flickering headlights - new technology?

[Killed_by_Death]

Today on the way back from GC & SA I passed a vehicle & then flipped on my signal to change lanes.
I've got a lane-watcher camera in my passenger's side mirror & it looked like the vehicle I'd just passed was flashing their lights at me at a very fast rate.

I looked over my shoulder & their lights were steady.
So, my conclusion is that the headlights in that vehicle are on a oscillating power source, probably to save power.

The frequency of the strobe coincides with the frame rate of my camera.

You'd think that a oscillation like that would actually use more power, but...

 

[megafiddle]

Had to look it up, but it seems there are LED headlights now. Very likely what those were.

Strobing the power with an incandescent headlamp would not produce any noticable flicker. The massive low voltage filaments cool far too slowly.

-

 

[Alkali Ike]

Pulse Width Modulation or PWM. Basically they're powered by an ON/OFF/ON square wave, not solid DC ON. Reduces power consumption and extends LED life.

Invalid Link Removed

 

[Killed_by_Death]

Makes sense that it would use less power on LEDs. Mine are Halogen, so a modulated pulse would probably actually consume more energy to re-ignite the gas over & over.

 

[Alkali Ike]

I admit I had to look it up. I should post in the "What did you learn today" thread. Ha.

 

[Killed_by_Death]

Hadn't heard the term Pulse-Width Modulation since 1999 on a Y2K project.
Some of our data transmission was done over modems with PWM, basically ones & zeros transmitted in a stream of ups & down (square waves).

Maybe all modems do, since modem = modulate - demodulate.

 

[D M C]

Don't discount the possibility that you were having a stroke.

 

[megafiddle]

Makes sense that it would use less power on LEDs. Mine are Halogen, so a modulated pulse would probably actually consume more energy to re-ignite the gas over & over.

The halogen gas doesn't ignite (or glow) . Its purpose is to allow higher filament temperature. Halogen lamps are still incadescent lamps; they just run at a higher and more efficient color temperature (more blue).

If you tried to lower the power supplied to an incadescent lamp by pulsing it rapidly, the heating effect, and therefore the light output, would decrease to the RMS level of the pulsed power. This is basically how light dimmers work. The filament cannot heat and cool rapidly enough to keep up with the power pulsations. So it effectively smooths out the pulsations and produces a lower power light output.

An LED produces full light output during the "on" portion of the power pulse. The very short dark intervals are filled in by our persistance of vision. So even though the average light output is less when an LED is pulsed, we only see the full peak output. The level of brightness of a pulsed LED is an illusion.

-

 

[Killed_by_Death]

Yeah, our eyes are slow.
I can remember seeing this phenomenon as far back as the first consumer videocameras.

If you pointed one at a television that was on it looked all funky, because of the frame rates & the way the raster drew the picture on the tube.

 

[Alkali Ike]

Not to drift off topic but this reminds me of why movies standardized on the 24 FPS frame rate. It's a combination of factors but basically it boils down to 24 FPS being the slowest they could go (thus conserving film) and still maintain a reasonable perception of live action. We've all become so conditioned to 24 FPS that we ignore or just don't notice the artifacts. Peter Jackson tried 60 FPS HFR High Frame Rate in his LOTR movies and it looked unnatural and distracting to most viewers (including me).

Anyway, you combine the slowest practical flash rate with persistence of human vision, and you don't notice the flicker.

 

[megafiddle]

Not to drift off topic but this reminds me of why movies standardized on the 24 FPS frame rate. It's a combination of factors but basically it boils down to 24 FPS being the slowest they could go (thus conserving film) and still maintain a reasonable perception of live action. We've all become so conditioned to 24 FPS that we ignore or just don't notice the artifacts. Peter Jackson tried 60 FPS HFR High Frame Rate in his LOTR movies and it looked unnatural and distracting to most viewers (including me).

Anyway, you combine the slowest practical flash rate with persistence of human vision, and you don't notice the flicker.

If I'm not mistaken, 24 FPS movies have a flash rate of 48 per second; every frame is flashed twice.

The rate requirements for smooth motion are lower than those for a flicker free view. Even still frames with no motion at all require 48 per second flash rate to seem flicker free.

It's interesting how they convert 24 FPS film to 30 FPS NTSC video. Every 4th frame shown twice; the frame sequence is 1,2,3,4,4,5,6,7,8,8, etc.

-

 

[Stewie26]

The original old time movies were shot at 16 to 18 frames per second. Hence, that is why the word, "Flicks" originated when referring to movies.

 

[Diamond_Dave]

Don't discount the possibility that you were having a stroke.

Occam's razor.

