Radiologists should read images on handheld devices in environments with illumination that is less than 1,000 lx, according to a study published in the October issue of the Journal of Digital Imaging.

To ensure consistent, high-quality display performance in varying environments, Peter Liu, of the University of Maryland, and colleagues designed a study to examine how ambient illumination levels affect visual task performance on handheld displays.

Using DENOTE, a methodology based on noise-embedded text detection, the researchers tested devices and user performance in several illumination conditions ranging from 0.01-31,633 lx. Three male subjects, ages 18-25, were each given the task of detecting and distinguishing four alphanumeric characters embedded in white noise background on two current-generation smartphones. Observer experiments occurred in super bright, medium bright, average, medium dark and super dark illumination conditions. 

The reflectance of the display devices was separately characterized by specular and diffuse scattering. Statistical analysis of gathered data illustrated that user performance generally deteriorated as ambient illumination increased from dark to bright. The best detection performance, therefore, was found in dark conditions. Researchers discovered a negative correlation between illuminance and user performance, with screen reflectance being highly dependent on display technology.

“Handheld display devices for medical imaging exhibit characteristics that may in some circumstances significantly affect image quality. Users must be aware of the limitations when the screen is viewed under different ambient illuminations,” wrote Liu and colleagues.