Do speed cameras work in the dark?
Discussion
Drove past a mobile the other day (one that was being pointed at me). Nothing unusual I hear you say but it was pitch black!! I have only ever seen these things used during the day so do they work?? I would have thought that my headlights would have 'blinded' it from seeing my plate??
....not that I'm worried at all!!!!
....not that I'm worried at all!!!!
Yes, in fact they would probably work even better because there is less ambient light (a better quality of return signal). The laser outputs a narrow range of light and the photodiode has an equally narrow filter, therefore all it sees is the light reflected from the target, headlamps being lit etc. don't really make a difference either.
Also the user's manual for the 20:20 says that a number plate only provides a "marginal" benefit due to it's reflectivity. In practice you can get a return from nearly anthing whether it looks reflective or not (even trees).
Gareth
>> Edited by g_attrill on Wednesday 9th March 22:09
Also the user's manual for the 20:20 says that a number plate only provides a "marginal" benefit due to it's reflectivity. In practice you can get a return from nearly anthing whether it looks reflective or not (even trees).
Gareth
>> Edited by g_attrill on Wednesday 9th March 22:09
I'm sure someone (cptsideways??) has shown that headlights decrease the range of laser speed detection. After all, headlights have a very high output in the infrared wavelengths, and whilst not modulated in the same way as the speed gun laser, will almost certainly be modulated by vibrating fillaments and the car's body motion etc. and causing a much higher background noise level.
) but if you cannot identify the car it is not much use.I was sat in traffic on the way home tonight and tried to read cars number plates as they approached. Now I could not see anything until the car was by the side of me but I'm guessing that they may have some image enhancing stuff??
Plus, if I get a NIP I will need to see the photo to determine who was driving because my missus and me were on the same road, in the same car about 10 minutes apart. Normally a forward facing camera would get this no problem but what do I do if I can't see the driver? Aparantly I have a legal right to determine who the driver was...do I just guess??
Plus, if I get a NIP I will need to see the photo to determine who was driving because my missus and me were on the same road, in the same car about 10 minutes apart. Normally a forward facing camera would get this no problem but what do I do if I can't see the driver? Aparantly I have a legal right to determine who the driver was...do I just guess??
Well our local scammers have invested in night vison scameras:
www.safecam.org.uk/news/news_story.asp?id=241
Obviously got too much cash
www.safecam.org.uk/news/news_story.asp?id=241
Obviously got too much cash
Its highly unlikely they work in the dark, for the following reasons:
Optics: Wide open iris, very low depth of field, very hard for the cameraman to focus correctly when zoomed. Also, headlights would cause multiple instances of lens flare.
CCD: CCD isn't powerful enough to record the low light being reflected off the number plate. If you made it more sensitive, you'd get large amounts of bleed up and down the CCD.
Can't form prior opinion of speed: Unless the carriageway is brightly lit, how can anybody guess the speed of the vehicle?
Its for these reasons that Truvelo cameras have flash units.
Optics: Wide open iris, very low depth of field, very hard for the cameraman to focus correctly when zoomed. Also, headlights would cause multiple instances of lens flare.
CCD: CCD isn't powerful enough to record the low light being reflected off the number plate. If you made it more sensitive, you'd get large amounts of bleed up and down the CCD.
Can't form prior opinion of speed: Unless the carriageway is brightly lit, how can anybody guess the speed of the vehicle?
Its for these reasons that Truvelo cameras have flash units.
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