Three-component systems, which contain a light-absorbing species (thiacarbocyanine dye), an electron donor (typically n-butyltriphenylborate salt), and a third component (usually an N-alkoxypyridinium salt or 1,3,5-triazine derivative, respectively), have been applied as the efficient, visible-light-sensitive photoinitiators. The kinetic studies of free radical polymerization reveal a significant increase in polymerization rate with addition of a third component to the photoinitiating system. Although three-component systems have been consistently found to be faster and efficient than their two-component counterparts, these systems are not well understood and a number of distinct mechanisms have been reported in the literature. (c) 2010 Elsevier B.V. All rights reserved.