The answer to 'why is my switch dimming lights' is that a faulty or improperly installed light switch is the most common cause. This can happen when the switch wears out over time, the wiring connections become loose, or the switch is not compatible with the lighting load. Symptoms include the lights flickering, dimming, or turning on and off intermittently.
To fix this, you'll first want to inspect the switch and wiring for any obvious issues like loose connections or damaged components. If everything looks okay, you may need to replace the switch. This is usually a simple DIY repair, but if you're not comfortable working with electrical systems, it's best to call a licensed electrician to diagnose and resolve the problem safely.