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Comment by Tepix | Hacker News Reader

Regarding flicker: Use the slow-mo video function of your smartphone camera to check for it.

Some cameras have slow-mo modes which try to remove lighting flicker by having a special high sample rate light sensor whose purpose is picking up the flicker and then using software to compensate the rest of the image data for the flicker pattern, using as input the time the shutter opened and closed for each row of pixels of a video frame, and integrating the light sensor value over this time.

This; state-of-the-art mobile cams should be "beating" the flicker, even in slo-mo. I'd wager the latest iphones can, although I don't have one to test.

A lot of places use fluorescent lights which will look real weird if caught in the frame without some kind of flicker compensation just as one example so its pretty important.

Uncited rumour is iPhones for the last ~3 years have had special flashlight LED's (made by NXP?) which also embed an RGB colour sensor for exactly this reason. The LED's when reverse biased send out the results of the RGB sensor. It has been suggested the reason they didn't use an extra pin was to hide this anti-flicker feature from competitors who were sure to do a detailed teardown of the phone.

There are x-rays of the LED here: https://www.chipworks.com/about-chipworks/overview/blog/true...

Or just look at your finger while you wiggle it vigorously.

What would you see with, and what without flicker? I can wiggle my finger vigorously, but now I still don't know whether my LEDs flicker...

You'll see extra discrete instances of your finger, as though lit by a strobe light.

This is how we used to be able to measure speed of spinning objects too. :)

Maybe not, but if you do it hard enough while listening to some terrible music, you'll have replicated my 90s clubbing experience.

With a continuous (non-flickering) light you see your blurred finger. With a flickering light, you'll see your blurred finger with gaps in the blurring. This effect is especially pronounced with sharp-flickering light (like in LEDs) as opposed to gradually-flickering light (as in incandescent bulbs). CCFLs are somewhere in the middle.

I did this during my quest to find a flicker-free LED light bulb. I found that basically all of them flicker. Some appear to alternate between banks of LEDs to reduce the dynamic range(?) of the flickering, but they all flicker. Home Depot has a rack of LED bulbs that are always turned on, so that's a good place to test many models at once.

My first thought was: why don't they just filter the output? My guess is that perhaps LEDs are more efficient when being driven full ON or OFF rather than with a steady DC.

> My first thought was: why don't they just filter the output? My guess is that perhaps LEDs are more efficient when being driven full ON or OFF rather than with a steady DC.

It's actually the opposite, efficiency goes down when current goes up.

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