Glare is excessive brightness that causes visual discomfort, just like when a car blinds you with its headlights at night. 

Glare from unshielded lighting is a public-health hazard—especially the older you become. Glare light scattering in the eye causes loss of contrast, sometimes blinds you temporarily and leads to unsafe driving conditions, for instance. 

Glare can be disabling or simply uncomfortable. It is subjective, and sensitivity to glare can vary widely. Older people are usually more sensitive to glare due to the aging characteristics of the eye. Disability glare is the reduction in visibility caused by intense light sources in the field of view, while discomfort glare is the sensation of annoyance or even pain induced by overly bright sources (Rea 2000). Reducing glare is an effective way to improve the lighting.