THE reflection characteristics
which are desirable in order that the projection screen shall be adapted to an auditorium of given dimensions are pointed out. The distribution of reflected light should be such that for no angle of observation is the brightness greater than four times that at any other angle of observation in the theatre.
Non-uniformity of screen brightness for an observer from a single point is due to difference in angle of observation of the right and left-hand edges of the screen. Since this angular difference is a maximum for observers on a line perpendicular to one side of the screen, the effect is just as serious for a narrow house as for a wide one. A criterion for this nonuniformity tolerance is the brightness ratio of o" to 40" observation.
It is suggested that this ratio ought not exceed ten. Data showing the distribution of reflected light for normal incidence and o" to 50" observation are presented.
Most of the projection screens manufactured at present are included in the forty surfaces that were measured. ?? Communicated by the Director. 'Communication No. zg5 from the Research Laboratories of the Eastman Kodak Company and published in Trans.