An easy-to-apply method for determining permissible exposure limit of retina to light

Long exposure to intensive artificial light imposes threats to the retina. It is crucial to know the permissible exposure time to prevent photoretinitis. One complicated quantification method is available, which, however, also requires instrumentally measured spectrum and illuminance. We present herein an easy-to-apply formula and a ready-to-use table derived therefrom to determine the permissible exposure limit for any given desk lamp at any viewing distance. One only needs to acquire its color temperature and luminous flux labeled on the product. The method can be used to assist the general public in quickly assessing the potential hazardous status of their desk lamps, if any, and guide the field experts in designing human-eye-friendly lighting.