Every corner and space within the room should be visible to the teacher. Keep in mind that the physical environment effectively forms the foundation for good behavior on the part of the students. For example, in an early education classroom, the block center is far away from the Lego center so the set-ups don't get knocked down accidentally and cause problems. Biological concerns are important too. Children's eyes, particularly in the early primary grades, are not as well developed as adult eyes.
Full lighting increases stimulation for some children.
Lower lighting is more relaxing and easier on the eyes. I always keep them on on-third power. If this is a viable option, notice how quiet the room becomes when you lower the lights. I firmly believe that children want to behave, and when learning is fun and enjoyable, they will. With this as a philosphical basis, it is necessary to create a positive environment.