On Sun, 28 Dec 2008 11:24:43 +0100, "Steve Lusardi"
wrote:

None of the responders have addressed the concern I raised, life span. Larry
is correct, in order to dim the light output of LEDs, you limit the duty
cycle, not the current. Yes Bruce, resisters limit the LED current, but to
what level? The greater the current, the brighter the output, but the cost
of this is durability. The brighter the burn, the shorter the life. What is
the correct device current? Normally it is whatever the LED draws .2V more
than on voltage, which differs depending on the LED color. Anything more
than that affects device life. It is that voltage you should regulate to for
maximum life. It is not to the manufacturer's advantage to tell you that.
They are perfectly happy to sell you replacements. This rule is also valid
for Halogen lamps. Voltage regulators are prudent, but not required, just
understand the trade off in longevity.
Steve

Every document and specification I have read related to LED output or
life states that current is the limiting factor and data is freely
available concerning output, current, life, etc. Plus there are
innumerable circuits available for LED circuits.

Using a pulse rate or width supply is just a simple, cheap, and easy
method of controlling the total current through the LED.

The point with the LED "tubes" is that they are designed to be used in
auto circuits (I believe) and they are built to survive in that
service. Initially I did install regulators for each light but found
that the tubes were already current limited to the point that adding
any resistance at all to the circuit caused the lights to dim
noticeably and certainly having them on with 14.1 VDC system voltage
hasn't bothered them yet.

I really don't know how long these lights will last and to a great
extent I don't care. The individual LED's can easily be changed so
other then minor inconvenience a burned out LED isn't really a
problem.
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)