Like most postings, it draws varying opinions, but gets you thinking. At the
risk of asking a dumb question, you refer to "white LED Lamps (not LED's)
are a different beast." What do you mean by LED Lamps. If they are a
different beast, what are they?


"Meindert Sprang" wrote in message
...
"Terry Spragg" wrote in message
...

Sorry Terry, but your post contains a lot of mis-information.

The cheapest source for white LEDs at present seems to be salvage
from solar yard lights on sale.

OEMs are buying them all up in bulk, I guess, I have not yet seen
any at radio shack, or even my parts wholesaler catalogues.

White LEDs are commonly available at all major wholesalers.

Each LED consumes about 80 milliamps at 1.6 volts or so.

No. The voltage drop across a LED depends on the color of the LED.
Red LED's drop 1.6V, green and yellow drop appr. 2.0V and blue and white
LED's drop around 3.5V.

But the voltage is not what you apply. You apply a current, which is 30mA
maximum for normal LED's. So, add up all voltages of all leds you have in
the string, subtract it from 13V, devide the remaining voltage drop by
0.03
et voila: your resistor value.

The white LED Lamps (not LED's) are a different beast. These draw a higher
current and are mostly fitted with a current limiting resistor. Never
assume
a working voltage of these types, always check the datasheet of a specific
type.

be strung in series so that 5 would require 8.1 volts or so to
ignite, and require a specific resistor in series in the range of a
couple hundreds of ohms to protect the devices from overcurrent, as
they cannot protect themselves or control current in the way we
usually think with ohm's law, as they have conductive
characteristics quite different from resistors, incandescent or
otherwise. More like a gas discharge tube, really.

They're just a diode and like all diodes, they will blow if you connect
them
directly to a voltage source higher than their junction voltage.

Reverse
connection means they just don't conduct or light up unless exposed
to excessive voltage, in which case they melt and fuse to become an
open circuit.

LED's have a very low reverse breakdown voltage of around 5V.

They can be driven from an A.C. source, conducting
like rectifiers.

No, because of the low breakdown voltage. You can either connect two
anti-parallel or of you need only one LED on AC, add a normal diode
anti-parallel to conduct during the negative halve of the AC cycle. This
way
each diode or LED limits the other's reverse voltage to it's own junction
voltage.

Yes, they are much more efficient than regular lamps, consuming
about 1/10 the power for equivalent light output, but, at the
present state of the art, high intensity leds are not really very
bright.

Have you ever stared into a LumiLED without wearing shades...?

Meindert