Re: LED Xmas lights

In article <7qv0p1t5b3kq396ls59so20i8fnrgtqtb3@xxxxxxx>, Mark Lloyd wrote:
>On Fri, 02 Dec 2005 05:10:00 GMT, Steve Kraus
><screen@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>Mark Lloyd wrote:
>>> Does adding the capacitor make any difference (that is, if you have a
>>> large capacitor that'll work on 180V or so)?
>>
>>Haven't tried that yet.
>>
>
>Would a capacitance of 220uF be OK for this?

Current inrush when you plug this thing in could cause nasty sparking
where contact is made and may be hard on the rectifier unless it's rated
a good 3-4 amps or more. I would add a power resistor of a few ohms in
series with the AC line. I would also add a fuse in case a voltage
transient breaks down the rectifier or the capacitor fails.

>Another thing, I learned about LEDs in college. The semiconductor
>material used determines the color. There were no blue LEDs at that
>time (blue is at the high end of the visible spectrum). There are blue
>ones now. However, I still don't understand WHITE LEDs (there is no
>single frequency for white, like for the other colors). White could be
>made from red, green, and blue but I see no evidence of them in a
>white LED.

The usual white LEDs have a blue LED chip coated with a phosphor that
absorbs some of the blue light and fluoresces yellow light. The phosphor
output is a fairly broad band from mid-green to mid-red in the spectrum,
so white LEDs are not really horrible with color rendering.

- Don Klipstein (don@xxxxxxxxx)
.

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