Do you mean they are dim?
Just the bedroom lights, others are OK?
Single light fixture or multiple fixtures?
LED or incandescent?
Is this a new problem or has it been going on for some time? Worse over time?
On battery, shore power, or both?
Assuming it is dimming, only on the bedroom lights, I would first check the covers to make sure they haven't faded or otherwise deteriorated to block the light. If the actual bulbs/LEDs are dim and other fixtures throughout the coach are working OK, I would check the voltage at the fixture, the fuse, and the battery. It should be the same, between 12-14 volts, at each location. If not, then there's more troubleshooting to do. If the voltage is OK, I would try replacing the bulbs if they are replaceable (many LEDs aren't). If the voltage is low at the light fixture, you probably have something overloading that circuit. I would look for other 12VDC items that could be on that circuit and make sure they are off/disconnected to see if that fixes the problem.
Current RV Information: 2018 Forrest River Salem Hemisphere 282RK
Previous RVs: 2004 Fleetwood Bounder 32W; 1999 Four Winds Five Thousand 21RB; 1986 Allegro Bay 27'