Not just the transformer, but also the lights put out heat. The 'can' lights typically used are abt 20-25w each and the have a metal can to help dissipate the heat. It might be worth your while to make a trip to your local lighting store (or Lowes or HD) and actually feel how warm some of the different lights get. They also have some led products you can check out. What I am saying here is simply that the flex strings were designed for high output and high density (1" spacing) - just what you'd want for xmas lights, maybe not so much for under-the-counter lighting. Take a look at the wiki for comparison. You'll find that a flex string uses 3.96amps (33ma/node) or 47 watts.
