Missing standards regarding light sensitivity measurements make comparison of CCTV-cameras difficult
The leaflet-information on light sensitivity of CCTV cameras repeatedly leads to misunderstandings regarding the real quality of a camera when different types are to be evaluated and compared. As long as there are no standards for the measurement of „light sensitivity“ values it will generally be difficult to compare cameras and their quality based on this information.
Consequently the safest way to evaluate camera qualities is a practical comparison of different models. This method, which is a standard procedure at GEUTEBRÜCK, not only offers a direct analysis of the real light sensitivity, but also allows you to gather information regarding natural colour reproduction, picture sharpness, noise-response, etc.
It is of great importance to mention all relevant parameters which have been considered during measurement
- At which wavelength (Colour temperature) has the value been measured?
- Which lens with which transmission ratio and F-factor has been used?
- Has the AGC been activated or not?
- Has the shutter function been activated during the test?
- What was the output level (IRE) of the camera?
- While working at lowest light sensitivity level – is the video picture noisy or is there still a signal traceable within the noise?
You can see that many parameters can influence the measurement of light sensitivity and consequently the quality of a camera. The more parameters you have, the more efficient are the results in comparing different camera models. It is not only important to evaluate the light sensitivity of a camera but also to analyse its CCD-sensor and its type of digital signal processing. Working at its physical limits both criteria can cause signal distortions or stripes within the picture. Effects like „blooming“, „smear effect“ and „colour interpolation“ can be mentioned as important evaluation factors.
Additional factors: The influence of the picture signal-to-noise ratio
- 0,5 Lux / F1,2 (50 IRE) means that using a lens with the focal ratio F1,2 and a surrounding light level of 0,5 Lux the signal of the picture measured in Vpp still reaches 50% of the standard signal output level.
- Cameras measured with 0,5 Lux / F1,2 (20 IRE) only have to reach signal output levels of 20% of the standard 1 Vpp and often can reproduce the picture only with high noise ratio. The lower the signal output whilst measuring, the higher the amount of noise within the camera picture.
- In case you only have the information 0,5 Lux / F1,2 this might lead to misinterpretations since you do not know whether the signal-to-noise ratio was acceptable during measurement or not.
In the following you will find some typical data sheet information showing how much the value details can vary
- 1/3“ colour camera; DSP; 12VDC; 330 TVL; 0,45 Lux
- 0,02 Lux / F1,2 / using shutter function
- 2 Lux (30 IRE)
- 0,02 Lux / using shutter function 128x