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 25V voltage. When reverse-biased, the photodiodes should not continually exceed 25V. You need a breakdown voltage of 15V to make sure photodiodes work. There is 35nA current flowing through a photodiode even in the absence of light input.