On Wed, 19 Dec 2018 20:30:37 -0000, trader_4 wrote:

On Wednesday, December 19, 2018 at 2:36:55 PM UTC-5, William Gothberg wrote:
On Wed, 19 Dec 2018 17:47:17 -0000, trader_4 wrote:

On Wednesday, December 19, 2018 at 11:35:06 AM UTC-5, William Gothberg wrote:
On Wed, 19 Dec 2018 16:21:41 -0000, Mark Lloyd wrote:

On 12/19/18 6:01 AM, William Gothberg wrote:

[snip]

They probably are fairly crude. I know they flicker, for example if I
use my cordless drill, the chuck appears to spin the wrong way under the
LED lighting.
I remember seeing that with a washing machine (under fluorescent
lights). As the tub was slowing down, the row of holes around the tub
would appear to reverse direction. Same thing with (spoked) wagon wheels
in movies.

It looks absolutely ridiculous with modern cars with LED headlights in films. How hard can it be to put a smoothing capacitor on the output of the power supply?

I've never noticed that. Any films come to mind?

A lot of Top Gear programs showing the DRLs of cars fitted with LEDs. With a feature film, they might take the time/trouble/money to do something to stop it.

It seems especially
weird, since cars have a 12V supply with a big battery to smooth
anything out. I guess the power supply that reduces that to whatever
the LED headlights use though might have a switching power supply these
days too.

AFAIK it's deliberate, making the LEDs operate brighter than they are capable of, but only 1/4 of the time. Our eyes just see the brightest part of the cycle, so we think they're four times brighter than the LED is really capable of, without overheating itself.

If that's the case, then many similar LEDs, eg house bulbs should be designed
the same way.

You'd think so.

Which means the pulsing is designed in, deliberate and
has nothing to do with the type of power supply or that the power comes from AC.
First time I've heard of this, but it's certainly possible.

The one's I've got I believe are not pulsed on purpose. I say this because one of them failed - it started flashing at about 3Hz. I fixed it by just putting a fairly large smoothing electrolytic capacitor on the output of the 70V DC PSU. It now operates (and has for a year) at the same brightness as the others without breaking the LEDs. And it's lovely and smooth - no high frequency flicker! If the others annoyed me enough, I'd take them all apart and fit capacitors. As it is I only actually notice the flicker if I move my line of vision rapidly across them, or I'm using something like a drill that's moving, and it appears to rotate the wrong way. But some car lights flicker slow enough that you see them, and also your eyes are moving about when driving anyway so you're more likely to see it.