DIY lighting coverage question

[childress5tyler]

In the near future (within two months), I will be upgrading my 34 RSM to an 80 gallon deep blue rimless tank (48x24x17). While preparing to upgrade, the question of "will my current lighting fixture be sufficent" has come up. I have a very, very good DIY LED fixture and am 75% sure it will be more than sufficent enough to support and cover an 80 gallon tank with only two slightly "dark" spots. I plan to hang my fixture approximately 8-12 inches above water.

My current DIY LED Fixture:
20" heatsink
- 8 3 watt Cree Cool Whites
- 14 3 watt Cree Royal Blue
-3 3 watt Cree Blue
-4 3 watt Cree UV Violets
-2 3 watt Cree Reds
-1 3 watt Cree Green

all of these lights are dimmable, so my question to you all is do you think this fixture will cover such an aquarium? Thank, and I look forward to hearing your responses.

 

[fragmatic]

I too have some DIY cree units. You are going to get opinions all over the ball park. To my experience with cree fixtures you do have enough LEDS and a decent selection. But, I have a problem with the 48" length. UNLESS, you concentrate the coral in the center and use the outer ranges for corals who like less light. So this IMO is an aquascape consideration. I'm keeping coral fine in a 90 that is 23" deep x 26 x 39. I am running 54 watts of LEDs but my fixture is 36" long. Don't get too caught up in the wattage numbers game. Wattages just to not seem to describe LED effectiveness as well as we would like to believe IMO. My take is this: Try it and see how it goes. At worse case scenario you build another mate to the one you have.

 

[childress5tyler]

I'm hoping that if I hang it in the perfect position I can cover the entire tank. Do you think its possible to cover it all?

And I suppose I could build another fixture if it didn't work out at first.

 

[fragmatic]

I'm hoping that if I hang it in the perfect position I can cover the entire tank. Do you think its possible to cover it all?

And I suppose I could build another fixture if it didn't work out at first.

It depends on the lenses you used. The last time I reworked my fixtures for a different tank (a frag tank) I tossed out the lenses and I like it much better. I think you may reach the whole tank at a few inches above the sand but PARs will be lower at the ends. Which is good for some corals. Or you can crank it up a bit and be careful how slow you bring corals to the center top. Still I'd start with the settings you were using before and make VERY slow changes. My two cents worth.

 

[childress5tyler]

Thanks for the responses. I guess I should have add in that I do not have optics on my LEDs

 

[Dave A]

I'm thinking you'll come up short, especially at the ends. The general rule of thumb is that you need roughly one 3 watt LED for every 15 sq in of surface area, up to 24" deep. This allows some "fudge factor" since nobody runs their emitters at 100%. My "best guess," without knowing more, is that you should probably add a few more LEDs to the current heatsink, and then build a second one. For reference, I'm running 66 XT-Es and Luxeons over a standard 90 (48x18) with 90 degree optics and it doesn't seem like overkill to me.
A few questions;
1) Which Crees? XT-Es put out more light per watt than the previous generation, which put out more light than the 3 watt Crees before them, etc.
2) Cree UV Violets? UV and Violet are two different things and, last I heard, Cree doesn't make either of them. Are they something new?
3) How much current are you running?

 

[childress5tyler]

1) yes they are XT-E

2) at reefledlights.com they were labeled as 'UV Violets' and I'm 90% sure Cree made them but could be wrong.

3) not sure if I completely understand the question

 

[Dave A]

1) XT-Es can run at up to 1500mA with a Vf of a little over 3V, so technically, they are 5 watt LEDs. I wouldn't actually put 1500mA into them, they wouldn't last very long, but you should be able to safely run them at at least 1A.
2) The "UV Violet" LEDs are not made by Cree. That product is probably made by Epistar, it has an output of 410-420nm (peak at 417nm) and has a maximum current of 700mA at 3.5V, this would be a 2.5w LED. This is one of the better Violet LEDs out there and is just that, violet, not UV. Wavelengths below 400nm are considered UV and are not visible to the human eye, Violet is the part of the spectrum from 400nm to around 430nm, the human eye can "see" this light, but it is not very sensitive to it so the LEDs appear dimmer than they actually are. It is said that these emitters can be run safely near their max current, YMMV. These also appear to me the same ones as those sold by Steve'sLEDs, I have 10 of them over my 90 gal and wish I'd used a couple more.
3) what drivers are you using and what is their current output? You cold run your XT-Es ni a ELN-60-48 at it's max current (1300mA) and get nearly the maximum light output from each LED, or you could drive them at lower current and get less light from them. If you are running them at 1000mA (for example) you will not get the same amount of light. Efficiency varies with different current levels so you will not get twice as much light by using twice as much current, but since you are hoping to use fewer emitters than would usually be considered "enough," it would be best if you are getting as much from them as you possibly can.