IM 51011-01EN
53
4-point method
The 4-point method is used when the variation in the illuminance
is small. The four corners (the
i
points) shall be measured to
obtain illuminance Ei, and then the average illuminance for each
area shall be determined according to the following expression:
E
0
= (Ei
1
+Ei
2
+Ei
3
+Ei
4
)= ∑Ei
1
4
1
4
i2
i3
i4
i1
If you use Model 51021, measurements using the 4-point and
5-point methods are easy.
(See chapter 7, “Average Illuminance.”)
There is another method in which the average illuminance of
multiple partitioned areas can be determined directly.
For details, see JIS C 7612.
Summary of Contents for 51011
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