This study demonstrates that LEDs do not cure faster or deeper than halogen light curing units. If the composites contain beside camphorquinone additional co-initiators the depth of cure obtained with halogen is statistically significantly greater than LED technology.

Uhl A. et al. Photo-initiator dependent composite depth of cure and Knoop hardness with halogen and LED light curing units. Biomaterials 2003;24:1787 - 1795

CRA "demonstrates that light intensity & speed of cure do not produce deleterious effects that could be detected clinically".

CRA newsletter March 2002, www.cranews.com

The authors measured lower depths of cure for some composites containing co-initiators when polymerised with LEDs.

"The assembly of the absorption spectra (extinction) and the emission spectra, respectively, shows that the co-initiator Lucirin TPO and co-initiators of Solitaire2 (< 410 nm) cannot be excited by the light emitted from the blue LEDs."

Uhl A. et al. Knoop Hardness Depth Profiles and Compressive Strength of Selected Dental Composites Polymerized with Halogen and LED Light Curing Technologies J Biomed Mater Res (Appl Biomater) 2002; 63: 729 738

Yoon approved in this study that

"When the same light energy was irradiated, DC [degree of conversion] by plasma arc and LED was not significantly different from the halogen lamp."

"... the degree of conversion in only weakly sensitive to wavelength ..."

"... the light intensity within this range is more important than the peak wavelength."

Yoon T.-H. et al. Degree of polymerisation of resin composites by different light sources. Journal of Oral Rehabilitation 2002; 29: 1165 - 1173

"The post-curing effect cannot compensate for the lower hardness of composites containing co-initiators if polymerized with an LED LCU instead of a halogen LCU."

Alexander Uhl, Christian Michaelis et al. The influence of storage and indenter load on the Knoop hardness of dental composites polymerized with LED and halogen technologies. Dental Materials 2004; 20: 21 - 28