Driver efficiency?

how_crazy_is_this · October 7, 2011, 1:45pm

I have read on this site that current regulated drivers are more efficient than PWM. I have read other info that suggests that PWM may be a more efficient way to regulate current.

Is there a definitive answer to this or are there too many factors that can result in either being more efficient in a given application?

I ask this because it is my understanding that an XM-L is about 20% more efficient than an XP-G. However, when I tested a Xeno EO3 XM-L against my TrustFire R5-A3, the R5 had about 2X the run time at what appeared to my eye to be about the same amount of light output. (Both lights at their lowest setting.)

I could notice more light output on the highest setting from the XM-L (didn't do runtime tests on high). However IIRC, on low the output, the 2 were very close. Think I would have noticed if the R5 were less that 1/2 as bright.

Fortunately my eyes are not sensitive to PWM. I think the PWM in the R5 must make it more efficient. Why else would a less efficient LED appear to put out about the same amount of light for 2X as long as a light with a more efficient LED?

Thanks,

Wade

HKJ · October 7, 2011, 3:12pm

PWM has nearly always the lowest efficiency, this is because the electronic and led is running at high current when on. All resistive losses in the driver is higher at high current and leds has a lower efficiency at high current.

A direct drive or current regulated led with pwm regulation might have better efficiency at full power (i.e. pwm is not used), than anything with buck or boost regulator (This will depend on a lot of parameters).

agedbriar · October 7, 2011, 11:37pm

I believe it's pretty much hopeless to try and visually compare total lumen output between two lights with different beam profiles. The floodier light directs many lumens into the spill, where they don't create that much visual effect.

One reason for the latter is the wide area that the spill covers compared to the hotspot. Another might be the fact that part of the spill falls in the peripheral vision range, which our brain doesn't register so well.