Purpose: To clinically examine the effect of the type of ight-curing unit on the light intensity output and to assess different operator variables which affect light curing of photo-initiated restorative dental materials, in Damascus, Syria. Materials and Methods: A total of 185 private dental practices in the Damascus area were visited to invite the clinicians to participate in this study. The intensity of 163 light-curing units (LCUs) was assessed by radiometry in a standard protocol. The age of the curing unit, light tip direction, distance from restoration surface, time of exposure and the presence of adherent composite remnants on the tip of the light pipe were assessed. Independent samples t-tests and ANOVA with Bonferroni post-hoc tests were conducted (p = 0.05). Results: The light intensity was affected significantly by the type of the LCU (p < 0.001). The increased age of light-curing units significantly reduced the emitted light intensity in LED and QTH units (p < 0.05). The presence of adherent resin composite remnants on the pipe tip of the curing unit was monitored in 74 cases out of 163 (45%). The disinfection wipe was the most common method used to ensure infection control of the curing units. Conclusion: LED units exhibited a significantly better light intensity output at the tip when compared to the QTH units. It is important for dentists to consider all practical aspects which can influence the efficacy of LCUs in daily practice. Schlagwörter: halogen, LED, light-curing unit, light-emitting diode, light intensity, photocuring