US2260924A

US2260924A - Luminescent screen

Info

Publication number: US2260924A
Application number: US362681A
Authority: US
Inventors: Frank E Swindells
Original assignee: PATTERSON SCREEN Co
Current assignee: PATTERSON SCREEN Co
Priority date: 1940-10-24
Filing date: 1940-10-24
Publication date: 1941-10-28
Anticipated expiration: 1958-10-28

Description

Patented Oct. 28, 1941 Frank E. 'Swindells,

Patterson Screen Company,

Towanda, Pa., assignorto' The .Towanda, Pa., a

corporation of Pennsylvania No Drawing. Application October -24, 1940, Serial No. 362,681

4- Olairns. *(Gl. 250-81) This invention relates to television apparatus and particularly to luminescent viewing screens adapted to be rendered fluorescent by cathode rays and the like.

Many'current methods of television reproduction operate at an image rate of thirty images or frames per second. At the receiving station, images are reproduced on a luminescent screen in television tubes, cathode ray tubes, and the like. It has been determined that television reproduction at the rate of approximately fifteen frames or images per second has many inherent advantages over the thirty frames per second system. The present invention pertains to a luminescent viewing "screen intended for use particularly with fifteen images per second television reproduction apparatus.

It is the object of my invention to provide a luminescent viewing screen for television apparatus which will reproduce images at the rate of fifteen per second without producing the sensation of flicker, as one image replaces another on the viewing screen.

It is the further object of this invention to provide a luminescent screen having substantially white fluorescence, and an after-glow of sub stantially one-fifteenth second duration.

It is another object of this invention to provide a luminescent screen of any desired tint or shade of fluorescence together with the specific extent or duration of after-glow heretofore mentioned.

It is another object of this invention to provide a luminescent screen for fifteen frames per second television which has an after-glow of adequate luminosity for one-fifteenth second duration, the purpose of the said after-glow being to eliminate the sensation of flicker in the reproduction of television motion pictures.

Other objects and advantages of this invention will be readily apparent from the following description of the preferred embodiment of the invention described below.

Heretofore, many different materials have been proposed for fluorescent screens in television and cathode ray tubes. Materials commonly used include zinc sulfide, zinc cadmium sulfide, zinc silicate, zinc beryllium silicate, and others. In the thirty images or frames per second television apparatus utilizing such materials, no objectionable sensation of flicker is apparent. However, the use of such fluorescent materials in the fifteen frames per second system results in a very objectionable sensation of flicker as each image replaces another. I have discovered that a viewing screen having an after-glow characteristic providing luminescence of adequate intensity for approximately one-fifteenth second duration effectively eliminates the sensation of flicker in the fifteen frames per second system. Tests indicate that the usual fluorescent materials provide either too much after-glow resulting in blurred images, or too short or too weak after-glow resulting in objectionable flicker.

My investigations show that cadmium silicate fluorescent material has a desired after-glow of effective luminosity up to one-fifteenth second duration. Such material is preferably manganese-activated, as is well known in the fluorescent material art. However, cadmium silicate has a .red or pink luminescence which is not particularly desirable in television screens. I have found that this material may be mechanically mixed with other fluorescent materials to modify the objectionable pink or red fluorescence characteristic, without seriously impairing the desired after-glow characteristic. For example, tests show that a screen prepared from a mechanical mixture of 55 parts manganese-activated cadmium silicate, 30 parts silver activated zinc sulfide, and 15 parts (manganese-activated) zinc silicate provides substantially white fluorescence and flickerless reproduction of images in fifteen frames per second television apparatus. The after-glow is of adequate luminosity up to onefifteenth second duration, and thereafter negligible or insufficient to cause blurred reproduction.

The proportions of the materials mixed with the cadmium silicate may be varied to produce fluorescence of warm white, cold White, daylight white, or various desired tints and shades. Varying the cadmium silicate in the range of 53 to 61% by weight, the zinc sulfide from 26% to 31% by weight, and/or the zinc silicate from 12.5 to 18% by weight, makes wide variation in the tint or shade of fluorescence of the mixture. As the result of my research, I have found that the after-glow of available cadmium silicate is such that the fluorescent material mixture should contain not substantially less than 50% cadmium silicate, by weight, in order to provide an afterglow of sufiicient intensity to eliminate the sensation of flicker in fifteen frames per second television reproduction. The use of less than 50% cadmium silicate in the fluorescent material mixture is indicated where the available cadmium silicate in smaller quantity provides an afterglow of adequate intensity for one-fifteenth second duration to eliminate the sensation of flicker. Higher percentages of cadmium silicate, i. e.,

as somewhat greater than 61% by weight, provide greater intensity of after-glow, but detract from the whiteness of fluorescence that is usually de sired in television reproduction. Other materials may be added to or substituted for the zinc sulfide and zinc silicate components of the fluorescent material mixture in order to obtain fluorescence of a particular desired tint or shade.

Although I have described and claimed my invention with particular reference to reproduction at the rate of fifteen images per second, it is readily apparent that the desirable advantages of this invention are also obtained at reproduction rates somewhat above and/or below fifteen images per second. Therefore, it is my intent in reciting approximately fifteen images per second, and in reciting an after-glow duration of the order of onefifteenth second, or substantially one-fifteenth second, to include therein those rates either above or below which approximate the figures specified.

What I claim is:

l. A luminescent screen material for use in fifteen images per second television reproduction apparatus comprising a mixture of 55% by weight manganese-activated cadmium silicate, 30% by weight silver-activated zinc sulfide, and 15% by Weight manganese-activated zinc silicate, to provide a screen of substantially white fluorescence having an after-glow of the order of one-fifteenth second duration for eliminating the sensation of flicker as one image replaces another on said screen.

2. In television apparatus for reproducing images at the rate of approximately fifteen per second, a Viewing screen of luminescent material activated by cathode rays, said material comprising manganese-activated cadmium silicate present at least in an amount on the order of fifty per cent by weight, the luminescent material having an after-glow the duration of which is of the order of one-fifteenth second, when activated by the cathode rays, for eliminating the sensation of flicker as one image replaces another.

3. In television apparatus for reproducing images at the rate of approximately fifteen per second, a viewing screen of luminescent material activated by cathode rays, said material comprising manganese-activated cadmium silicate present at least in an amount on the order of fifty per cent by Weight, mixed with other luminescent substances having a color of fluorescence different from that of said cadmium silicate, the luminescent material having an after-glow the duration of which is of the order of one-fifteenth second, when activated by the cathode rays, for eliminating the sensation of flicker as one image replaces another.

4. In television apparatus for reproducing images at the rate of approximately fifteen per second, a viewing screen of luminescent material activated by cathode rays, said material comprising manganese-activated cadmium silicate, silveractivated zinc sulfide and manganese-activated zinc silicate, said cadmium silicate being present at least in an amount on the order of fifty per cent by weight, the luminescent material having an after-glow the duration of which is of the order of one-fifteenth second, when activated by the cathode rays, for eliminating the sensation of flicker as one image replaces another.

FRANK E. SWINDELLS.