The answer to 'why is my generator dimming lights' is that a problem with the generator's voltage regulation or load capacity is likely causing the lights to dim. This can happen when the generator is overloaded or not producing enough power to meet the electrical demand of the lights and other connected appliances.
Some common causes include an old or malfunctioning voltage regulator, a generator that is too small for the electrical load, or issues with the wiring or connections. If the generator is dimming the lights, it's best to have a professional electrician inspect the system to diagnose and fix the underlying problem.