Why do performance cars lights flicker?

"55Buick, Oversteer Scientist" (55Buick)
05/12/2014 at 21:56 • Filed to: Flickering lights

Whenever Top Gear/EVO/Motor Trend/etc. do a review of a supercar, there are invariably some slow-mo drift shots. In all of them, the lights on the cars seem to flicker as they drift. Anyone else notice this, and does anyone know the purpose?

DISCUSSION (26)

FrankenBlaster > 55Buick, Oversteer Scientist
05/12/2014 at 21:58

I could be wrong, but I always assumed that the lights flickered fast enough that it wasn't noticeable to us, but it gets caught out of phase with the standard 30/24/whateverfps of the camera. Like when you film a plane's propeller, or film a tv screen/monitor.

Nick, Drives a Cobalt LT > 55Buick, Oversteer Scientist
05/12/2014 at 21:59

LED lamps are on and off, they always are on and off, never constant on, the frame rate on the camera is differing from the frame rate of the lamps, causing that.

Same tihng happens when someone has them behind you in your car and you hit a bump or something you see it in the mirror.

Crest > 55Buick, Oversteer Scientist
05/12/2014 at 21:59

It has something to do with the camera's shutter speed and flickering LED's. To the normal eye LED's don't flicker but to a camera, it catches moments of the flickering. I hope it makes sense because that's the best way i could put it

Arch Duke Maxyenko, Shit Talk Extraordinaire > 55Buick, Oversteer Scientist
05/12/2014 at 22:00

LED's flicker naturally, but faster than the eye can see. The frame rate of the camera is faster than the naked eye so the blink becomes perceptible.

Soloburrito > 55Buick, Oversteer Scientist
05/12/2014 at 22:01

The frames per second of the camera is faster than the refresh rate of the LED lights.

For Sweden > FrankenBlaster
05/12/2014 at 22:01

Off topic, but oppo needs TCGR deets

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > 55Buick, Oversteer Scientist
05/12/2014 at 22:01

It's the frequency those lights flash at is different than what the camera is filming, so it looks like it's flashing on film, but not real life. It's common with LEDs and fluorescent tubes.

Jake - Has Bad Luck So You Don't Have To > 55Buick, Oversteer Scientist
05/12/2014 at 22:01

The LEDs are running on what's called a "duty cycle", wherein they aren't on all the time. A 50% duty cycle would mean that the LED is on half of the time and off half of the time. The reason for this, if I remember right, is so that the LED can be run at a higher brightness than would normally be possible at 100% duty (always-on) without burning up the diode.

The flickering you see is just the camera happening to capture a frame while the LED is turned off during its duty cycle. I had to explain this concept to my parents when reviewing footage of my car autocrossing, and they thought my third taillight was failing or something because of the flicker.

gabbo241 > 55Buick, Oversteer Scientist
05/12/2014 at 22:03

I don't think the lights are actually "flickering" in an intentional way that would be perceptible to your eyes. I think what's happening is that the LED lights turn on and off continuously at a very high frequency, and the frame rate of the cameras being used is in and out of sync with the LEDs being on or off. Hence the lights appear to flicker. But if you were there watching it, you wouldn't see the lights flickering. I think its a similar effect as when wheel spokes appear to rotate in the wrong direction.

cabarne4 > 55Buick, Oversteer Scientist
05/12/2014 at 22:04

Wow... Looks like you got your answer pretty fast.

But just in case you missed it, it's because LED lights are not "always on". Instead, they pulse on and off, faster than the human eye can recognize. However, camera refresh rates catch the flicker.

Devlin Munion > 55Buick, Oversteer Scientist
05/12/2014 at 22:04

Taken from the below Question/Answer.

