LED Efficiency vs Drive Waveform

[**DONOTDELETE**]

I am interested in finding out whether there is an efficiency peak when operating LED's from a switching power supply (constant current supply). Do led's prefer a straight DC drive for maximum efficiency? Does efficiency change with drive frequency and/or waveform applied? Many of the newer chip IC's that are built for this application can obviously run a your frequency of choice. My guess is that using the highest frequency possible will reduce component size, (especially circuits employing an inductor), while keeping in mind that you don't want to start losing power by radiating RF. Perhaps I should address this question to the scientists at Agilent that are working on this technology?
Thanks,
WhiteFox

 

[dat2zip]

WhiteFox,

LEDs prefer constant current as the prefered method of regulation. DC current is the most efficient of all means that I'm aware of.

Pulsing LEDs are not as efficient as straight DC current. Pulsing LEDs will effectively reduce the overall brightness. A 50% duty cycle at any frequency will appear to the human eye as 50% bright since the eye integrates the light output.

If you want to preserve the CCT value of white LEDs, then PWM them to vary the brightness. The on state should be set for the rated LED current (~20mA for 5mm, 350mA for 1W Luxeons...).

LEDs like any other diode have turn on and turn off time that may not be specified.

Wayne