The answer to 'why is my ceiling fan dimming lights' is that a faulty or incompatible ceiling fan light kit can cause the lights to dim. This is often due to a mismatch between the fan's electrical components and the light bulbs being used.
Common causes include using the wrong type or wattage of light bulbs, a faulty light kit or dimmer switch, or issues with the fan's electrical wiring. Symptoms may include flickering, pulsing, or dimming of the lights when the fan is running.