plants leaves dropping

why do my plants leaves drop like crazy during darkness? is this bad or regular?

This is regular to a extent. Alot of times leaves will turn brown or yellow and drop off the plant because they are no longer needed and completed their purpose. It just depends on the overall health of the plant though if it becomes a problem. But must of the time its just normal and fine. I have it happen on a daily basis with how many plants I have and just clean them up. Appears to be most of the leaves that dont have light contact anymore that are the ones that fall off

regular ......