Under each cabinet there is a place where the electrical wire comes out of the wall and connects to the lighting fixture.
Replacing under cabinet fluorescent lighting with led.
One way to do replace the current lights with led lights and keep the same on off switch is to put a 24v transformer at the point where the current 120v wire comes out of the wall for each cabinet but that is six.
Types of under cabinet lighting bar and strip lights bar and strip styles of under cabinet lighting started with fluorescent lamp fixtures designed for under cabinet use.