On 21/10/2014 10:54, DerbyBorn wrote:
I have noticed many CCTV cameras have a ring of LEDs around the lens - but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)

They have a reasonable range and the cameras are pretty sensitive so
that they don't need much light to form an image. The total IR output is
a bit less than that of a 1W LED torch and with a wider spread. 20m is
typical working range for small ones and 40m for the better ones.

You don't have to have the LEDs on but in the pitch dark they can be
useful on a moonless night. Rain or snow backscatter is more of a
problem than anything else with the lights being near the lens axis.

--
Regards,
Martin Brown