Re: [APD] LED lighting

["Bill Wichers" <billw at waveform_net>]

All the high-power LEDs need some type of heatsink to keep them from
overheating. Many of the higher-power LEDs are actually internally
constructed on a ceramic substrate to allow for high operating
temperatures. You don't run into the heat issue with the smaller LEDs
due to their much lower relative power levels.

The heatsink issue isn't usually a big problem to deal with if you're
using the middle-power LEDs. Some of the really big ones (there are some
90 watters out there!) need specialized cooling, but the moderate ones
tend to be more DIY-friendly. I've constructed some fixutures by just
mounting the LED elements to a heavy aluminum sheet 1/16" thick and
that's been sufficient. 

If you go the DIY route there are two things to remember:

1 - You really need a current-regulated (basically a constant current
source) power supply. Most supplies are setup for constant voltage
applications are not ideal for use with LEDs. The big reason is that as
the voltage increases an LED will want to draw more current, which tends
to increase the heating within the LED which leads to:

2 - LEDs draw more current as they get hotter. Hotter means more
current, more current means hotter, and then you get into a thermal
runaway situation which will result in the failure of the LED.

Best practice is a constant-current power supply and a series string of
LEDs. There is lots of info out there on how to construct the power
supplies. You can make a very basic, but not very efficient, linear
supply with an LM317 regulator in constant-current mode or you can use
one of the more advanced and much more efficient switching controllers.

  -Bill

> I'm currently fishless, and one of the things holding me back from
setting
> up my new tanks is that I don't know if I should go with the
fluorescent
> AHW setups I have or push on the LEDs.  My main concern is to be able
to
> grow plants with moderate light requirements (not the really
high-light
> plants) while not overheating the tanks, especially in the summertime.
> 
> I was reading some DIY information about LEDs, and it mentioned a
> requirement for a heat sink.  This is not something I'd anticipated
based
> on minimal experience with small LED stick-on lights or keychain
lights,
> and I'm wondering how much heat those powerful enough to light a 12 to
18
> inch deep aquarium put out.
> 
> Diane in Los Angeles
> 
> http://debunix.net/fish/fishIndex.html


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