just out of curiosity sake do you know what MH and T5 fixtures are lumens/watts?
It's not relevant to use lumens/watt to compare different types of lighting when working with reef tanks. More on that below.
I'm looking into getting a parts bundle from him without any whites and order in my own CREE or XRE to place into the array, DWZM is this a good idea? Another thing I was planning on doing is mounting them to a real Heatsink from heatsinksusa.
Efficiency of blue LEDs is often overlooked in these threads, but to a coral, it's absolutely important, easily as important as the whites, so IMHO you should make the same quality/efficiency choices on both colors.
As far as the heatsinks, I actually think the "fan blowing down a tube" idea is pretty interesting, so I wouldn't discount it at face value.
wikipedia says 65-115 for "metal halide", a large range just the same as if you were to compare any number of "high power LED" and include low-end (63.3 like these) to high-end (130 in a cree xpg).
Again, not a relevant comparison.
something is not adding up. according to der_wille it seems that steves Leds are no more efficient then MH? I find this very hard to believe.
Broken record: not relevant! see below.
Bummer,
I was really rooting for the underdog in this one
I was hoping an actual data sheet would pop up and prove a few people here wrong, no such luck. Ah well they are probly still a decent cheap alternative.
Cheap in terms of upfront cost. If you have a small tank, or one you're not planning on keeping more than 4 or 5 years, or you're figuring you'll upgrade lighting in the near future, these LEDs might still be a reasonable alternative to higher priced LEDs. Keep in mind that two or three years ago when the first people started playing with HP LEDs on fish tanks, this was about as good as it got. Again, I do not intend my comments in this thread to read like I'm saying these LEDs are crap, or useless, but rather to try to provide a realistic comparison between these and other commonly used LEDs.
This is a very interesting read. I am starting to play with the idea of switching my tanks to led light. I am going to start with a light for my fuge. ( currently lit by a 175w MH tar ballast and a cheap 10K bulb) thinking 24 white led.s should do the trick.
I have some questions about these led's that may have obvious answers but not to a led beginer like me.
In the data sheet it shows using 130 deg viewing angle (lense?) Steve stated his are set to 90 deg.
1.How would this affect the lumens measured?
2.what is the viewing angle of a "standard" cree?
3. Is lumens a measure of total light output or light measured at some point
Steve, no not that Steve
Steve, and others with general questions like this, IMHO you really would be best served looking at the links above. Most of your questions have been answered already, and you're more likely to get a complete and reasonable answer by reading what's already been stated rather than relying on people to repost it in this thread. That said - starting with a 'fuge might seem reasonable, but keep in mind few people have used LEDs for macro growth, so we don't have a solid grasp on the best colors/models to use for that purpose. By all means experiment and report your findings, but keep in mind that results on a 'fuge won't directly translate to results on a reef tank. Regarding your numbered questions:
1) The "viewing angle" of a bare HP LED is essentially the full width angle of it's output beam. Imagine two LEDs with the same absolute output, but one with a narrow viewing angle and the second with a wide angle. The one with the narrow angle will
appear to be more intense if all you think about is light directly below the LED. However the one with the wider angle will cover more area. In a very large array, the difference more or less disappears. In a typical fish tank array, you'll see the difference. That said, since many of us put optics on our arrays, the difference will be moot, since the final beam witch is determined by the external optic.
2) No such thing. Out of the Cree LEDs commonly used for fish tanks, there are a variety of viewing angles. XP-G are 125. XP-E are 115 or 130, depending on color. XR-E are 90 or 100 depending on color.
3) Lumens is a measure of absolute output, i.e. accounting for every photon leaving the luminary. It's not directional. So, an LED with a 130 degree viewing angle and an LED with a 90 degree viewing angle that are both rated at 100 lumens produce the same amount of light - the difference is in where that light goes. (See notes below on lumens though, because - again - we need to be careful how we use the term when comparing luminaries).
I'm guessing the relatively small viewing angle of Steve's LEDs contributes to their anecdotal success in the tanks we've seen in this thread. It's basically like taking an XP-G or XP-E (the two most commonly used Crees these days) and putting a really wide optic on it, which in many situations, results in more
apparent output, since more of the light is being made useful within your tank.
If you put 250w of LED's in a same size pendant as most MH's it would get pretty hot too... but LED's have no IR radiation so it doesn't heat up the water through IR. I'm sure someone else can elaborate more on this subject, but that's my take from what I've read.
More or less correct. When talking thermal matters, LEDs dissipate most of their waste as heat conducted physically out of the package through the substrate ("star" board) to a heatsink. MH gets rid of it's heat via invisible radiation. On a fish tank, the LEDs' heat is "easier to deal with" since we can blow it out of the canopy with a fan, vs. let it radiate on our water/corals/sandbed/etc and heat them up.
Let's not forget the huge relative loss in efficiency when comparing a metal halide reflector to an LED lens. Most LED lenses specify that they are ~85-90% efficient at directing the light, whereas halide reflectors are something like 70% efficient, so the disparity in efficiency between halide and LED grows even more when this is taken into account. Beananimal helps to illustrate this point in my build thread, if you want further reading on the subject.
Yes, and it's even more extreme when you consider that an LED doesn't NEED an optic. It's inherently
very directional compared to MH, fluorescent, etc. Right out of the box, you have 100% of the light going in a relatively narrow cone. Compare that to an MH lamp, where light radiates in all directions. If you put both sources of light over a fish tank with no reflectors or optics, the percentage of light from the LED that makes it into the tank will be very high. The percentage of light from the MH that makes it into the fish tank will, mathematically, ALWAYS be less than half. Add a reflector to the MH, and you might get somewhere between 50 and 75%. Add an optic to the LED and you can be within spitting distance of 100%. So, as I mentioned in a post above, even if you had an MH that was "more efficient" than an LED, the LED could prove "more efficient" in real life, since less of it's output would be wasted.
Regarding lumens - and repeating what I mentioned above - lumens
specifically measures light in a "weighted" curve, because it's intended for use when comparing apparent intensity to the human eye. In the absolute sense, this is pretty much useless on a fish tank, because we care about light that is photosynthetically useful, not just visually useful. It would be possible to have two light sources with the same lumen rating, but one is nearly useless on a reef tank while the other grows corals like mad. Hence, you CANNOT compare two sources of light JUST based on lumens and make conclusions about usefulness or "efficiency" on a reef tank. You MUST consider spectrum as well (or switch to a meaningful unit like PAR).
So, let's take a few scenarios. Say we have two "cool white" LEDs. We know from their datasheets what the spectral plots look like - they're almost the same. We know from their datasheets that LED A does 100 lumens/watt, and LED B does 50 lumens/watt. Since we know that they have the same spectrum, we can deduce that, in reefkeeping terms, LED A is "twice as efficient."
Now, let's consider the same LED A, and an MH lamp that does 100 lumens/watt, but has a vastly different spectral plot. We CANNOT deduce that they will have the same "efficiency" or effectiveness on a fish tank! At least, not without either a careful comparison of their spectral plots, or gathering of more information (PAR readings).
So, to repeat, lumens is fine to use if we know the specrta of the luminaries we are comparing are the same. That's why it is appropriate to compare two cool white LEDs, for example. However, it's NOT appropriate to compare luminaries with vastly different, or unknown, spectra, which is why we should not use lumens to compare an LED array to an MH or T5 array, for example. If we want to make those sorts of comparisons, PAR is probably more appropriate, though likely still not perfect.
