Would you rather be locked 24/7 in a pitch-black cell or an unbearably bright cell?

Both cells are about the size of your average living room. You have access to a simple bed, a toilet and sink, and are fed twice a day. For the sake of simplicity we'll assume you don't need to shower. You don't get any entertainment or human contact.
The dark cell has no lights and is incredibly dark. The bright cell is lit at all times of day, and is just bright enough to make it uncomfortable and hard to sleep.
Which cell would you pick to be locked inside for an unspecified period of time? Let's say a year.


Source.