We have all had that one exterior image that showed a room inside the building, usually that specific room is much darker than expected, as per image below.
You could simply adjust the sun's brightness, but that would cause the rest of the image to "burn out" or you could run it through Photoshop but that is an extra process and a waste of time.
Using this tool is easy, it allows you to stretch it to any opening size. Just remember when you are ready to render, slide the lights slider to "by Settings"
This will enable your "artificial lights" without having to go to each individual light.
In the image below we can see an improvement in the dark areas.