The study on light curing technology has been made great progress with widespread use of light- cured composite resins. Because of its inherent drawbacks, conventional halogen light has a limited development. This article introduced the basic principle, characteristics and development of the new light- emitting- diodes（LED） light curing unit, and analyzed the physical, mechanical and biological properties of composite resins cured by the light compared with halogen light, as well as posed the problems which should be solved urgently. The paper provided some theory for the clinical application of the LED light curing unit.
