Shadow mask color crt with enhanced resolution and/or brightness

Abstract

A color CRT has stripes of different color light emission phosphors (r, g and b) deposited on a faceplate of the tube with the relative widths of the stripes being inversely proportional to the light emission efficiency of the phosphors. By this means the integrated brightness of the emitted light from the different phosphor stripes is the same for the same value beam current. By using a novel double shadow mask arrangement, the widths of the beams from the three guns can be made to match, or substantially to match, the widths of the phosphor elements on which they land. Specifically, the beam from one gun is aligned with apertures through both masks in order to transmit a relatively wide portion of the beam onto the least efficient, phosphor. The portion of the beams transmitted by the first mask for the other two guns are further clipped by the relatively off-set apertures in the second mask. This arrangement enables the advantage of the balanced color output from the screen to be enjoyed without loss of purity margin and provides a significant increase in brightness for a given beam current and/or resolution of the screen. The invention is applicable to CRTs employing shadow masks with slots and phosphor stripes, or holes and phosphor dots and also for CRTs driven in raster scan or vector mode.