The Natural Philosopher wrote:


I think about 4 for a blue white. There is a relationship between that
and the frequency emitted. Quantum crap or summat.

If you plot Vf versus center wavelength, the slope
of the line allows derivation of Plancks constant.

(Done for some fool physics lab experiment, with
some crusty old spectrometer to check the LEDs.
You could still see Plancks fingerprints on the
instrument.)

They even have a picture of Mr.Plank here. And you
have to plot Va, not Vf. Drat!

https://www.scienceinschool.org/2014/issue28/planck

*******

The LEDs on my bicycle light (blue with white phosphor)
have a Vf of 2.5V at 11mA. The voltage (being
a diode curve) rises a bit when you start pumping
an amp through the high-power LEDs. I might have a commercial
datasheet or two listing 3.2V or so at ampere level.
The highest current value I've ever seen anyone
put through a single LED was 17 amps. No idea
what the voltage is then :-) The LED in that case,
was soldered onto a solid copper block, and relied
on thermal inertia to protect the LED during a
short (blinding) experiment.

LEDs are not very efficient when you do that.
You don't get 17x the light when running
17 amps versus 1 amp.

This is one reason the bicycle runs LED arrays and
not single LEDs. The LED arrays make better
use of the limited power (3W on a good day).
Due to the Vf being a bit low, the design only
uses 2.5W of the available power. If I could
get a 3V LED at 11mA, I'd be using it, as then
I could set the operating point at 6V (two LEDs
stacked, which is how it always runs). Running
6V @ 500mA would use the available 3W of generator
power. Running 5V @ 500mA (with all the LEDs
running in parallel in pairs), draws 2.5W.

I was a bit disappointed to see they were running
at 2.5V.

Paul