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{Continued from page 23)
And in Column E the variation between 0.69 and 0.80 is 16%.
Now let us see what new goal the present screen brightness committee could set for the industry and whether these aims could possibly be realized with today’s available equipment. Please bear in mind that 30 foot-lamberts is still considered generally as the best level of brightness.
Present projection equipment wdth highspeed condensing lenses, or 16-inch reflectors, and with efficient projector shutters and f/1.9 lenses, can deliver from 10,000 to 11,000 lumens to the screen. Assuming again a maximum theatre screen width of 30 feet, with similar conditions, we can obtain a center screen brightness of 14 footlamberts. This then is our new obtainable minimum brightness level.
Going back to the table, let us check the change in contrast seeing ability between levels of 14 and 30 foot-lamberts. Column B shows zero variation ; Column C shows a variation from 0.41 to 0.50, or 22%; Column D shows a variation from 0.87 to 0.98, or 12%; and Column E shows a variation from 0.80 to 0.94, or 17%. These variations in contrast perceptions are in most cases an improvement over the previous conditions.
RECENT LAMP ADVANCES
Following the same reasoning used in establishing the first set of screen brightness standards, it is apparent that these standards could be changed to considerably higher values. It should be possible to propose a new value of mean brightness of 20 foot-lamberts, with a minimum of 14 foot-lamberts and a maximum of 30 foot-lamberts.
These new and higher limits of screen brightness, which may be reached readily with moderji apparatus, would improve the quality of our projected pictures. Higher densities in positive films could be permitted, thus greatly increasing the ranges of pictorial tones. Furthermore, a higher level of screen surround illumination could be permitted without detracting from the apparent picture brightness, and these conditions would materially increase the visual comfort and appreciation of the spectator.
During the last ten years, projection equipment manufacturers have brought out complete new series of lamphouses, projectors and lenses which can be combined properly to deliver pure white light to theatre screen in quantities ranging from 5000 to 11,000 lumens — sufficient light to produce the screen brightness discussed above for screens of all sizes up to 30 feet. During just the last few years lamps have been developed which make these higher levels with the larger picture sizes obtainable in the efficient, economical reflector lamps.
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MOTION PICTURE HERALD, NOVEMBER 10, 1951