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Re: [APD] LED Lighting

Andy and Scott,

Message: 2
Date: Mon, 29 Dec 2003 09:17:15 -0800 (PST)
From: "S. Hieber" <shieber at yahoo_com>
Subject: Re: [APD] LED Lighting
To: aquatic plants digest <aquatic-plants at actwin_com>

There's nothing to stop one from using the new super bright
LEDs for lighting a tank.  There are a varitety of color
temps to satisfy diff tastes. The problem has been the cost
of the LEDs and the assembling a suitable array of the
devices to light a tank.

It is a great idea, and gives us an ability that has been difficult or impractical with other lighting -- immerse the lamps! This will bring a whole new era of illumination design to planted aquaria. I have just been coasting along, waiting for prices to drop a bit more.

It's not impossible to make such an array, just a pita. And if one doesn't get the voltage right, the LEDs burn out very quickly.

Voltage isn't a good thing to set. The diodes will develop a certain voltage for a given current, and current regulation is more certain to not overdrive them in most cases. The Wattage and light output track current very well, but the voltage is low and is not changing very much over a wide range of currents.

[It is exactly analogous to using a needle valve to control the flow rate of CO2 and not a pressure regulator (that allows any old flow rate), like an Eheim check valve.]

Try running them at a bit below the rated level. If you use diff colors (red, blue, green), then put the diff colors on different circuits back to the power supply -- the reason is that diff colors heat up and draw current at diff rates and the LEDs will tend to last longer if you yu keep them separate.

Again, each kind has its own *current* needs, so for crying out loud don't put each on a Voltage-regulated circuit! Drive them with the collector of a transistor, and regulate the current through them, not the Voltage across them, which varies with doping, temp, age and a lot of other non-essential parameters.

By building the leds into a bar that mounts just below the water line along the front of the tank, illumination of plants and fish will be easy to control, and many irridescent fish will light up unbelievably. Note that the directional design of the LEDs means no reflector is probably needed or desired. A diffuser in front of the LEDs can be used if more spread is needed, but it will cost efficiency, fiercely, I suspect.

Narrow-beam LEDs are made worse when the beam hits the water, as all rays are bent toward the center of the beam, somewhat. The surface acts a little like a focussing lens. Immersed, they will actually probably spread much wider as the index difference between lens and water is much less than the lens-air difference. Surface refraction and reflection are no longer the problem they are with hoods in air, and the illumination may be really efficient. Heat can be conducted away from the LEDs by a simple aluminum heat sink that extends up out of the water, if that is needed.

LEDs typically operate at only a few volts, so the insulation needed is just a thin paint of silicone potting compound o/e. [I would still provide a good ground on the assembly just in case something fails in the power source. That and a GFI could save your fish, or your life, even! :-)]


-- Wright Huntley -- 760 872-3995 -- Rt. 001 Box K36, Bishop CA 93514

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