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Glossary of Technical Terms 57
Phot — A metric unit of illumination. It equals one lumen per square centimeter.
Photo-electric cell — A cell consisting of a photo-sensitive surface as the negative electrode and a positive electrode between which electrons will flow when the sensitive surface is illuminated.
Photo-electric effect — The emmission of electrons resulting from the action of light.
Photo-electric sensitive surface — A surface which emits electrons under the influence of radiation of certain frequencies. The threshold or minimum value of the frequency necessary to produce photo electrons depends on the composition and the nature of the surface.
Photographic Efficiency of an Illuminant — The ratio of the photographic or actinic flux to the radiant flux.
Photometry — The measurement of light.
Photoplay — A story in motion pictures.
Photo-sensitive surface — Any surface which responds to radiation.
Picture Cycle — The entire series of mechanical operations which takes place between the positioning of one frame of a motion picture film and the positioning of the next frame.
Positive — The developed film, after being printed from a negative.
Pre-release — A picture not yet released for general public showing.
Print — The developed film, after being printed from a negative.
Producer — The maker of motion pictures.
Program — The complete show for a single audience.
Projectionist — A person skilled in the art of projecting motion pictures.
Projection distance — The distance between the projection lens and the surface upon which the image is focused.
Projection lens — The objective which forms upon the screen an image of the lantern slide, film, or other object under examination.
Projection Periods— The total fraction of the picture cycle during which the picture is being projected.
Projection Room — A room or enclosure from which motion pictures are projected.
Props — Contraction of properties. Objects used as accessories in a play.