the contrast of a luminescent image produced by a crt display device is improved by disposing a variable light transmissivity panel adjacent the crt faceplate to intercept and attenuate ambient light reflected from the screen of the crt . control circuitry is provided to effect a decrease in the transmissivity of the panel in response to increasing ambient light intensity . the circuitry also effects an increase in the electron beam current with increasing ambient light intensity to increase the intensity of the luminescent image produced by the electron beam . when the device is not operating , the panel has a very low transmissivity causing the faceplate to appear dark .