Complex sentence: One of the advantages of photo-curing is that it can be done selectively using high energy light sources, for example lasers, however, most systems are not readily activated by light, and in this case a photoinitiator is required.
Split into simpler sentences: One of the advantages of photo-curing is that it can be done selectively using high energy light sources, for example lasers. Most systems are not readily activated by light, and in this case a photoinitiator is required.