Hi there,
Gee that thread ended up being pretty long :-)
The bottom line is, LEDs are current driven devices
not voltage driven devices so a current regulator is
the best way to drive one.
The problem with a voltage regulator is that the voltage
across the LED varies with current for a number of
conditions, including the manufacturing process and
operating temperature. This means with a voltage
regulator the brightness of the light will vary from
LED to LED and possibly as the light gets warmer too.
With current regulation the LED always gets the
correct current, so you can assume it is always driven
correctly.
As a final analysis, the brightness of an LED will vary
somewhat with temperature even with a constant current,
but trying to compensate for this with a voltage regulator
type circuit isnt the right approach. Measuring the
forward voltage might be nice, but it would complicate the
circuit too.
Take care,
Al
