Aluminized screen may refer to a type of
cathode ray tube (CRT) for video display, or to a type of
projection screen
A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the w ...
for showing motion pictures or slides, especially in
polarized 3D.
Some cathode ray tubes, e.g., television picture tubes, include a thin layer of
aluminium
Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...
deposited on the back surface of their internal
phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...
screen coating. Light from an excited area of the phosphor which would otherwise wastefully shine back into the tube is instead reflected forward through the phosphor coating, increasing the total visible light output. The aluminium layer must be thick enough to reflect light efficiently, yet not so thick as to absorb too great a proportion of the
electron beam
Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to ele ...
that excites the phosphor.
Some projection screens have an aluminized surface, usually an aluminium paint rather than a solid sheet of the metal. They reflect polarized light without altering its polarization. This is necessary when showing
3D film
3D films are motion pictures made to give an illusion of Three-dimensional space, three-dimensional solidity, usually with the help of Stereoscopy#3D viewers, special glasses worn by viewers. They have existed in some form since 1915, but had been ...
s as left-eye and right-eye views which are superimposed but oppositely polarized (typically at opposite 45 degree angles to the vertical if linearly polarized, right-handed and left-handed if circularly polarized). Audience members wear polarized glasses that allow only the correct image to be seen by each eye.
Cathode ray tube
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