|What is glare?|
|Glare is simply the excessive brightness experienced by looking directly into a light fixture.|
|Some definitions are in
Luminous Intensity is the amount of light a luminaire emits in a given direction. The candela is the unit of measure of luminous intensity. This information is readily available for most all commercial grade luminaires from their manufacturers.Brightness is the human perception of luminous intensity. As luminous intensity increases at a given viewing angle, we see it as ‘getting brighter’. Glare is simply the point where brightness becomes excessive.
|Where does glare come from?|
|Poorly shielded luminaires or improperly aimed floodlights may appear ‘glarey’ well beyond the extents of the property line. The evaluation of glare is highly subjective and the most difficult of the three objections to quantify.|
|What causes glare?|
|We perceive brightness through contrast. In other words, we see the difference in luminous intensity between a light source and its background. This is why headlights are blinding at night and barely noticed during the day. A luminaire may seem glarey against a black sky, but not so if it stands in front of a building or wall that is illuminated. The challenge here is that luminous intensity and brightness do not have a simple one-to-one relationship. The human eye / brain response is neither linear nor predictable. We each perceive brightness somewhat differently. This situation is what makes the topic so complex. What we do know, though, is that brightness is related to luminous intensity and also to viewing distance (the closer we are, the brighter it appears).|