Spectral output is the intensity of light at each wavelength over the range of wavelengths emitted by the lamp. For the most effective cure, the lamp's pattern of output should be matched to the pattern of absorption of the photoinitiator. Because there are absorption principles common to many systems, an assembler often has a choice of lamps for use in this process. Major absorption areas of importance include 254 nanometers, the wavelength responsible for surface cure. Wavelengths of 400 to 436 nanometers use visible photo-initiators to absorb light.
Intensity is the overall power of the lamp.
Also known as power density, it is most often designated in watts and refers to total lamp output across the entire electromagnetic spectrum. The cure time of the chosen adhesive depends on the intensity and the wavelength of the UV light. Such a system can only be used with adhesive formulations in which a secondary cure mechanism has been incorporated. Secondary mechanisms include heat, moisture and activators. Surface curing is especially important when using UV light.