100Hz flicker in lighting is hazardous to humans?

[Flyback]

Hello,
Regarding LED streetlighting flickering at 100Hz…..this would only affect night-time security cameras and traffic cameras, and police dash-cams, including number plate recognition cameras, if the shutter speed was slower than 1/100th of a second (10ms).
So do you know what is the shutter speed of these type of security cameras? The www doesn’t tell.
Obviously, a Frame Rate of 25 per second, and a shutter speed of 1ms could potentially record for a long time in the prescence of 100Hz flickering LED streetlighting and show nothing at all (total blackness).
However, if all such security cameras automatically increase shutter speed to take in enough light, then this could be overcome…because going up to 10ms shutter speed would solve the problem…however, if this shutter speed is too slow for a fast moving object, then there would be movement blur. A man running at 10m/s travels 10cm in 10ms….that could cause unacceptable movement blur…and it would be even worse for a vehicle which moves faster.
Maybe all such security cameras automatically shift the phase of the “shutter openings” in order to accommodate the effect of 100Hz flickering streetlighting with fast shutter speeds? (ie time it so each shutter opening corresponds to the mains peak point, where the flickering light is most bright)

 

[gophert]

Hello,
Regarding LED streetlighting flickering at 100Hz…..this would only affect night-time security cameras and traffic cameras, and police dash-cams, including number plate recognition cameras, if the shutter speed was slower than 1/100th of a second (10ms).
So do you know what is the shutter speed of these type of security cameras? The www doesn’t tell.
Obviously, a Frame Rate of 25 per second, and a shutter speed of 1ms could potentially record for a long time in the prescence of 100Hz flickering LED streetlighting and show nothing at all (total blackness).
However, if all such security cameras automatically increase shutter speed to take in enough light, then this could be overcome…because going up to 10ms shutter speed would solve the problem…however, if this shutter speed is too slow for a fast moving object, then there would be movement blur. A man running at 10m/s travels 10cm in 10ms….that could cause unacceptable movement blur…and it would be even worse for a vehicle which moves faster.
Maybe all such security cameras automatically shift the phase of the “shutter openings” in order to accommodate the effect of 100Hz flickering streetlighting with fast shutter speeds? (ie time it so each shutter opening corresponds to the mains peak point, where the flickering light is most bright)

Do ANY cameras record at 25 frames per second? I've never heard of that.

Slower camera speed is better so you have no concern. Slower speeds will allow the photo to be taken over multiple flashes.

I don't understand your concern, there are a fractional number of police that will be unhappy vs the rest of the driving public that will be happy when their license plate does not appear so you could become a folk hero. Unfortunately,, I don't know of a single license plate camera that relies on street lamps for illumination. Most every one that I've seen include a powerful flash to go with it - often in IR so drivers don't even see it.

 

[Nigel Goodwin]

Do ANY cameras record at 25 frames per second? I've never heard of that.

Every PAL video camera there is does, and NTSC ones record at 30 frames per second. ANPR cameras are video cameras, and not stills cameras - there's certainly no flash involved, IR or otherwise, as they usually work at far too great a distance for flash to be effective, and flash isn't much use with video anyway. I was playing with two cameras removed from ANPR last year, very long focal length so not much use for other purposes, unless you get a different lens.

Speed cameras (GATSO etc.) use stills cameras and flash though - and I think actual film cameras are still fairly common.

But this all seems a lot of panic about nothing, street lighting (and home lighting) has always flickered at 50/60/100/120 Hz, and yet the world still goes round, and security and ANPR cameras continue to function.

 

[ronsimpson]

street lighting (and home lighting) has always flickered at 50/60/100/120 Hz

Many lights have little flicker.
edited---sorry for the big picture. It looked small when I copied it.

 

[Diver300]

You can get all sort of artefacts. Youtube link.

I used a phone camera to record the head-up display in a car, and initially it was completely missing from the recording. The lighting level was bright, from sunlight, so the camera didn't increase the shutter time. The head-up display was flickering at nearly an exact multiple / fraction of the camera frequency. Also the camera had a shutter time far shorter than the frame rate, and the head-up display was only on for a small fraction of the time, and when I started recording, they weren't happening at the same time.

As I continued recording, the head-up display started to become visible, and over about 30s became extremely bright on the screen, far brighter than it looked without using the camera, after which it faded to missing over another 30 seconds.

The frequencies of the display and the camera were clearly very slightly different, so the shutter period of the camera and the lighting period of the display had slowly aligned and then slowly drifted out of alignment.

There could be massive issues with variable road signs. The variable speed limits on some motorways in the UK are light-up signs. They only light up when there is a reduced speed limit, so they are often dark. They flicker, so recording them at 1000 fps will have plenty of frames with them black when a lower speed limit applies. Like my phone camera, cameras in cars may be fooled.

 

[Diver300]

Many lights have little flicker.
edited---sorry for the big picture. It looked small when I copied it.

A lot of LED lighting is sufficiently smoothed that the flicker is hard to detect, and the flicker is down at or below the flicker level of incandescent lights.

