What Does Fill Factor Mean When Talking About Photography?

Fill factor is the ratio of the light sensitive area of a pixel to the total area of a pixel on a digital imaging sensor. The higher the fill factor, the more sensitive a sensor is to light. Sensitivity directly effects the ability of a camera to capture images in low light situations without having to use either long exposure times, which can lead to loss or sharpness, or high ISO levels which can lead to excess noise. Light sensitivity and performance is one of the most important factors to consider when buying any camera and a higher fill factor is an indication of improved light sensitivity.