Depriving your cat from natural light is the worst thing you can do!
Cats like to feel warm and secure before they fall to sleep. They also use the sunlight to help make up the slight drop in body temperature that happens once they fall asleep. Some cats will change their sleep positions to follow the movement of the sun, even if it's only coming through the window.
Keeping the cat in a room without any natural light will make him psychologically anguished- Have you noticed cats are active during the night and can sleep for long hours during the day? It's because cats are crepuscular, which means they prefer to be awake at dawn and dusk. As such they would need to be able to sense the changes in the light (day vs night).
Cats are natural hunters, they will keep themselves busy and entertained if they can see out the window, even if the view is not as appealing to a human, they will find fascinating things out and their lives will be happy and complete.
Leave the blinds open a little, your cat will appreciate it.