Answer:
B. The time of day.
Explanation:
The time of day is not a factor in the illuminance at a center point in a room, because there's no windows.
A really important factor about illuminance is windows, because they allow sunlight to pass through and reach the room. Actually, big windows are mostly preferred because that way people can spend less electricity. So, if we have no windows, it's no important to consider them as a factor in the illuminance of a room.
