Ernest Christley wrote in message news:YE47c.1569

BTW, all LED's can be 'overclocked' by pulsing them at a high freqency.
The current rating is limited by the heat it produces. The light is a
function of the voltage. Pulse the light and get more light, but don't
leave it on long enough to burn the LED.

While it is true that you can pulse current to LEDs to achieve a
higher peak output, this does not make it appear brighter to your eye.
The human eye integrates the light output as a time average, so an
LED that pulses at twice the current for 1/2 half the time will look
no brighter than one that is running steady state. In fact, it may
actually be dimmer because LED efficiency can drop at higher currents
due to current saturation of the junction hole/electron pair
generation/recombination function. There is a range of operation at
around 5Hz where pulsed light can appear brighter than steady state,
but this frequency range is too low to be useful because of the
visible flickering of the light. This is due to the psychophysical
characteristics of the human visual system.

Also, the total power dissipated by the LED package is a function of
the average current. Pulsing at twice the current for half the time
dissipates the same power as steady state operation. Proper heat
sinking of the device is important to maintain quantum efficiency
which is highest at cold temperatures and drops as the device heats
up.

PWM of LEDs is really only useful for dimming. At full on, it
operates steady state, and to dim it you start chopping the current
for longer and longer periods of time at the PWM frequency to dim the
device.

Dean Wilkinson
B.S.E.E.
Former Boeing 777 AIMS Display System engineer