Investigation of the effect of ambient lighting on contrast sensitivity using a novel method for conducting visual research on LCDS

Abstract

The DICOM part 14 greyscale standard display function provides one way of harmonising image appearance under different monitor luminance settings. This function is based on ideal observer conditions, where the eye is always adapted to the target luminance and thereby also at peak contrast sensitivity. Clinical workstations are, however, often submitted to variations in ambient light due to a sub-optimal reading room light environment. Also, clinical images are inhomogeneous and low-contrast patterns must be detected even at luminance levels that differ from the eye adaptation level. All deviations from ideal luminance conditions cause the observer to detect patterns with reduced eye sensitivity but the magnitude of this reduction is unclear. A method is presented to display well-defined sinusoidal low-contrast test patterns on an liquid crystal display. The observers were exposed to light from three different areas: (i) the test pattern covering approximately 2 degrees x 2 degrees; (ii) the remaining of the display surface and (iii) ambient light from outside the display area covering most of the observers' field of view. By adjusting the luminance from each of these three areas, the observers' ability to detect low-contrast patterns under sub-optimal viewing conditions was studied. Ambient light from outside the display area has a moderate effect on the contrast threshold, except for the combination of high ambient light and dark objects, where the contrast threshold increased considerably.