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442 THEATER LIGHTING [J. s. M. p. E.
The same film reviewed at about three times the distance (approximately 72 feet) causes less visual shock and could be classified as almost perceptibly uncomfortable with dark surroundings, and with screen surroundings ten times as bright could be classified as almost comfortable.
Table Showing the Visual Comfort Scale (Holladay] Scale Value Sensation Classification
0 . 3 Scarcely noticeable
0 . 6 Most pleasant
0 . 9 Still pleasant
1 . 2 Limit of pleasure
1 . 5 Very comfortable
1 . 7 vStill comfortable
1 . 8 Less comfortable
1 .9 Boundary between comfort and discomfort 2 . 2 Perceptibly uncomfortable
2.4 Uncomfortable
2.6 Boundary between objectionable and intolerable 2.8 Irritating
Somewhat different conditions exist when film more nearly average in character is projected. Using in this case a screen brightness only one-eighth that for the light film and a viewing distance of 25 feet, the sensation could be classified as comfortable for dark screen surroundings; and the sensation would be at the limit of pleasure, that is, the higher limit of that brightness which is pleasant to view, when the screen surroundings were increased to ten times the brightness or approximately that which would obtain in a theater which had a buff front wall illuminated to about 0.004 foot-candle and surfaces surrounding the screen of about the same illumination and brightness.
From the standpoint of visibility, conditions are best when the screen surroundings are darkest. This condition, however, is the least pleasant from the standpoint of visual comfort. Calculations from data furnished by the same authority indicated, however, that the changes in visibility are very small, within the range of change in screen brightness referred to previously, that is, from black velvet surroundings to materials reflecting about ten times as much light, so that it would appear that visual comfort is the more important factor and that the screen surroundings may be made as bright as is practical from the standpoint of lessened contrasts due to extraneous light reaching the screen.