Constancy of built-in luminance meter measurements in diagnostic displays

Liquid crystal displays used to interpret medical images are often equipped with built-in luminance meters to evaluate luminance response and Grayscale Standard Display Function conformance. This work evaluates agreement between luminance reported by the built-in meters and external measurements.

The white level luminance was measured using a built-in meter and an external meter for 93 primary review workstations (Models MFGD 3420 and MDCG 3120-CB) with between 117 and 49,336 backlight hours (BLH). Measured luminance values were compared via t-test for displays with less than 25,000 BLH and those with more than 25,000 BLH. Bias between meters was also evaluated. Changes in luminance uniformity with increasing backlight hours were explored by determining the maximum luminance deviation (MLD) for subsets of these displays with less than 800 BLH and greater than 35,000 BLH.

The mean difference between built-in and external luminance measurements was 5.84% and 38.92% for displays with less than 25,000 and greater than 25,000 BLH, respectively, with a statistically significant difference in the means (p < 0.001). For displays with low BLH, a statistically significant bias was observed (p < 0.001) between built-in and external measurements. A high degree of correlation was observed between measurements made with two separate external meters (r = 0.999). The mean MLD was 9.5% and 11.2% for MDCG 3120-CB displays with less than 800 and greater than 35,000 BLH, respectively. The difference in the mean values was not statistically significant (p < 0.001).

Disagreement between the white level luminance measured using the built-in and external meter increased with BLH. Consequently, reliance on values reported by the built-in luminance meter may result in a reduction in image contrast with time. Recommendations have been proposed regarding luminance response testing and corrective action for failing displays.