Experimental measurements of glare in cathode-ray tubes

Multiple light reflections in the emissive structure and electron backscattering processes, in the vacuum of cathode- ray tubes (CRT) are sources of luminance spread and loss of image quality. To perform glare measurements in CRTs, a detector that can record low intensity signals from small dark fields in the presence of a bright surrounding field is required. We have designed and constructed a luminance probe consisting of a cone-shaped nose and an internally baffled barrel that measures light generated in a spot of abut 4 mm diameter. The probe minimizes light scattering from the probe back into the faceplate, and minimizes contributions from bright surrounding regions. In this paper, we report results on the performance of the probe and demonstrate its application for characterizing CRT devices. The probe is shown to be capable of measuring contrast ratios of at least 800 for dark fields with a radius of 2 cm. Measurements on a medical imaging CRTs illustrate how significant veiling glare in the device can result is contrast ratios of about 100 and how the reflection of ambient light can reduce the contrast ratio to below 25.