# Led lighting issue



## Dave B (Feb 9, 2012)

Hello everyone here at GTA I've join your forum because one of
your devoted members has recommended I search for answers here
after she was unsure of what to do in my situation.
Here's my problem I bought 2 120watt, 20k led banks. The one's
with the 3watt bridgelux leds. The lenses are a 60/90/120 mix.
Each unit is suposed to be the equavalent ta a 250watt Metal Halide
putting out 9520 lummens.
Does anyone know how high I need to have these from the water?
Tank is 18" deep(46 gallon bowfront) and I have a mix of LPS and SPS.
When I first got them I set them at 6" and I think I cooked some of my 
Zoa's that are midway in the tank. Since I have moved the led's up to 10"
Everything seems to be happier, but I'm still a Newbie to Reef setup's
and lack the knowledge of how to tell if a coral is unhappy or not.


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## liz (Jan 16, 2008)

Are they dimmable? If not, then you need to move them up higher - my guess would be about 24"+ as your tank is very shallow. 

LED's are a lot more powerful than you think and your corals need to be acclimated very slowly to them.


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## Dave B (Feb 9, 2012)

Are u saying 24" off the surface of the water or to the bottom of the tank, 
because it's 28" to the substrate and 10" off the water surface right now.


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## altcharacter (Jan 10, 2011)

she's saying 24" from the surface of the water. LED's can be very powerful and under-estimated. Try to make them dimmable if possible so you can adjust the lighting rather than the height.


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## Dave B (Feb 9, 2012)

Wow I never thought they needed to be that high. Thanks for the advice,
I will raise them up. They are not dimmable.


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## liz (Jan 16, 2008)

I have a 20" deep tank, leds are 14" on surface of water and they are dimmed to 50% of their strength - and I am thinking of dimming them to 40%. 

It takes a long time for the corals to acclimate to the led's - weeks! 
So go slow!


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## altcharacter (Jan 10, 2011)

Just my opinion but I would add a dimmer to each bank or possibly link them together. Good luck!


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## Will (Jul 24, 2008)

You can very gradually lower the lights, but it takes a long time for your coral reef to adjust to the high intensity lights. Too sudden an increase and you can expect coral bleaching, soft tissue receeding, algae outbreak.


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## Dave B (Feb 9, 2012)

Thanks all, I've backed off to 20". I'm thinking after them hanging so low for this long
I may shock the stuff that is thriving in the reef as of right now.
Should this also be done in increments given my circumstances.
Also is it possible to add in a dimming switch, the units have 2 powercords and 2 switches. Maybe I can get Nu-tech to mod the units for me.........I'll have to check
it out. For now I've cut back the time the 14k leds come on, and mainly run just the
RB's


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## altcharacter (Jan 10, 2011)

http://www.dhgate.com/led-lighting-...witch/p-ff808081304a25d10130633efc00767e.html

cheap way to do it


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## Dave B (Feb 9, 2012)

Thanks again, I didn't know it could be that simple.


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## liz (Jan 16, 2008)

altcharacter said:


> http://www.dhgate.com/led-lighting-...witch/p-ff808081304a25d10130633efc00767e.html
> 
> cheap way to do it


I think he has to have a dimmable driver(s) in order to dim the lights before he can add a controller? 
I did.


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## altcharacter (Jan 10, 2011)

You shouldn't. The LED should have a minimum voltage it can run off so as long as you meet that requirement you can run it as low as you want. I ran my 8 LED's off 4 AA batteries and a potentiometer to see if it worked and it worked fine.


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## liz (Jan 16, 2008)

altcharacter said:


> You shouldn't. The LED should have a minimum voltage it can run off so as long as you meet that requirement you can run it as low as you want. I ran my 8 LED's off 4 AA batteries and a potentiometer to see if it worked and it worked fine.


Really - I didn't realize you could do that? That is awesome!


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## Dave B (Feb 9, 2012)

i'll give it try and let u guy's and gal's know in this thread how works.


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## Chromey (Sep 25, 2010)

If that works Id like to try it on my Reefbrites.


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