Ambient light filter

Claim 1

THE COMBINATION OF A CATHODE RAY TUBE AND AN AMBIENT LIGHT TRAPPING FILTER THEREFOR; SAID TUBE HAVING A FRONT WALL INCLUDING AN IMAGE SCREEN OF DIFFUSELY REFLECTING LUMINESCENT MATERIAL DEPENDING ON LIGHT-INTENSITY CONTRAST FOR EASE IN VIEWING THEREOF; SAID FILTER BEING MOUNTED IN FROM OF AND IN PROXIMITY TO THE FRONT WALL OF SAID TUBE AND ARRANGED TO PREVENT IMPINGEMENT OF REFLECTION-PRODUCING LIGHT RAYS ON SAID WALL FROM DIRECTIONS OTHER THAN THOSE WITHIN THE DESIRED VIEWING ANGLE; SAID FILTER COMPRISING A THIN, LATERALLY EXTENSIVE PANEL OF TRANSPARENT MATERIAL BEARING A PLURALITY OF FILTER ELEMENTS; EACH OF SAID FILTER ELEMENTS COMPRISING A GENERALLY PLANAR TIER OF ALTERNATING LOCI OF TRANSPARENT AND HIGHLY LIGHT ABSORBING MATERIAL ARRANGED TO PROVIDE A MULTIPLICITY OF LIGHT TRANSMITTING APERTURES IN CLOSE PROXIMITY TO EACH OTHER AND SEPARATED BY LIGHT ABSORBING MATERIAL TO FROM A GRID PATTERN; SAID TIERS BEING SEPARATED FROM EACH OTHER IN A DIRECTION NORMAL TO THEIR GENERAL PLANES, AND SAID APERTURES IN THE SUCCESSIVE TIERS BEING ARRANGED WITH RESPECT TO EACH OTHER TO PRESENT A MULTIPLICITY OF LIGHT TRANSMITTING VIEWING CELLS EXTENDING DEPTHWISE OF THE PANEL; THE LIGHT ABSORBING MATERIAL ADJACENT EACH VIEWING CELL SERVING TO INTERCEPT AT A NEARLY NORMAL ANGLE AND ABSORB THE ENERGY OF THE AMBIENT LIGHT RAYS ANGULARLY ENTERING SAID CELLS; THE LATERAL DIMENSIONS OF THE APERTURES AND LIGHT ABSORBING MATERIAL IN AT LEAST ONE DIRECTION BEING SO SMALL THAT THE GRID PATTERN IS SUBSTANTIALLY UNRESOLVABLE AT NORMAL VIEWING DISTANCE; THE WIDTH OF THE APERTURES BEING SEVERAL TIMES THE WIDTH OF THE LIGHT ABSORBING MATERIAL BETWEEN APERTURES TO OBTAIN MAXIMUM LIGHT TRANSMISSION FROM THE IMAGE SCREEN; AND MARGINAL MEANS TO PREVENT ENTRY TO LATERAL AMBIENT LIGHT RAYS BETWEEN THE MARGIN OF SAID PANEL AND THE FRONT WALL OF SAID CATHOD RAY TUBE; THE OUTERMOST TIER COMPRISING LINES OF INTENSE BLACK MATERIAL HAVING A LIGHT ABSORPTION FACTOR APPROACHING THAT OF A BLACK BODY RADIATOR; AND THE INNER TIERS COMPRISING LINES OF DENSE TRANSPARENT RED MATERIAL TO PROVIDE HIGH VISIBILITY IN DAYTIME VIEWING CONDITIONS AND TO PRODUCE DARK RED SIGNAL IMAGES FOR GOOD VISIBILITY IN DARK-ADAPTED NIGHT VIEWING CONDITIONS.