Influence of room lighting on grey-scale perception with a CRT-and a TFT monitor display.

OBJECTIVES To determine the influence of ambient lighting on grey-scale perception using a cathode-ray tube (CRT) and a thin film transistor (TFT) computer display. METHODS A cathode ray tube (Nokia XS 446) and a liquid crystal display (Panasonic LC 50S) were used at reduced room lighting (70 lux) and under conditions recommended for a dental operatory (1000 lux). Twenty-seven observers examined twice a modified SMPTE test pattern [0 to 255; 255 to 0] grey-scale values. The corresponding contrast differences were allocated to four ranges of grey levels (I: 0-63; II: 64-127; III: 128-191; IV: 192-255). The influences of monitor type, grey-scale range and illumination were evaluated by means of repeated measures analysis of variance. RESULTS Detection of differences in monochromatic intensity was significantly earlier with reduced lighting (P<0.0001). When full ambient lighting was used, the TFT display was superior compared to the CRT monitor in ranges II and III (P<0.0001), whereas no differences could be detected for grey intensities between 0 and 63 (P=0.71) and between 192 and 255 (P=0.36). CONCLUSIONS Background lighting hampers grey-scale perception on computer displays. In this study of one TFT and one CRT monitor, the TFT in full ambient lighting was associated with earlier detection of grey scale differences than CRT.

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