Glare appears in the case of very high luminance or large luminance contrast often due to lack of shielding from a window, reﬂection or from direct sight of the LED light sources in the luminaire. Normally, the eye adapts to any lighting situation, but if the lighting of the object or its background is too bright or the contrast is too great, vision suffers by glare. There are two types of glare:
Disability glare, which affects the ability to see and is produced by high luminances in a low luminance scene, typically by point light sources such as bright spotlights aiming at the observers eye, or by large area sources such as a bright LED panel.
• Discomfort glare, which appears in the form of visual discomfort without affecting the ability to see.Discomfort glare is quantiﬁed by the Uniﬁed Glare Rate limit values (UGRL) ranging from UGRL 10 (not noticeable) over UGRL 16 (unpleasant) to UGRL 28 (terrible). The standard EN12464-1 recommends UGR limits for speciﬁc types of rooms and applications (see table 1). Discomfort glare can cause an ergonomically incorrect sitting position (in an attempt to avoid the glare), fatigue and headaches.
The standard EN12464-1 also speciﬁes minimum shielding angle in all directions depending on the lamp luminance. For indoor installations disability glare is rare while discomfort glare might often appear.
With the small size of LED lights and their corresponding brightness, it is recommended to be aware that glare may appear or even cause eye injury if users look directly at the LED light source for a long time.
Glare can be avoided by:
• Lighting design without sharp transitions/contrast
• Control of the light from windows (e. g. with blinds or thin curtains)
• Providing the building with a ﬁxed shield for high sun
• Manual control of the window shields (e. g. many people want to see the sunlight on a winter day)
• Installation of reﬂective or absorbent glazing on windows. Coloured glass should be avoided because it reduces light in cloudy weather periods
• Bright ceilings, panels and walls (e. g. provided by up-lighting with good light distribution)
• Use of soft diffused lighting in rooms with data screens
• Lighting directed at working areas
• Use of larger light sources with less light concentration
• Partial use of up-lighting
• Use of diffusers and shutters in luminaires
• Shielding of lamps from the eyes at normal viewing angles with even light distribution
• In case of doubt about glare from a lamp, a small mirror might be placed in the working and the lamp moved until it is no longer visible in the mirror