Will the attached 100Hz flickering light output cause a problem for CCTV? - Page 1
Forum section: electronics / beginners

author: ocset
author_rank: Super Contributor
timestamp: August 27, 2018, 06:44:24 pm
content: Hello,Supposing there is a LED streetlight which flickers as in the attached. (that’s actually the light output, not a voltage). As you can see, the light output actually goes to zero every 10ms.Will this cause a problem for CCTV cameras at night ?Will this cause a problem for Number plate recognition cameras at night?Will this cause a problem for police dash-cams at night?Supposing if the exposure time is 1ms, and it takes 1 picture per second, then surely in theory the images could all be black?

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: August 27, 2018, 07:10:57 pm
content: Your best bet is to just grab a CCTV camera (type & model you are planning to use) and try it in real life conditions. This is because different cameras use different sensors so the only way you can be certain in anything is to just try it out.

author: Gyro
author_rank: Super Contributor
timestamp: August 27, 2018, 07:23:08 pm
content: You've already asked...https://www.eevblog.com/forum/projects/100hz-flicker-in-lighting-is-a-problem/msg1775726/?topicseen#msg1775726P.S. That .jpg you've attached is just full wave rectified AC waveform,notthe light output waveform of an LED Streetlight.

author: janoc
author_rank: Super Contributor
timestamp: August 27, 2018, 10:24:10 pm
content: Treez, why are youstilltrying to find a justification that your crappy 100Hz flickering LED is somehow an acceptable design? All that after two pages of discussion in that other thread where it was clearly explained to you that cameras are likely the least of your problems there!Put a bloody capacitor at the output of that rectifier and be done with it. This is beyond ridiculous. What will you do when your employer gets sued because someone got distracted by that high powered stroboscope of yours and crashed their car?BTW normal CCTV camera will likely not capture the individual flicker (they run much slower than 100Hz) but the automatic gain control will likely be mightily confused by that flicker, with some frames being overexposed and some underexposed.

author: eliocor
author_rank: Unknown
timestamp: August 27, 2018, 10:40:41 pm
content: DEAR treez PLEASE DO NOT GIVE ME A 'THANK': I found offensive to your person your way of thanking everyone!!!Quoteto my knowledge (at least in Italy*) every plate recognition camera (also Police ones) during night works:- using pulsed infrared light (at various levels to be sure to not be fooled)- using the retoreflector treatment on the plate to get an high image contrastThe same can be said for almost any CCTV camera: under a certain level of light they disable the IR cutoff filter and turn to IR vision.So your question(s) [at least for those case(s)] are useless because visible light will not affect camera vision.*) I think also in the rest of Europe, being car plates almost "unified":https://en.wikipedia.org/wiki/Vehicle_registration_plates_of_the_European_Union

author: CM800
author_rank: Frequent Contributor
timestamp: August 27, 2018, 10:44:56 pm
content: Quote from: eliocor on August 27, 2018, 10:40:41 pmI'm so confused. What's wrong with him thanking people for their response...How is it... offensive?

author: janoc
author_rank: Super Contributor
timestamp: August 28, 2018, 07:24:07 pm
content: Quote from: eliocor on August 27, 2018, 10:40:41 pmUm, careful!Most cameras cannot "disable" the IR filter - that is a physical piece of glass in front of the sensor and most cameras don't have any mechanical means to move it out of the way. In fact, many cheap cameras/lenses have the IR filter even glued on. The "IR vision" with CCTV typically only means increased gain (and noise) and turning on an IR illuminator (a ring or panel of IR LEDs).Visible light willvery much affectsuch camera - they don't filter visible light at all, so if you shine a bright light there, it will saturate the sensor, rendering the image useless until the automatic gain control kicks in again (never seen an image of a security camera recording an approaching car with the lights on?). The sensor doesn't have any special "IR" mode - normal CCD and CMOS sensors are simply sensitive in the near infrared as well so they can see the reflected IR light from the illuminator. That's also why the IR filter is there in the first place, otherwise you would get a reddish cast over the image due to the saturation with IR during the day.

author: eliocor
author_rank: Unknown
timestamp: August 28, 2018, 07:53:43 pm
content: It was an oversimplification...Even because it is clear (see your previous answer) that treez does not care at all to read what other people write/suggest/explain! He thanks only!@CM800: So I can write the crappiest answer and I'm sure I will get a 'thank' without any hitch

author: CM800
author_rank: Frequent Contributor
timestamp: August 28, 2018, 08:07:09 pm
content: Quote from: eliocor on August 28, 2018, 07:53:43 pmYes

author: BradC
author_rank: Super Contributor
timestamp: August 29, 2018, 12:32:16 am
content: Quote from: janoc on August 28, 2018, 07:24:07 pmEven the cheap shit generic Chineseium cameras (Hikvision I'm looking at you) have motorised IR filters and have had for years, so I'd suggest (based on years of experience of actually testing them) that "most cameras have a switchable IR filter".

author: ocset
author_rank: Super Contributor
timestamp: August 29, 2018, 05:25:51 am
content: Thanks, from these posts it seems that severe 100hz flickering light, which goes to zero every 10 milliseconds, is certainly not a "definite" for ruining CCTV images.The Automatic Gain control will take care of it...it seems.I wonder what the shortest exposure time is for a general CCTV camera?If its >10ms, then there really is no problem at all.

author: BradC
author_rank: Super Contributor
timestamp: August 29, 2018, 10:25:07 am
content: Shortest usable shutter speed is about 1/60th of a second. Longer than that and things start to smear on a budget camera. Quality cameras don't go down that low unless there is no artificial light present.I have cameras here that will still use 1/1000 at night under streetlight conditions and struggle with strobing on HPS, so an unfiltered led will strobe to shit. Having said that, if the security consultant is any good they'll characterise the light source for both consistency and spectrum to ensure it will work with the specified cameras.Frankly I hate LEDs in cheap shit light sources, but you can spend money on better lights or spend money on better cameras, more often than not a $4K camera and lens is much cheaper than upgrading the lighting.

author: janoc
author_rank: Super Contributor
timestamp: August 29, 2018, 06:52:45 pm
content: Quote from: BradC on August 29, 2018, 12:32:16 amOK, taking back the "most". I am more familiar with industrial and machine vision cameras than specifically surveillance products and there this kind of functionality is not at all common.

author: ocset
author_rank: Super Contributor
timestamp: August 29, 2018, 07:31:26 pm
content: QuoteThanks, thats 16ms approx exposure time.Do you know what proportion of CCTV camers in use at night (in say city centres) go below 10ms exposure time?And how many go below 5ms exposure time?

author: eliocor
author_rank: Unknown
timestamp: August 29, 2018, 08:01:00 pm
content: 0.0237015%0.0033377%@CM800: QED !!!

author: BradC
author_rank: Super Contributor
timestamp: August 29, 2018, 11:25:37 pm
content: Quote from: treez on August 29, 2018, 07:31:26 pmLots. Most cameras will wind the exposure time down as far as 1/10000 to control exposure. Cheaper cameras with smaller imagers are pretty insensitive and want lots of light though,so will struggle to go below 1/60 at night. Plenty will though.Frankly I think you're approaching the problem from the wrong end, but that seems to characterise most of your posted topics on this board.