Guide to UV Measurement
Bulb
A bulb is the final element of the UV source. Bulbs vary dramatically in size, shape, and most important to the UV process, spectral energy distribution. The function of a bulb is to contain the mixture of mercury (or in some cases, xenon), buffer gas, and any additives used to generate a stable spectral output. A bulb also must have the right operating “characteristics” for optimal use with a given power supply. A bulb for an arc lamp system will have characteristic electrodes at the ends while a bulb that uses microwave energy to generate the emission will typically be a sealed quartz tube with no metallic connectors or electrodes. Because of this difference, microwave-driven bulbs are often referred to as electrodeless bulbs. The requirements of what constitutes a satisfactory bulb are beyond the scope of this CD, however. Suffice it to say that the bulb used in a UV process must be selected with care to insure its appropriateness for the chemistry it is being used with. On a similar note, the chemistry often also has some latitude to be tuned to the spectral output of a given bulb by judicious selection of the photoinitiator package.