Re: [APD] LED Lighting

["S. Hieber" <shieber at yahoo_com>]

he he  The bulbs don't mind being emersed sub the leads on
them tend to be fussy. All Electrically conductive parts
must be insulated and waterproofed before bringing near
water.

I know that Wright is well aware of this, but at the
mention of putting LEDs in water, I thought it deserved
mentioning.



As for control. Specs are usually given for voltage ranges
-- control the ammps or the voltage but either way, don't
overjuice them (tech term) or they'll say bye bye quickly. 

Wright do you really think transistors are needed in a
power supply? Low voltage DC, a rectifier and some
resistors ought to do the job. But with enough to light a
tank, even the resistors would be redundant, no?

Scott H.

--- Wright Huntley <whuntley at verizon_net> wrote:
> 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! :-)]


=====
S. Hieber

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