Selection of displays operated harmlessly to human eyes based on their readability

Displays are the key devices for reading data without errors at factories and offices efficiently. In addition, selection of displays is very important to keep the human eyes healthy if displays are contiguously operated for a long time of more than 100 min. Readability is the performance of display defined as the human-machine interface, strongly related to the physical capability of human eyes to correctly read the designated characters without errors within a specified time span on the display. The readability was mathematically defined for evaluating the figure of merit for the static performance of image and video displays. It was successfully utilized for evaluating the image displays. Data of readability for TFT-LCDs were acquired for both white LED matrices and two-row cold cathode fluorescent lamps (CCFLs), each used as backlight. The readability tested for TFT-LCD with white LED matrices showed the higher performance than that for TFT-LCD with two-row CCFLs. The relative efficiency of works for display operations contiguously carried out for a time span of 0 to 90 minutes utilizing TFT-LCD with white LED matrices was higher than that which was obtained utilizing TFT-LCD with two-row CCFLs by a factor of 10 %. Logarithmic readability newly defined here was applied to practical field data, and it was verified to be useful for evaluating the quality of backlight for TFT-LCDs at glance.