What does Contrast Sensitivity Measure and Depict?

Contrast sensitivity measures the ability to see details at low contrast levels. Visual information at low contrast levels is particularly important:  

1. In communication, since the faint shadows on our faces carry the visual information related to facial expressions. The faint shadows are in motion, thus also motion perception plays an important role.
   
   
2. In orientation and moving, where we need to see such critical low-contrast forms as the curb, faint shadows, and stairs when walking down. In traffic, the demanding situations are at low contrast levels, for example, seeing in dusk, rain, fog, snow fall, and at night.
   
   
3. In everyday tasks, where there are numerous visual tasks at low contrast, like cutting an onion on a light coloured surface, pouring coffee into a dark mug, checking the quality of ironing, etc. There are also many occupations where very good contrast sensitivity is required. One of them is finishing the surface of white boats and yachts because the quality of the surface is evaluated visually.
   
   
4. In near vision tasks like reading and writing, if the information is at low contrast as in poor quality copies or in a fancy, barely readable invitations, or pastel coloured pictures.

If a person can see details at very low contrast, his or her contrast sensitivity is high and vice versa. Depending on the structure of the stimulus used in the measurement, either gratings of different size or optotypes, contrast sensitivity of a person gets different values.