Photodiodes are enclosed in Bulk to prevent damage. Photodiodes are packaged in Chip with 30 Gauge PVC Wire packages in order to ensure their safety. Continuous reverse-bias means the photodiodes can withstand only 75V voltage. When reverse-biased, the photodiodes should not continually exceed 75V. You need a breakdown voltage of 50V to make sure photodiodes work. There is 350nA current flowing through a photodiode even in the absence of light input.