I have a situation that is puzzling. In my basement, I noticed that the laundry room light is dim when I turn on the lights of the main room. Here is the scenario.

1. Laundry Switch OFF and Basement Switch OFF - Both Lights OFF
2. Laundry Switch OFF and Basement Switch ON - Laundry Light DIM and Baseline Light ON
3. Laundry Switch ON and Basement Switch ON - Laundry Light OFF and Basement Light OFF
4. Laundry Switch ON and Basement Switch OFF - Laundry Light OFF and Basement Light OFF

Everything was fine for years. I did replace 1 of 2 ceiling light fixtures in the basement in September, but this is just occurring now. Also, when I remove the light bulb from the fixture in the laundry room, the lights in the basement do not work regardless of the position of the switch.

Sounds like a loose shared neutral of a 3 wire circuit. Check if these affected circuits use one neutral of a 3 wire cable at the panel. If so check the entire circuit for a loose connection or a splice on the white wire.