An unshielded lamp in the direct line of vision is a potential source of direct glare caused by excessive luminance. There are two ways of avoiding direct glare: either the lamp is shielded, e.g. by the housing itself or by fitting solid vanes or louvres, or the high level of luminance is reduced through the use of opal or prismatic diffusers.
In the simplest case reflector luminaires are shielded by vanes made of metal or plastic placed parallel and at right angles to the axis of the lamp. The luminance limit angle is dependent on the combination of vane height h and vane spacing a.
|
Range of mean luminance cm/m2 |
Direct glare cut-off class |
||||
|---|---|---|---|---|---|
|
A |
1 |
2 |
3 |
||
|
Fluorescent lamps |
L = 2·104 |
20° |
10° |
0° |
0° |
|
Compact fluorescent lamps |
2·104 < L = 4·104 |
20° |
15° |
5° |
0° |
|
High pressure discharge lamps with fluorescent or matt bulbs, low-pressure sodium lamps |
4·104 < L = 50·104 |
30° |
20° |
10° |
0° |
|
High pressure discharge lamps with clear bulbs or tubular types, incandescent lamps with clear bulbs |
L = 50·104 |
30° |
30° |
15° |
10° |