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150
RICHARDSON'S BLUEBOOK OF PROJECTION
photometric measurements of reflected light can be made. For the convenience of Bluebook readers the engineering department of the Eastman Kodak Company made a series of test measurements of the reflection and diffusion powers of certain well known surfaces which are tabulated below.
(23) In the accompanying tabulation each surface is given a designating letter, as follows: A — Magnesium, a chalk-like substance the reflection power of which was taken as a standard because of its high reflection value and uniform distribution powers. Its 0 degree angle of reflection power was arbitrarily assumed to be 100 for purposes of comparison with other surfaces. B — Fine grade cotton sheeting. C — Two coats of white paint on cardboard. D — Smooth calendered cardboard. E — Kalsomine on plastered wall. F — Wallboard painted two coats of aluminum paint.
TABLE NO. 6.
(Angles of light measuring instrument to screen surface when measurements were made.)
Average 99 59 76 95 81.5 73 96
0 deg.
5 deg.
10 deg.
20 deg.
30 deg.
40 deg.
50 deg.
100
100
99
98
98
98
97
61
61
60
59
58
57
56
80
79
78
77
76
74
70
.113
109
106
94
83
80
79
82
82
82
81
81
81
81
132
125
115
88
66
50
37
163
150
134
93
61
43
31
The column of averages was arrived at by adding the reflections at all measured angles together and dividing by seven, the number of angles, which is only approximately correct but serves our purpose.
The variations are entirely due to differences in reflection characteristics of the various surfaces and difference in direction in which the light is reflected.
(24) Evidently surface A gives a good and very even screen brilliancy to people seated in all parts of a wide theatre auditorium, since the light is evenly reflected in all directions. There is no visible fadeaway. This sur