"Some LED displays are multiplexed which means they are flashing on and off in a way that is not discernible to the naked eye and produces no visible flicker. However when the LEDs are viewed on TV they aren't in sync with the TV frame rate and as a result appear to flicker. It's like watching wagon wheels on an old western movie, the wheels appear to go backwards or forwards depending on how they sync with the 24 frames a second rate of the film, it's the same with the flicker of multiplexed LEDs and 25/30 frames a second TV pictures."

https://answers.yahoo.com/question/index…

FrankenBlaster > For Sweden
05/12/2014 at 22:05

You have my word I'll do a write-up soon. I wanted to give it some time to make sure I knew what I could/couldn't say about what I do, and I've been at the track for some long hours the past few days so when I get some time I'll put something together.

55Buick, Oversteer Scientist > cabarne4
05/12/2014 at 22:06

I sure did! And thanks for the answer, I never knew they were on/off. I guess I learn something new every day!

Soloburrito > Soloburrito
05/12/2014 at 22:11

ok i think others here have it more right than my answer. But yeah the point is LEDs generally flicker faster than human eyes can perceive.

cabarne4 > 55Buick, Oversteer Scientist
05/12/2014 at 22:25

Refresh rate on cameras can make all sorts of things look weird. Check out light aircraft dash cams — the propeller seems to stand still in a lot of videos, because the video camera takes a frame shot when the propeller is about in the same position again. Cell phone cameras make ceiling fans look weird, if you want an example you can play with at home. Screens / monitors / TVs often have refresh rates that differ from camera rates as well, which is exactly the same as the racecar effect. Point your phone at the TV and you'll see what I mean.

CRider > 55Buick, Oversteer Scientist
05/12/2014 at 22:26

Florescent lights also flicker.

It's a "Porch-uh" > cabarne4
05/12/2014 at 22:43

The effect is known as "aliasing." Also happens with wheels when sometimes it looks like they slow down and/or start spinning backwards. Just a matter of the frequency of the camera coming into alignment with the frequency of the spinning (or flashing) object. As a guy who shoots video I find it terribly annoying.

cabarne4 > It's a "Porch-uh"
05/12/2014 at 22:44

Ah, I was sure there was some term for it. Guess I learned something today, too!

It's a "Porch-uh" > cabarne4
05/13/2014 at 00:04

Kinja'd!!!

Clown Shoe Pilot > 55Buick, Oversteer Scientist
05/13/2014 at 08:04

I have noticed a similar behavior w/ our scoreboard at the race track.

The two photos below were taken probably within milliseconds of each other. Notice that in the first, positions 8 and 10 on the scoreboard look dim. On the second, it's 6, 7, and 10.

If you watch the scoreboard on the CCTV cameras, the digits fade in and out because their flicker rate and the frame rate of the camera are just barely out of sync.

Kinja'd!!!

Rickster3rd ¯\_()_/¯ > 55Buick, Oversteer Scientist
03/30/2015 at 10:17

I know I am late to this discussion but thanks for the answer. As I was watching a recent Top Gear I noticed the same thing on a new Lamboghini Huracan and wondered the same thing. My initial thought was since supercars are hyperfast that is a warning to drivers in the left lane to move over.

JDIGGS > 55Buick, Oversteer Scientist
07/29/2015 at 03:59

Correct me If I’m wrong but this is not the “LED FLICKER” we are seeing but many racing cars have a flashing / rotating flashing brake light, I think it’s a thing in European and I’ve seen it with specialized police vehicles.

Definitely have seen this with my eyes in person.

LEDs_For_Lfe > Arch Duke Maxyenko, Shit Talk Extraordinaire
02/08/2016 at 13:42

YESSSSSS SO SHORT/SWEET BUT MAKES ME FINALLY UNDERSTAND THE RACING CAR FLICKER!!!!!!!

LEDs_For_Lfe > 55Buick, Oversteer Scientist
02/08/2016 at 13:43

I’ve always wondered the same thing!!!

thatcarguyj > cabarne4
07/06/2017 at 03:06

so the do this to save power?

Richard Bell > cabarne4
08/01/2017 at 19:07

LEDs themselves don’t cause the flicker. The electronic circuits which control the LEDs often do so by switching the LEDs on and off at a fast rate, thus introducing flicker (which some people see and others don’t), but if you run an LED purely off a DC supply it doesn’t flicker at all.