Pathologists light level preferences using the microscope -- a study to guide digital pathology display use

There is a paucity of guidelines relating to displays in digital pathology making procurement decisions, and display configuration challenging. Experience suggests pathologists have personal preferences for brightness when using a microscope which we hypothesised could be used as a predictor for display setup. We conducted an online survey across 6 NHS hospitals to capture brightness adjustment habits on both microscopes and screens. A subsample of respondents took part in a practical task to determine microscope brightness and display luminance preferences. The survey indicates 81% of respondents adjust the brightness on their microscope, compared with 11% adjusting their digital display. Display adjustments are more likely for visual comfort and ambient light compensation rather than for tissue factors, common for microscope adjustments. Twenty consultants took part in the practical brightness assessment. Light preferences on the microscope showed no correlation with screen preferences, except where a pathologist has a markedly brighter microscope preference. All of the preferences in this cohort were for a display luminance of less than 500cd/m$^2$, with 90% preferring 350cd/m$^2$ or less. There was no correlation between these preferences and the ambient lighting in the room. We conclude that microscope preferences can only be used to predict screen luminance requirements where the microscope is being used at very high brightness levels. A display capable of a brightness of 500cd/m$^2$ should be suitable for almost all pathologists with 300cd/m$^2$ suitable for the majority. The ability to adjust display luminance was felt to be important by the majority of respondents. Further work needs to be undertaken to establish the relationship between diagnostic performance, preferences and ambient lighting levels.