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Illuminance Measurements for Lighting Installations
(Extract from JIS C 7612 standards)
For general lighting, the horizontal angle of light shall be measured to
obtain an average value. Unless otherwise specified, the height of the
measuring surface shall be within 85 cm from the floor, 40 cm from the
tatami floor in the case of a Japanese-style room, or nearly on the surface of
the floor or ground in the case of a corridor or the outdoors (If it is difficult
to measure the illuminance on the floor or ground, the height shall be within
15 cm from the floor or ground).
The location for measurement shall be divided into equal areas by vertical
and horizontal partitioning lines, and the average illuminance for each area
shall be calculated. The calculated average of the areas shall be the average
illuminance of the total area measured. According to the 5-point method
given in Figure 14, the middle of each side (the m point) and the center of
gravity (the g point) shall be measured to obtain the average illuminance for
each area according to the following expression:
E
0
= –– (E
m1
+ E
m2
+ E
m3
+ E
m4
+ 2E
g
) = –– (
∑
E
m
+ 2E
g
)
––
1
6
1
6
If the variation of the illuminance is small, the illuminance may be
measured according to the 4-point method given in Figure 15 after
measuring the illuminance (Ei) of the four corners (the i point):
E
0
= –– (E
i
1
+ E
i
2
+ E
i
3
+ E
i
4
) = ––
∑
E
i
––
1
4
1
4
