IM 51011-01EN
51
20. Characteristic of Oblique Incident Light
When reading a book at night, the brightness differs between
reading under a light and reading a little farther from the light.
In such a case, you probably noticed that the book was easier to
read when you faced the book toward the light.
If the angle between the incident light and the line perpendicular
to the illuminated surface is defined to be θ, the illuminance of
the surface is proportional to cos θ.
This characteristic is standardized.
If the lux meter does not meet the standard, illuminance of
oblique incident light cannot be measured accurately.
The following figure shows the characteristic of oblique
incident light.
–80 –70 –60 –50 –40 –30 –20 –10
0 10 20
80
70
60
50
40
30
Angle of oblique incidence (°)
(%)
–30
–20
–10
0
10
20
Tolerance for Class AA
30
Relative illu
minance
Summary of Contents for 51011
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