Re: LED Xmas lights

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?

>> You should see the drop across 2 diodes, 1.4V. Also, are you sure you
>> switched the meter from AC to DC?
>
>Soitenly. Putting it on DC gives an even more ridiculous number.
>

Oscilloscope?

>If enough LED's would be connected in series could they dispense with the
>resistors entirely?

Supposedly you can't, since a LED in breakdown (necessary for it to
light, voltage needs to be at least 1.5V or higher for blue LEDs) has
a very low resistance, and would draw too much current without a
resistor. I have seen LEDs used without resistors on small batteries,
with high internal resistance.

Resistors do dissipate some power (reducing energy efficiency of the
lighting system). Maybe someone could figure out a way around this
someday. Maybe a duty-cycle controller like that used in incandescent
light dimmers.

BTW, I did once (accidentally) connect a LED to 12V with no resistor.
There was a POP and half the LED package disappeared (moved too fast
to be seen, like a flea jumping). The remaining half (attached to the
leads) did look burned around the chip.

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.
--
23 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin
.

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