When installing a darkroom ventilation fan, you also need a corresponding louver to ensure an effective flow of air, but the louver must also prevent light leakage into the darkroom. The solution is an Air-No-Lite Louver. The baffles prevent light leakage while allowing adequate air flow. The L-1212 louver is the correct size for installation with the Doran A-1212 darkroom fan. 13¾"x 13¾"x 1¾" exterior dimensions.