The answer to 'why is my light fixture dimming lights' is that there are several common causes, including a faulty dimmer switch, loose connections, aging wiring, or a problem with the light fixture itself. Symptoms may include the lights flickering, dimming, or not turning on at all.
If the lights are dimming, the first thing to check is the dimmer switch. Over time, dimmer switches can wear out and fail, causing the lights to dim. You can try replacing the dimmer switch with a new one. If that doesn't fix the issue, it could be a problem with the wiring or the light fixture. Loose connections in the electrical box or issues with the fixture's internal components can also cause dimming lights. In some cases, old or damaged wiring may need to be repaired or replaced by a professional electrician.