Re: Power & reliability issues for UV leds


"distar97" <distar97@xxxxxxxxx> wrote in message
news:1135271535.758395.138930@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>I recently got an inexpensive HK keychain light with a UV led. It
> worked great at first. After a very short amount of time, the
> brightness dimmed to a useless level.
>
> Thinking it had cheap 2016 (2) cells to begin with, I replaced them. No
> effect. Then I noticed there is no current resistor or even space for
> one. The led leads are simply placed above and below the 2 cell stack,
> finger pressure makes the contact. So the 2 cells (6Volts) go directly
> to the led leads. Does this sound right? Not to me.
>

Most of the cheap keyfob LED lights are like that. They are designed with
the idea that the internal resistance of the batteries is sufficient to
limit the current, and that although the LED is overdriven very hard, it
should last the couple of hours the batteries last. Also, they generally
have a momentary switch which may extend their life a bit as the LED is
unlikely to be powered for more than a few seconds at a time..

> I remember reading about reliability problems with UV leds. Is that
> still the case?
>

Don't know, but my blue keyfob drew 60mA, and taking the resistance of my
AVO into account, it was probably much higher than that. No standard LED is
going to survive that sort of abuse for long.

Dave


.

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