On 6/4/2016 8:01 AM, HerHusband wrote:
The LED itself regulates voltage. That's what a diode does.

http://www.merriam-webster.com/dictionary/diode
an electronic device that allows an electric current to flow in
one direction only

It has been many years since my electronics days, but I believe a diode
does have a fixed voltage drop. I think it's around .7 volts if I remember
correctly. So it does regulate the voltage in some respects.

A "regular" silicon diode has *about* a 0.7V forward drop. Though the
actual drop is dependant on the current flowing through the junction (as
current increases, the drop increases -- but only slightly; not
proportionately as with a purely resistive device). There's a "knee"
in the V-I curve at that point (but, all knees are "rounded" to some
extent!)

LED's, OTOH, have a much higher forward drop. Some of the high efficiency
ones are as LOW at ~1.7-1.9V. Most, however, tend to be higher -- ~2.1
for Red/Yellow/Orange and closer to 3.4 for the Blue/White devices.

(Even these are just ballpark numbers as it depends on the dopants used)

Germanium ("Is there life on Germanium?") diodes have forward drops in the 0.2V
range. Schottky diodes are in the 0.15-0.45V range.

And, of course, you can get zeners at all sorts of voltage ranges (but, these
are operating in reverse bias when zenering)