Light Distribution - Thorn Lighting

Light distribution categories
Categorizing of luminaires due to their light distribution:
Light distributions of luminaires are categorized by a three character code.
One letter followed by 2 numbers. eg: A10
At first the total lumen light output distribution from each luminaire must be divided in:
- the lower area Ф L
- the upper area Ф U
upper area Ф U
Luminaire
Luminaire mounting level
lower area Ф L
Now Ф L and Ф U must be considered in relation to the total light output Ф T from the
luminaire in all directions.
Ф L
That means φ L = ———
Ф T
Ф U
and φ U = ———
Ф T
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Light distribution categories
Herewith a first classification Table 1 is possible for the first letters:
1. Figure φ L φ U
A 0,9 ≤ φ L < 1,0 0 ≤ φ U ≤ 0,1
B 0,6 ≤ φ L < 0,9 0,1 ≤ φ U ≤ 0,4
C 0,4 ≤ φ L < 0,6 0,4 ≤ φ U ≤ 0,6
D 0,1 ≤ φ L < 0,4 0,6 ≤ φ U ≤ 0,9
E 0 ≤ φ L < 0,1 0,9 ≤ φ U ≤ 1,0
Now the part light output Ф LT which falls on a standardised task area below the luminaire
must be calculated in relation to Ф L
Ф LT
That means φ LT = ———
Ф L
Herewith a second classification Table 2 is possible:
2. Figure φ LT
0 -
1 0 < φ L ≤ 0,3
2 0,3 < φ L ≤ 0,4
3 0,4 < φ L ≤ 0,5
4 0,5 < φ L ≤ 0,6
5 0,6 < φ L ≤ 0,7
6 0,7 < φ L ≤ 0,8
7 0,8 < φ L ≤ 0,9
8 0,9 < φ L ≤ 1,0
And the part of the light output Ф UC which falls on a standardised ceiling area above the
luminaire must be calculated in relation to Ф U
Ф UC
That means φ UC = ———
Ф U
Herewith a third classification Table 3 is possible:
3. Figure φ UC
0 -
1 0 < φ UC ≤ 0,5
2 0,5 < φ UC ≤ 0,7
3 0,7 < φ UC ≤ 0,9
4 0,9 < φ UC ≤ 1,0
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Light distribution categories
Class Categories:
With “LDC-class” the light distribution characteristic is defined. The SIA-Norm 380/4
summerises the various classes into 10 categories:
Class Distribution Direct light Example
A10-A32 wide 100% Recessed luminaire
A40-A44 medium 100% Recessed luminaire
A50-A80 narrow 100% Recessed luminaire
B21-B22 wide 75% Pendant luminaire
B31-B33 normal 75% Pendant luminaire
B41-B63 narrow 75% Pendant luminaire
C11-C33 wide 50% Pendant luminaire
C42-C63 medium to narrow 50% Pendant luminaire
D11-D63 all 25% Free standing luminaire
E02-E73 very wide 0% Indirect luminaire
The selected LDC-class influences the room utilization factor: as wider the distribution, as
darker the room and as lower the direct part as lower the room utilization factor; this
means that more light has to be installed to reach the required illuminance.
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