In many cases where light impairs vision, it is because it dazzles. This can be caused by either direct glare or reflected glare.

• Direct glare is caused by excessively high luminance, e.g. inappropriate or incorrectly positioned luminaires, unshielded lamps or even windows.
• Reflected glare is caused by light reflecting from shiny surfaces such as monitor screens, art paper or wet roads.
  
  

Glare impairs visual performance

Glare should always be avoided. Both direct and reflected glare undermine visual comfort and affect our sense of wellbeing (discomfort glare); glare also impairs visual performance (disability glare). The effect of direct and reflected glare is similar: both impair perception of the contrasts needed for trouble-free vision.

Direct glare can be avoided by adequately shielding lamps and darkening windows. Reflected glare is reduced by positioning luminaires correctly in the room, by limiting the luminance of luminaires and by the use of matt surfaces.