Monochromatic low pressure (LP) and polychromatic medium pressure (MP) ultraviolet (UV) lamp based UV reactors are two commercially available UV systems which are currently being widely used to market water treatment. To ensure proper design and optimize reactor performance, it is important to develop approaches for accurately estimating the germicidal fluence rate distribution within the UV reactor for these UV systems. Spherical actinometry is a technique for determining UV fluence using spherical quartz vessels containing a chemical actinometer. This research combined the spherical actinometry containing iodide/iodate and uridine actinometer with previously developed mathematical analysis to measure germicidal fluence rate distribution in monochromatic and polychromatic UV reactors. Initial results indicated good agreement using two actinometers and reasonable prediction of the fluence rate as compared to previous literature data. The method will be further used to verify the fluence rate distribution predicted in mathematical modeling of UV reactors. Includes 9 references, figures.