What causes these video artifacts?

[Paul Schmehl]

This is a video taken today. At around the 40 second mark I drive up behind a Tesla. Look at the Tesla's lights. His right turn signal is on, but it's flickering. I've noticed this flickering in traffic lights as well. If you look at the red lights, they're flickering. What causes this?

 

[kamkar]

Thats the manifestation of the difference between the refresh rate of the light ( mains lights in US 60 HZ i think and 50 over here in EU ville )

You will also notice that LED lighting on many new cars also seem to flicker.
Most came have a menu setting where you can choose between 60 or 50 Hz, but even then its no guarantee you wont see flickering lights.

Not sure is automotive LED lights adhear to the 60/50 HZ, to be honest i think its just do as you bloody well please.

 

[DT MI]

You will probably see the same thing with fluorescent lights as well - again due to the 50/60 HZ cycle.

 

[lacibaci]

Controlling LED brightness using PWM
http://www.waitingforfriday.com/index.php/Controlling_LED_brightness_using_PWM

 

[thancam]

Nope. The flick of traffic light is not 50 hz or 60 hz. It depends on ppl who wrote software for this traffic light but nomaly, it is about 25 or 30 hz. And therefor you cant remove the flick from traffic light.
The flicker on Testa's car: I don't know. But i don't think it involve with power system. And the power system has 50 or 60 hz frequency.
Nomal car, led light don't have frequency. They light continuity !

 

[thancam]

Image's sharp but not colour. Almost like black - white.

 

[jokiin]

LED flicker is something you just have to live with due to the different refresh rate used

 

[DT MI]

...
Nomal car, led light don't have frequency. They light continuity !

I'm not sure that's correct. I'm not an EE so don't claim to know all that much about it but this article seems to says that LEDs can flicker and it's a function of the driver and not the LED itself.

http://www.ledsmagazine.com/article...erstand-the-lighting-flicker-frustration.html

 

[thancam]

I'm not sure that's correct. I'm not an EE so don't claim to know all that much about it but this article seems to says that LEDs can flicker and it's a function of the driver and not the LED itself.

http://www.ledsmagazine.com/article...erstand-the-lighting-flicker-frustration.html

thanks for correcting me. I mistake led light with incandescent bulb

 

[jokiin]

the don't light continuously, it's just that the flicker is generally hard to notice until you're using digital video and frame rates come into play

 

[thancam]

Nomaly, i see signal light's car is a incandescent bulb. They want to save power on Testa car, so they use led light as signal light on Testa car. So that's why they flickering

 

[jokiin]

Nomaly, i see signal light's car is a incandescent bulb. They want to save power on Testa car, so they use led light as signal light on Testa car. So that's why they flickering

LED lights are becoming very common so you'll see this on all sorts of cars these days

 

[SawMaster]

I'm into LED flashlights as a hobby and know something of all LED lighting. Most of these are controlled via PWM and the rates go from low (very visible) to high (kHz range) which is not visible to the eye, but will show up on dashcam vids because of the 'rolling shutter' not being the same frequency of the LED driver and not synchronized to it. Generally older and cheaper LED drivers have low PWM. Newer and better ones are higher rates to avoid customer complaints. It's the cheapest most common way to regulate current to the LED so that it doesn't burn out or overheat. There are other methods but they aren't really practical anymore. The funny thing is that high PWM drivers cost only a few cents more in bulk yet cheap companies prefer that profit over quality and customer satisfaction

Some people are very sensitive to low PWM and some aren't. It can cause various reactions too. It normally doesn't bother me but older Cadillac's tail and brake lights make my eyes hurt so badly I can't be near them, even in my peripheral vision , and even in broad daylight. I've pulled off the road several times just to distance myself from those cars That particular PWM rate and me simply don't play well together. And it's high enough that I can't visually see it. No other LED lights affect me like this or in any other way. I've heard anecdotal evidence of low PWM setting off epileptic seizures in some folks It's something I expect to see being regulated by laws or by engineering standards soon, but it's always going to show up on digital video to some degree no matter what; just the nature of the game.

Phil

 

[Paul Schmehl]

Thanks. That makes perfect sense.

 

[Mozzie]

Nowadays everything is computer controlled. It is easier that way as instructions can be customised, modified, etc. For this reason it is easier to have a computer control the devices rather than have dedicated hardware to operate it. A computer is doing lots of things at once and is addressing each device (eg. light) for an interval in time. This leads to the refresh cycle (pulsing) we are talking about. Reducing the pulse count can also reduce the brightness if required. The pulse count is faster than the human eye can detect but can be apparent when a video is reading these pulses at a different pulse rate.

 

[kamkar]

@SawMaster any man should be judged by the power of his LED torch

I got LED for easy carry, and then HID for O MY GOD or needing to set things on fire.

 

[SteveFL]

LED flicker is something you just have to live with due to the different refresh rate used

LED lighting will also flicker if the voltage received is not clean. Try using an LED light on a dimmer switch that isn't designed for LED lighting. You get flickering as well.