What is the output of you LED fixture?

[tydtran]

I know very little about LED's, so forgive me if I am asking something that has already been discussed.

I want to try LED on my 40 breeder, with the goal of growing sps. I found an LED fixture that is usually sold to people growing greenhouse plants. 72 white and 36 blue LED's with a power consumption of 48 watts and light output of 3800 lux.

For people who have built their own fixtures, what ratio of lux to watts are you getting?

[tydtran]

I always read about how efficient LED's are. For the fixture above, at 1 meter the above fixture is putting out 3800 lumens. For comparison, a 250w metal halide would put out 25000 lumens. Lumens/watt would favor the MH, right?? Is it just that this fixture uses some sort of inefficent LED. Are you guys using a more efficient LED in your builds?

[der_wille_zur_macht]

First of all, that fixture is likely total junk. There are LOTS of bad LEDs out there. Consider that a really poor LED might produce 10 lumens per watt consumed, and a really good LED might produce 150 lumens per watt consumed. Clearly, there's a lot of room for variation.

Secondly, it sounds like you are confusing terminology - you're using lux and lumens interchangeably, and you mention lumens at a certain height, which doesn't make sense, because lumens is a measure of all light emitted, not just light incident on a certain surface area, which is basically what lux measures. In other words, height doesn't change the lumens produced by a given fixture, but height and angle would change the lux.

Plus, lumens is really not appropriate for comparing light sources with different spectra (i.e. LEDs to MH) because it's basically weighted spectrally according to how the human eye perceives brightness, which is different than how a fish tank uses light. So, a light source that produces 1,000 lumens might be much better for our reef tanks than one that produces 10,000 lumens, for instance. Despite this weakness, lumens IS useful for comparing light sources with very similar spectra, i.e. comparing two particular brightness bins of a given model of cool white LED.

In the anecdotal sense, most people who have recently converted from MH to LED have found that their LED rigs can be built to consume around 1/3 - 1/2 the power they needed for an MH fixture, to end up with a similar result.

[tydtran]

Thanks for chiming in DWZM. I was typing quickly and left out some words. For the 3800 lux fixture, I meant to say that the output was 3800 lumens/m^2.

So there are LED's of different efficiencies. How can you tell which ones are most efficient?

[TheFishMan65]

You have to read the datasheet to see the efficiency. Right now Cree are the most efficient.

[der_wille_zur_macht]

Unfortunately, vendors selling completed fixtures rarely if ever specify the exact model and bin of LEDs they use, much less provide datasheets for them.