Having recently gone through the process of finding a replacement bulf for my 26 1K "S" model.

It is my understanding that the newer 1KS model is noticeably faster, however the cost difference in bulbs is several hundred $$. As I recall about $50.00 versus $242.00 for the newer Metal Halide bulb which I got from Atlantic Bulb Company, BTW they graciously took back the first bulb I purchased for the 26 1K model.