ACCO2 - I have seen the collars with LED light built right into the collars at different pet stores. However, I have never liked the quality of them, plus they aren't as bright. That and they are much more expensive then this LED strap designed for cyclists. I much rather use two pieces of quality gear for differing jobs rather than one that does a mediocre try at two jobs.
The Planet Bike BRT LED strap light was only $8.50CDN (before taxes) for me. There is an elastic strap on one end with the quick release buckles that will allow me to adjust the overall length to quite a wide ranges. I could get it around my neck very comfortably and I wear a size 15 collar shirt so it should fit most dogs.