What is the difference between sleeping at hours of darkness and sleeping at time and why?

hello i am new on yahoo!answears and i spend my night on the PC...until 4am...and i started wondering what is the difference between sleeping at day and sleeping at dark please answear me as professionally as you can.What is the difference between sleeping at hours of darkness and sleeping at time and why?
This isn't a professionally answer but i know that when it's getting night, your melatonin-production begin. This is the cause of idea sleepy.. So when you sleep at day you are interrupting your biological clock... This could front to depressions and such things..
our clock in our body are programmed to sleep at darkness. sleeping at night is lot quitter than during the afternoon. and of course is dark and it's easier to fall asleep.