I usually don't switch off the light in my room as when we designed the office layout, I wanted to have a window which will face my table and lighted up my whole room. As the window is nearly from floor to ceiling, the lights from the window are enough to ensure this.
Here are some pictures of the window with the blind turn down and the room.
Sometimes, I do have to switch on the lights when the day is overcast and there is just not enough natural light to light up my room but I do what I can in keeping the unnecessary lights turn off.
Maybe its a small gesture but at least that's my small contribution for the environment. What's yours?