The OP535A is a Silicon NPN Photodarlington moulded in a green plastic package. The narrow receiving angle provides excellent on-axis coupling. This device is 1 00% production tested using infrared light for close correlation with Optek GaAs and GaAIAs emitters. Photodarlington device is normally used in applications where light signal levels are low and more current gain is needed than is possible with phototransistors.