Inferior how? Yes the colour does change with varying current, but it's
rather strange to suggest it's optimised at full current - that's simply the
point it is specced at. You can in fact typically get a different binned LED
which will have the same colour at 350mA as your original one does at 700mA.
In any case, the effect is actually pretty minimal and something you can
pretty much ignore unless you're using the LEDs to illuminate artwork. The
other question of course is what exactly is "full current", given you often
get specs for more than one drive current.

Even more bizarre is your mention of brightness per mA varying with
different drive currents and this being optimised at full drive current. In
fact LED efficiency (since this is what you're referring to) improves with
decreasing drive currents, so by "optimised" you can only possibly mean
"minimised" :-)

On 6/7/07, Russell McMahon <apptech@paradise.net.nz> wrote:
>
> > I am controlling a number of Luxeon LED with PWM using PIC12F family
> > capabilities.
> >
> > I've been using a simple LM317 constant current configuration and
> > now wanted
> > to move to a DC-DC circuit to reduce power loss.
>
> Whatever arrangement you use should always run the Luxeon at full
> current when it is running, with the duty cycle altering to control
> brightness. This is because the LED colour and brightness per mA vary
> as current varies and they are optimised and specified at full
> current.
>
> If you use PWM to produce a lower than rated current on average, and
> then filter this so that the LED sees DC, rather than seeing PWM at
> full current / no current then you get inferior results.
>
>
>
>         Russell
>
>
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