|If you are inside; why is it brighter on the south or southwest side of the house?|
|The sun "rises" in the east and moves toward the west during the day until it sets. The south and west are in direct sun at the hottest parts of the day when the sun is most intense.
The sun is not directly overhead. In winter, the angle is especially noticeable because the sun is "lower" in the sky.
I hope this helps.