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Re: [APD] LED Lighting

Message: 6
Date: Mon, 29 Dec 2003 13:14:57 -0800 (PST)
From: "S. Hieber" <shieber at yahoo_com>
Subject: Re: [APD] LED Lighting
To: aquatic plants digest <aquatic-plants at actwin_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

Of course, but the voltage per LED is so low the leakage current would be trivial, I suspect, unless the tds was really way up there. It certainly isn't up with the CF lamps I was immersing a couple of years ago. Those carried some truly lethal Voltages/currents and the current in water would have been more than non-trivial!

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

As I said, a simple painting of all contacts with silicone potting compound would be enough to do the job for the next couple of decades or more. :-) Short term, the soft vinyl paint sold for painting pliers handles probably would work, OK.

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.

Very true, but Voltage specs are too loose to provide even the slightest protection. Use them for deciding how many a given power supply will drive in series (with a bit left for regulation/overhead) but design the control as a pure current source.

The most badly-speced devices known are optoelectronic components. They will have a somewhat typical Voltage drop, but the power expended and the power out are virtually entirely determined by the current flow.

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?

The high impedance of a transistor collector is probably cheaper than all the stuff you have suggested. :-) Don't forget that transistors are often way cheaper than resistors, these days, unless you want individually packaged ones. :-) Resistors can act as current sources, but must waste a lot of power to do so, and I find extra heat a problem with most lamps. A 5V wall wart with a simple transistor array driving arrays of several LEDs in series is a pretty cheap "ballast" as such things go. Yes it needs at least one or two resistors, but they need not be conducting all that current and creating heat.

My ideas may be a bit overdone, but I would like to roughly regulate the current to maintain constant output with age, temp, etc. Wouldn't that be kind of nice? Cheap, too, I suspect, compared to the cost of the LEDs. Traffic lights have made red and green into cheap commodities, but good blue is still a big problem, both in cost and maybe lifetime. Cheap 10,000 K may still be a way off. ;-)

I see more problems working out mountings and attractive housing. How do we keep food from fouling them, etc.? Will algae quickly grow on the plastic lens and turn them off?

Gotta go chop some wood. Came home from So.CA to frozen-up water lines, last night. Finally cleared by this afternoon, but the snow level is down about 100' above the valley floor and dropping. Come to think of it, I'd like some lights that put out a *lot* of heat, right now. :-)


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

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