 

[Stewie26]

Not to drift off topic but this reminds me of why movies standardized on the 24 FPS frame rate. It's a combination of factors but basically it boils down to 24 FPS being the slowest they could go (thus conserving film) and still maintain a reasonable perception of live action. We've all become so conditioned to 24 FPS that we ignore or just don't notice the artifacts. Peter Jackson tried 60 FPS HFR High Frame Rate in his LOTR movies and it looked unnatural and distracting to most viewers (including me).

Anyway, you combine the slowest practical flash rate with persistence of human vision, and you don't notice the flicker.

Back in the 80's, Douglas Trumbull patented a 60 frame per minute immersive film process utilizing 70mm film called Showscan. Trumbull also produced the special visual effects for 2001, Close Encounters, Star Trek, Blade Runner, BrainStrorm to name a few and loved to tinker with new film and visual effects ideas. The images looked amazing real but the downside is it consumes 2.5 times the amount of 70mm film which was/is very expensive to shoot in. When you watch films shot at 24 FPS, you will notice a spinning wagon will look like it is revolving backwards. At 60 frames, this artifact is corrected and the wheel spins forward. Anyway...sorry if that is TMI. It's just that I made my living doing this stuff for the past 35 years.
Showscan - Wikipedia
Invalid Link Removed

 

[Alkali Ike]

Yeah, 80 years or so ago someone figured out (correctly) they could get away with 24 FPS and it would look real enough.

I've never been able to understand how 3:2 pulldown works for converting 24 FPS to 30 FPS. I understand what they're doing but I don't understand why it works.

Just to get back on topic, what's the frame rate or frequency of these new PWM headlights? Ha.

 

[two fingers]

Pulse Width Modulation or PWM. Basically they're powered by an ON/OFF/ON square wave, not solid DC ON. Reduces power consumption and extends LED life.

Invalid Link Removed

Beat me to it.

It's why the strobing gets even worse when you use dimmable LED lamps. Dimming is accomplished by increasing the amount of time between pulses. Wave something in front of your face when dimmable LED are on about half bright. It's crazy looking.

 

[Jeff Scott]

Not to drift off topic but this reminds me of why movies standardized on the 24 FPS frame rate. It's a combination of factors but basically it boils down to 24 FPS being the slowest they could go (thus conserving film) and still maintain a reasonable perception of live action. We've all become so conditioned to 24 FPS that we ignore or just don't notice the artifacts. Peter Jackson tried 60 FPS HFR High Frame Rate in his LOTR movies and it looked unnatural and distracting to most viewers (including me).

Anyway, you combine the slowest practical flash rate with persistence of human vision, and you don't notice the flicker.

Back in the 80's, Douglas Trumbull patented a 60 frame per minute immersive film process utilizing 70mm film called Showscan. Trumbull also produced the special visual effects for 2001, Close Encounters, Star Trek, Blade Runner, BrainStrorm to name a few and loved to tinker with new film and visual effects ideas. The images looked amazing real but the downside is it consumes 2.5 times the amount of 70mm film which was/is very expensive to shoot in. When you watch films shot at 24 FPS, you will notice a spinning wagon will look like it is revolving backwards. At 60 frames, this artifact is corrected and the wheel spins forward. Anyway...sorry if that is TMI. It's just that I made my living doing this stuff for the past 35 years.
Showscan - Wikipedia
Invalid Link Removed

Stewie, have you seen any Showscan films?

A friend of mine introduced us to Doug at an NAB Show in the late mid '1980s. He invited us to a demo showing of his latest (at the time) technology (Showscan) at his office in Marina Del Ray where he had a small theater decked out with the Showscan system which included a really nice sound system (including subs under the arena seating area). It was a truly awesome experience; also, the way he formatted the demo was brilliant.

 

[Stewie26]

Stewie, have you seen any Showscan films?
A friend of mine introduced us to Doug at an NAB Show in the late mid '1980s. He invited us to a demo showing of his latest (at the time) technology (Showscan) at his office in Marina Del Ray where he had a small theater decked out with the Showscan system which included a really nice sound system (including subs under the arena seating area). It was a truly awesome experience; also, the way he formatted the demo was brilliant.

Many times more than I could count. Definitely, the best image fidelity I have ever witnessed. I got the honor to work with him on dozens of Showcan projects. He dropped by my office just few months back in late 2017 working on a new project. It was really good to see him again. Doug is 75 now and still going strong and still inventing things.
Sorry to "Killed by Death" for getting off track on your thread here. Carry on.

 

[Jeff Scott]

You look just like the dog in your avatar. So it is you driving the boat!

 

[Killed_by_Death]

Sorry to "Killed by Death" for getting off track on your thread here.

Not at all. That was the point of the thread, just a conversation starter.
It's a shame that cost is always the bottom line in making decisions, or we might be seeing films in ShowScan at our cinemas.