Retrofit kits are basically all of the hardware you need to be able to use higher wattage compact fluorescent bulbs. The hardware that you have now will only handle 15w bulbs. If you could find higher watt bulbs that would fit into your current setup, it would be a fire hazard as its only rated to handle up to 15w. Retrofit kits replaces the hardware with hardware that will handle higher wattage.
I've personally found it cheaper to get whole new light appliances and glass tops. A lot less hassle, too, for ijits like me who don't have much in the DIY skill arena.
