is made with Cree LEDs." Without even specifying the particular LED type 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.
Unfortunately, manufacturer's interests do not always match that of the user. 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. If we consider a 300W LED fixture as an example, calculating for 12H daily operation, and based on a 15c per kWh power cost, the total power consumed in 10 years of operation will cost (300/1000 * 12 * 365 * 10 * 0,15) = $ 1,971 for a fixture with the worst bin, while the owner of a fixture with the best bin would save $ 788 throughout this period.
There are many other advantages in using led high bay light for sale 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.
So far, our estimates were based on a 40% efficiency difference between the best and worst LED bins of the same type. Depending on the LED type, this difference can be higher or lower. If we extend our speculations and start to consider LEDs from different manufacturers, this efficiency difference can be much higher. 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!
In fact, this means that by choosing between two fixtures of same power but a three-times price difference, one may to yield less light per dollar from the cheaper fixture (this is true under the assumption that the fixture cost is directly linked with the cost of used materials rather than other marketing factors). At the same time, the less efficient fixture will spend much more in power bills in a fixture's lifetime.
Worst of all, it is almost impossible to accurately measure LEDs efficiency at home, and manufacturers are tempted to indicate a higher efficiency for the LEDs they use: serious errors in LED fixture specifications are common.
We believe that the choice of most efficient LEDs is very important when building a fixture. As we have shown, their higher cost will be justified in time.
There are a few other important issues which are often poorly addressed in existing fixtures.
We have heard claims from many experienced reef keepers that LED lighting has not yet matured for aquarium use We believe that this notion is caused by two main shortcomings of the existing fixtures:. Spectrum deficiency and poor color mixing which results in multicolored blotches and shades.
The first problem is relatively easy to address by combination of different LEDs in order to cover the desired spectrum fully (in our previous article we have shown that violet spectrum plays an important role but is neglected or poorly represented by most manufacturers, mainly due to the high cost).
The second problem requires a complex of efforts to achieve an acceptable solution. Some people spot these color blotches at once, while others may require time to notice the problem. Still, it is very important to eliminate this effect, as it affects our perception of the reef tank directly.
Challenge number one: Getting rid of color shadows (disco effect)
The so-called disco effect is witnessed when a tank is lighted by several power LEDs (especially multi-colored) which are positioned on a certain distance between each other. Each LED is a point light source, resembling a small sun. When illuminated by several LEDs from different directions, every object produces multiple shadows. When these LEDs are of different color, these shades look colored like disco lights.
The only way to overcome this effect is to place LED crystals as closely as possible. We cannot place all the LEDs of the fixture in one place, as we want to light up the whole surface more-or-less uniformly. Therefore, we need to gather all differently colored LEDs in groups, in the required proportion. These groups can then be evenly spread over tank's surface.
One option is to collect a group of LED crystals in a small space by creating a custom COB (Chips On Board) with many LED crystals closely packed in one case. A COB is a matrix of individual LED crystals attached to a common platform and covered by a protective compound (usually silicone) They have several advantages over SMD LEDs and are becoming quite widespread for general lighting use Indeed, they are easy to mount, provide a relatively low cost per emitted light, and are undemanding to optics -.. they are, indeed, very good when you need lots of light from an inexpensive fixture. COBs can be very good for the lighting of roads, warehouses, or other large premises.
Custom COBs can provide a perfect color mix if crystals with the right spectrum are selected However we believe that COBs are not the best choice for a reef tank Three factors are most important when building a reef fixture:.. Spectrum, efficiency, and optics.
In theory, a COB may contain any crystals. However, none of the top ranking manufacturers, neither Cree nor Philips Luxeon, cover the whole spectral range required for reef lighting. Cree, for example, does not make violet ("true actinic") ., or deep red LEDs, Philips Luxeon also doesn't cover the violet range Of course, there are smaller companies which make a wider range of LEDs, and their crystals cover the required spectrum However, our second requirement -. efficiency - would suffer . Theoretically, crystals from different manufacturers can be combined in one COB package, but this can be practically impossible for similar crystals, made by different brands. As a result, the COB will have to use crystals with significantly lower efficiency, compared with world's leading manufacturers Our calculations based on the datasheets from leading Taiwanese manufacturers -.. Epistar / Epileds, show that there can be as much as 54% difference in efficiency compared with best individual LEDs from top manufacturers Besides, manufacturers usually don't put their best crystals into COBs. Even Cree declares about 34% less efficiency for their best COBs today, compared with individual LEDs.
A shorter thermal path in COBs is usually listed as an advantage, however, this is not as simple as it seems. As an example, let us consider Cree's newest COBs. As one of World's top leaders in LED technologies, this company pays closest attention to improving the thermal characteristics of their products. According to the datasheets, thermal resistance of Cree's COBs varies from 2.5 ° C / W for CXA1507 to an impressive 0.8 ° C / W for CXA2530. Seems to be pretty good, huh? Only until we notice that, say, CXA2520 may consume up to 50W of power. According to the datasheet (see the picture below), this will add a significant 40С to junction temperature above the temperature of the LED case. For CXA2530, with 61W power consumption, junction temperature will be even higher.
More info you can visit:http://www.lead-lighting.com/products/sid22-1.htm
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