The bulbs in all fly lights, including the Gardner GT 220 Aluminum Fly Light Trap, are replaceable as they are just like any other bulb in your home. When it blows out or is no longer providing you with the light/function you need, you would replace it with a new bulb. We are getting our catalog team to set up the 20 watt replacement bulbs for the unit in our inventory system and it will be linked on the product page once they are available for ordering.