Low Lux

Low Lux levels – how well a camera performs at night. Or so you would assume...

Many people selling CCTV cameras quote a minimum lux figure for their cameras. This is supposed to give you an indication of how well the camera performs in low light conditions or when filming using built-in infrared illumination. It will be quoted in Lux, usually something like 0.1, 0.01 or even 0.001 Lux. If the camera is fitted with IR (infrared) illumination then some people quote a minimum lux figure of 0 which is a bit of a cheat. All IR-equipped cameras can film in 0 lux but we are interested in how sensitive the electronics are.

In theory the lower the minimum lux level the better a camera performs at night or in low ambient light conditions. There is a problem though, what do you take as an acceptable image when determining your low-lux figure?

We need to get a little bit technical here and talk about something called an IRE (institute of radio engineers) number. Put simply an IRE of 1 can only tell the difference between black and white, an IRE of 100 shows white as pure white, black as jet black and has all the shades of grey in between. When testing for low lux you need to determine what your minimum accepted image will be. We generally work on IRE 50 but some people will go much lower than that. There are no industry-wide datums.

The other thing to consider is what lens was used for the test and what is fitted to your CCTV camera. If a lens with an incredibly wide aperture was used during the test then the results will be flattering compared to the smaller aperture lens fitted to the actual CCTV camera.

It’s a bit like measuring the 0-60mph time on a car. You assume everyone tests on a flat road but in the world of CCTV, some people will measure whilst driving down a steep hill so don't take the numbers too literally.