why is ti easier to study at night?

Maybe 'easier' is not the right word, but why is it that I cannot concentrate during day time, but I can at night time?

Is it because I feel that the day is running away and I am trying to write as much as I can so that I dont feel that the day has gone by unnoticed? 

I am always more inspired at night.. I am more tired, and a bit more relaxed I suppose. 

I get to realize that the day is almost gone, so whatever I do is a bonus..

I really dont know! 

Any psychologists out there to enlighten me?

The Physicist