The answer to your question is a slightly complex one because the physics of light are complex. Light is measured in two values: wavelength (measured in nanometers or “nm”) and intensity (emitance measured in milliwatts per square centimeter “mW/cm²”). LED lights are not the same wavelength as UV CFL (compact fluorescent lamps). UV CFL lamps emit low intensity light in the wavelength range from 345 nm into the visible spectrum (400 nm to 850 nm). The low intensity of the UVA spectrum (320 nm to 400 nm) results in a very low probability of damage to the skin of the back of the hand. The intensity of the LED curing lamps is not in the UVA wavelengths because nearly all of the LED curing lights on the market in our industry are 405 nm (violet spectrum), which is very near the top end of the UVA spectrum and emit at a higher intensity. This wavelength is less damaging to the skin because the violet spectrum does not cause skin damage.
We should always remember that our bodies are designed to be exposed to varying wavelengths of light, including UVA and some low levels of UVB light. Our body is also designed to repair itself upon overexposure conditions. It is equally important to understand that as in every other aspect of our lives, we should always use the equipment we have at work and at home in the manner it was designed to be used.
Ultimately, both light sources as they are used in the industry are not damaging to the skin. Each light source is considered safe to use as directed by the lamp and gel manufacturers. Each light source has been found via independent testing to not be a source of skin cancer when the lamps are used as instructed by the manufacturers.
— Jim McConnell, president, Light Elegance (www.lightelegance.com)