The answer to 'lifespan of dimmer switch' is that a typical dimmer switch can last 15-20 years with normal use. Dimmer switches are designed to be long-lasting, but their lifespan can vary depending on factors like frequency of use, quality of the switch, and electrical load.
Higher-quality dimmer switches from reputable brands tend to have a longer lifespan, often 20 years or more. Cheaper or lower-quality dimmers may only last 10-15 years before needing replacement. Proper installation and not exceeding the dimmer's maximum wattage rating can also help extend its useful life.