Curing lights provide light energy of an emission spectrum. Photo-initiators absorb this light energy and initiate chemical reactions to polymerize a composite material. This process is called photo-polymerization. Both light intensity – or irradiance – and the dental application should factor into a dentist’s decision regarding his or her choice of dental curing light. For instance, irradiance is measured by calculating power output, or milliwatts (mW), of a curing light across the surface area of the curing light guide. A curing light must deliver a minimum irradiance of 400mW/cm2 for a time interval to adequately polymerize a 1.5-2mm thick resin composite.

Clinicians also should consider the clinical application at hand. It has been documented that irradiance of curing lights attenuate/decrease significantly when it passes through restorative materials, such as ceramic restorations or resin composites. The percentage of decrease in irradiance depends on filler type, filler loading, shades, refractive index, opacity, translucency and thickness of restorative materials. Curing lights with high irradiance compensate for the decrease in the loss of total energy and allow dentists to cure resin composites completely. In general, an irradiance of 1000mW/cm2 or higher is considered ideal to cure resin-based materials through indirect restorations.

There have been significant improvements in the curing light technology in recent years. Today, dental manufacturers can develops variety of curing lights, from plasma arc to argon laser curing lights. That said, two curing lights commonly used in the dental operatory are Quartz Tungsten Halogen (QTH) lights and Light-emitting diode (LED) lights.

Quartz Tungsten Halogen (QTH) lights. These lights have a quartz bulb with a tungsten filament that irradiate both UV and white light, which must be filtered to remove heat and all wavelengths except those in the violet-blue range. The lights have broad emission spectrum of approximately 390 nm to 500 nm, which is capable of curing all composites.

Light Emitting Diode (LED) curing lights. These curing lights use light-emitting diodes (LEDs) as a light source and do not require filters. The original LED lights had narrow emission spectrum and low power intensities, necessitating long curing times. This issue was overcome by 2nd generation curing lights with high power intensity. However, they maintained narrow emission spectrum, which restricted them to activate only camphorquinone, and thus could not fully polymerize some composite materials. Third generation curing lights feature broad emission spectrum (380nm to 515nm), along with high irradiance in the range of 1000mW/cm2 and higher, reportedly allowing these lights to light-cure all composites without restriction.