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Comment by libria | Hacker News Reader

If the LED driver handles dimming through PWM, no thanks. The flicker is very noticeable. Also, the 20k hour figure for LED's doesn't factor in "lumen maintenance": LED's can dim with use, especially high output use or possibly poor ventilation. Lumens after 10k hours may not be the same as new. Last, it's hard to find a good warm (2700k?) LED that is remotely efficient, though the Cree XP-G's seem to be getting there.

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The dimming is generally done on the AC side before it even reaches the bulb. So it would be dimmed by either resistive (unlikely) or by cutting the AC waveform by timing the zero crossing point.

For more information, and a look at the waveform that is produced see this awesome page: http://www.epanorama.net/documents/lights/lightdimmer.html

You are right about the PWM dimming - but it's a better alternative to the lack of dimming of CFL bulbs.

The 20k hour figure likely does figure in "lumen maintenance" - although Switch maybe stating a "consumer lifetime", the mean lifetime of the product, they are required to provide a lumen maintenance figure called L70 - the time it takes for a 30% reduction in light output. Chances are these light bulbs just broke before reaching that target, and the consumer lifetime is more useful to the market at large.

And, yes, the warm color with high CRI is the hardest LED to make - that's why they're waiting until next year to try and offer a warm white 100W equivalent bulb.

If you notice flicker, the PWM frequency is too low. I recently built a PWM driver for high power RGB LEDs and there's no flicker, even at very dim brightness. I don't know what's on the market, but probably I should get into it ;)

You wouldn't even notice any flickering at a PWM frequency of 120 Hz. Linear (resistive) dimming is just not done anymore. Just about all lighting fixtures these days dim by either PWM or chopping the AC signal.

"If the LED driver handles dimming through PWM, no thanks. The flicker is very noticeable."

The flicker is unnoticeable if the chop rate is a few kilohertz or higher.

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