• Glare on a computer screen comes from light reflecting off of the surface of a monitor. Excessive glare on a computer leads to physical harm, such as eye fatigue, and may reduce your productivity when using a computer, according to All About Vision. Anything that gives off light can cause, and even reflections off of other surfaces can produce problems.
  
  

Direct Light

• Direct sources of light are the main cause for computer glare, according to the Occupational Health and Safety Administration. Some common ways that direct light gets into a room are through windows and lighting around the room, especially lights on the ceiling. Desktop monitors, especially CRT monitors, are more prone to glare than LCD monitors because their screens are made of glass. Do not assume, however, that LCD monitors are glare free---32 percent of LCD owners complained of glare problems in a 2000 3M survey.
  
  

Secondary Sources of Light

• Even if you strategically position your computer away from direct light you can still have glare problems. Direct light that hits other surfaces around your work environment, such as walls and pictures in frames, can then hit your computer screen, according to Doctor Ergo.
  
  

Settings

• The settings on a monitor may not necessarily cause computer glare, but they can determine how prescient glare is, according to Cornell University. A black background, for example, shows more glare than white backgrounds. In sufficiently bright sources of light, the settings on the computer have a negligible effect on the severity of glare.