What Can You See in the Dark? The Effects of Contrast, Light, and Age on Contrast Sensitivity in Low Light

Contrast sensitivity is the ability to read words which have low contrast with the background. How much light is needed to identify letters of different contrast levels at low levels of light? How does age affect contrast sensitivity? A testing card was created with 25 letters, five at each of five different levels of contrast ranging from 20% to 3% saturation. We hypothesized that subjects would be able to read the five letters at 20% saturation with 50 lux of light, and the younger subjects would be able to read more of the letters than the older subjects. Fifty subjects, ages 10 to 75, participated. Participants were asked to identify any letters they could read at each of six levels of low light, ranging from 0 lux to 50 lux. With more light, there was improvement in the ability to see the letters. There was no linear relationship between age and contrast sensitivity; however, there was a noticeable decrease in some of the adults’ abilities to identify the letters. This research can be applied to improving safe driving at night or in situations, such as restaurant settings, where print must be read in low light, and it is important for accommodating people with certain vision impairments.