Electric light glare control

Electric light glare control

Intent: 

To minimize direct and overhead glare by setting limits on the luminous intensity of luminaires.

BACKGROUND

Non-diffuse, bright indoor lights create uneven levels of brightness in the visual field. The resulting glare, defined as “excessive brightness of the light-source, excessive brightness-contrasts and excessive quantity of light”, can cause visual discomfort (discomfort glare), fatigue, visual impairment and even injury (disability glare), and can be attributed to either direct or reflected glare. In the case of glare caused by electric light sources, lamps should be shielded based on their luminance. This quantity, often given in cd/m², can be measured directly or calculated from lighting specification sheets with sufficient detail. Light fixtures of greater luminous intensity require a greater shielding angle to reduce the likelihood of creating direct glare for occupants.

Part 1
Luminaire Shielding

The following shielding angles (⍺ = 90 - cutoff angle) must be observed for lamps in regularly occupied spaces with luminance values in the ranges specified:
a.
No shielding required for less than 20,000 cd/m² (including reflected sources).
b.79
⍺: 15° for 20,000 to 50,000 cd/m².
c.79
⍺: 20° for 50,000 to 500,000 cd/m².
d.79
⍺: 30° for 500,000 cd/m² and above.

Part 2
Glare Minimization

At workstations, desks, and other seating areas, the following requirement is met:
a.174
Luminaires more than 53° above the center of view (degrees above horizontal) have luminances less than 8,000 cd/m².