Guide to UV Measurement
Irradiance
Irradiance is the radiant power within a stated wavelength range arriving at a surface per unit area, usually expressed in watts or milliwatts per square centimeter. Irradiance varies with lamp output power, efficiency and focus of its reflector system, and distance to the surface. It is a characteristic of a lamp’s geometry and power so UV irradiance does not vary with speed. The intense peak of focused power directly under a lamp is referred to as peak irradiance. Irradiance incorporates all of the individual effects of electrical power, efficiency, radiant output, reflectance, focus, bulb size, and lamp geometry.
Irradiance data must always include identification of the wavelength range to which it applies. This is one of the most common omissions in radiometry. When irradiance is measured in any specific range of wavelengths, it is called "effective irradiance." When this wavelength range is clearly understood, the term irradiance is sufficient. Intensity is not a technically defined term, but is commonly but improperly used to mean irradiance. Peak irradiance has a distinct effect and benefit on speed and depth of cure. Irradiance levels in 3-D curing are typically much lower than in flat linear curing.