Cationic Photoinitiators react very differently to the previous mentioned Type I, Type II Photoinitiators. Mainly iodonium and sulfonium salts are employed as cationic photoinitiators. When irradiating these salts with UV-light they undergo, like Type I photoinitiators, homolytic bondage cleavage. The formed radicals react with a proton donor to a Brønsted or Lewis acid. The generated acid then initiates the polymerization.