 

[Flyback]

But this all seems a lot of panic about nothing, street lighting (and home lighting) has always flickered at 50/60/100/120 Hz, and yet the world still goes round, and security and ANPR cameras continue to function.

Thanks but LED streetlights powered by these, and many others, have no flicker..
https://www.docs.lighting.philips.c...5W_0.3-1.0A_S1_230V_C170_sXt_929001535506.pdf

Also, sodium streetlights barely flicker due to the persistence of them
Also, induction lamp streetlighting has no flicker.

So CCTV would not have difficulty with these for these reasons.

Electrolytic capacitor free streetlights flicker severely at 100Hz..(unless they use Film caps, but most dont because films are too expensive)

 

[Beau Schwabe]

The only thing I see (no pun) that might be harmful is that it could be a distraction while driving if you are able to see the flicker. Try chewing something crunchy like ice, clicking your teeth together, or turning your head suddenly... this will improve your chances of being able to "see" the flicker.

 

[ronsimpson]

My wife has problems with ceiling fans with lights that flicker. I think it works like a RF mixer. You inject 2 frequencies and get back four.

I hate flickering lights when they move. (some auto lights) but when I am moving and the flickering light is stationary it does not bother me.

 

[atferrari]

or turning your head suddenly... this will improve your chances of being able to "see" the flicker.

I hate flickering lights when they move. (some auto lights) but when I am moving and the flickering light is stationary it does not bother me.

I have seen that effect in tail lights of cars moving ahead of me, precisely when turning my head. Never took care of the brand but would be interesting to make a list. Ah, LED lights always, that is, modern vehicles.

 

[gophert]

I have seen that effect in tail lights of cars moving ahead of me, precisely when turning my head. Never took care of the brand but would be interesting to make a list. Ah, LED lights always, that is, modern vehicles.

Mostly (exclusively?) GM cars with LED twilights. The society of automotive engineers is aware of it. Technically, it is not allowed to have "flashing" lights on a car in the US except for turn signals and daytime headlight modulators on motorcycles. GM claims it is not flashing because it cannot be seen - even though every GM engineer I've spoken to agrees that they flash.

 

[Reloadron]

Mostly (exclusively?) GM cars with LED twilights. The society of automotive engineers is aware of it. Technically, it is not allowed to have "flashing" lights on a car in the US except for turn signals and daytime headlight modulators on motorcycles. GM claims it is not flashing because it cannot be seen - even though every GM engineer I've spoken to agrees that they flash.

Gopher, you got anything on that? As to the flashing? Here is why I ask. I replaced my stop (brake) lights on the back of my older bike with some LED lighting. The brake lights offer me several options and the one I am currently using is when I apply my front or rear brake my brake lights will flash 3 times and then a solid light. The idea being to make a braking bike more noticeable. This is all DOT approved and braking systems like this are common.

Myself and a friend were stopped in Streetsboro, Ohio where many of the police have little to do. My friends bike is set for 6 flashes and then steady which the cop claimed as illegal and only law enforcement cars could have flashing lights with that effect. I would guess about a 0.5 second flash rate. If I am driving my truck and as I approach a light or stop I can pump my brakes a few times and get the same effect which I presented to the now obviously confused police officer. The cop had no choice but to agree and with no reason to have stopped us bid us a farewell and have a good day. Here is a clip of Tenn law:

(b) (1) Every motor vehicle shall be equipped with two (2) red tail lamps and two (2) red stoplights on the rear of such vehicle, and one (1) tail lamp and one (1) stoplight shall be on each side, except that passenger cars manufactured or assembled prior to January 1, 1939, trucks manufactured or assembled prior to January 1, 1968, and motorcycles and motor-driven cycles shall have at least one (1) red tail lamp and one (1) red stoplight. No non-emergency vehicle shall operate or install emergency flashing light systems such as strobe, wig-wag, or other flashing lights in tail light lamp, stoplight area, or factory installed emergency flasher and backup light area; provided, however, that the foregoing prohibition shall not apply to the utilization of a continuously flashing light system on a motorcycle. For the purposes of this part, "continuously flashing light system" means a brake light system on a motorcycle in which the brake lamp pulses rapidly for no more than five (5) seconds when the brake is applied, and then converts to a continuous light as a normal brake lamp until such time as the brake is released.

My understanding is as addressed above brake lights like this are legal in all 50 states. When I hear "strobe" I tend to think very fast but at 0.5 Hz or 1 Hz I like to think pulsed.

Ron

 

[gophert]

My understanding is as addressed above brake lights like this are legal in all 50 states. When I hear "strobe" I tend to think very fast but at 0.5 Hz or 1 Hz I like to think pulsed.

I would say "very fast" is any rate (frequency) that lets YOU say that you were not breaking the law. I must admit, I only read the law on the modulating headlamp for motorcycles as a known exception to allowable flashes, I didn't know that these types of flashing taillights were allowed as a second exception. I like it.