Patent attributes
An edge exposing apparatus includes a photo detector and a lighting time measuring circuit for detecting a decrease in performance of light source units. The lighting time measuring circuit detects a ready state ((stabilization of luminous intensity) of the light source units, for example by measuring a lighting time for a startup (switch-on) of the light source units. When the measuring circuit detects a preset lighting time, or when the photo detector detects a luminous intensity below a preset value, the light source units are determined to have lowered performance, and are switched off. When a decrease in performance of one unit is detected, a replacement light source unit is started while continuing edge exposure with one or more other light source unit(s). When a ready state is detected, the edge exposure with the one light source unit is terminated (switch-off), and edge exposure is performed with the replacement light source unit.
