10. Factors Effecting Camera Sensitivity

Another key aspect of CCTV Systems is installing cameras that provide usable images in the required lighting conditions. This ranges in extreme from a brightly lit supermarket to a parking lot, lit only by the moon. Camera manufacturers normally provide minimum illumination specifications for their cameras in the best case scenario. Factors that effect the performance of CCTV camera include the following.

• Lens Aperture - Lenses in fact allow only a small percentage of light to reach the camera’s sensor, this is further effected by the
  aperture of the lens to be used. An F1.0 lens allows 20%, an F1.4 allows 10% and F2.0 only allows 5% passed.
• Lens Quality - The quality of the lens determines the efficiency of the light that is transmitted through the lens. Your image quality will be much better when using an aspeherical lens, inplace of a standard lens which will not handled the light as efficiently.
• Camera Housing - The amount of light reaching a camera’s sensor can be reduced by approx 30% when passing through a
  housing’s glass window.
• Surface Reflection - Different surfaces have varying percentages of reflectance. Therefore it is better for a camera’s sensitivity to be focused on a white washed wall (60%) than an empty tarred parking lot (5%). Most manufacturers provide figures using the highest reflectance target surface (90%).
• Spectral Response - Camera sensors and lenses react differently under differing light spectrums.

To summarise in many camera installations one actually requires external lighting in the vicinity of 10 ~ 40 lux to provide a usable colour picture from the camera.