Product: The Sims 4
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What expansions, game packs, and stuff packs do you have installed? All
Steps: How can we find the bug ourselves? On an empty property, create a room (mine was 14x11 but any size will do). Add ceiling lights to the interior (I placed 8 of The Subtle Saucer Light, evenly spaced around the room). Add windows around the structure (I used Tri-Pane Three Panel windows). Change time of day to night (or play in live mode until it's night time). Observe the light outside on the exterior ground.
What happens when the bug occurs? There is a very large amount of bright light on the ground all around the structure where windows are present. It has a very unnatural look, more like the light is coming from underneath the house as opposed to from the windows. Also, placing curtains or blinds on the windows does not have any sort of dimming effect (which you would expect to see).
What do you expect to see? A reasonable amount of light emanating from windows and affected by the presences or absence of curtains/blinds.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? No
Here is an image showing the issue:
And see here for what a house realistically looks like at night.