Accurate UV measurements of spectral irradiance and exposure are essential to optimized design and production control of the UV curing process. Methods of measurement as well as some sources of error are presented. Radiometers and exposure meters are discussed, along with several techniques of using them for process specification and troubleshooting for both medium-pressure and LED systems.
The most important principle of effective radiometry is that the measurements must be relevant to the process or, in other words, must be related to the development of the physical properties of the final product. This is also true of the need for optical characterization (or specification) of UV lamps for the purpose of system design.
Process design determines the exposure requirements of the chemistry to be cured -- such as irradiance profile, spectral distribution, power level, peak-to-energy ratio, temperature, and time (or speed). In addition to aiding in the optimization of the process, radiometric measurements are useful in quantifying the successful exposure parameters, so the process can be reliably duplicated. This is the important step of transferring the process form the lab to production design. The function of radiometry is to provide quantitative information about the critical requirements of the process and to establish the limits or “window” within which the process is successful.