Effect of image intensifier tube equivalent background illumination on range performance of passive night sight

Effect of increase in equivalent background illumination (EBI) with temperature of second generation (18 mm) proximity focused image intensifier tube on the range performance of a passive night sight has been studied using the image intensifier minimum resolvable contrast model. It has been shown that for ambient temperatures of 40°C and above, the range performance of sight goes down drastically under low-illumination level due to increase in the EBI. Deterioration in range performance is negligible when ambient illumination is relatively high as in case of clear-starlit condition.