Please note the interpolations:

On Wednesday, October 31, 2018 at 11:33:32 AM UTC-4, Terry Schwartz wrote:
Oh those troublesome holes. Takes forever to fill 'em. Insatiable.

LED's are much faster than incandescents. Look at most any vehicle that has LED's in the side mirrors and incandescents in the rear turns. The timing is visibly different and painfully obvious. At least one vehicle maker has recognized this and compensated for it in the driver timing, even PWMing the LEDs during turn on to emulate the familiar incandescent "warm up".

There are LED lamps and there are LED lamps. "Responsible" makers such as RAB & Cree (and a few others) feed smoothed DC to their lamps, greatly reducing and/or eliminating flicker. Some few of the retro-lamp makers (those that require removal of the ballast and so forth) do the same. But far fewer than with the complete fixture.

The inherent flicker in LED tail lights (and other LED lighting) bothers the crap out of me. I know not everyone sees it, but apparently my eyesight is a bit more responsive than some. I see the flicker in neon signs and various LED backlights as well.

Agreed on this. But, as you note, some makers take care to handle this in their vehicles. Our Ford C-Max side-mirror led signals are synched well for example. Vehicle systems can be a mixed bag, depending on how well filtered the Alternator might be.

The PWM rate is designed to be faster than normal visual threshold of detection, but below the audio threshold of annoyance... that is, over a hundred HZ or so, but out of the sweet spot of human hearing, a few hundred HZ to a few KHz. It seems counter-intuitive that the visual threshold is lower than audio, but in this case, it is.

The PWM rate could easily be set above the hearing range, but that has potential implications for causing EMI certification problems.

We installed LED lights in our bathroom fixtures -- and one of the wifes' hair appliances modulates the LED bulbs badly. I'm not sure if I should blame the bulbs or the curling iron in this case.

See the first instance. We tried (cheap, as in FREE) some utility-supplied LED lamps in the kitchen at our summer house - and instantly lost FM reception anywhere within a 30' sphere of these lamps. We switched over to SMT LED fixtures (no separate lamps) and all became well.

I will soon find out a lot more about LED retrofits. We are about to install about $1,500,000 in conversion fixtures and retro-lamps in the buildings I manage based on a fairly chunky Utility rebate. These are medical offices, outpatient clinical spaces and heavy-duty research facilities - gene splicers and all that. So, if there is any tendency for mutual interference, I will know soon. The installer says not. Famous last words, or not.

It is a very mixed bag, and one size does not fit all.

Terry

All LEDs have some start delay. Even the original ones used for
indicators had a short delay. It's while the electrons fill the
electron holes where they should be.

Steve

--
http://www.npsnn.com

Peter Wieck
Melrose Park, PA