Chemical actinometry of UV germicidal irradiation using sections of quartz tubing as compared with quartz spheres as irradiation vessels has been investigated . Vessels were either 3 mm inner diameter quartz tubing, 46 cm in length (tubular actinometry), or 1 cm quartz spheres (spherical actinometry). The vessels containing an iodide/iodate actinometric solution were suspended from the ceiling at 24 positions in a room (6 × 6 m) containing five germicidal lamp fixtures in the corners and in the center of the room. The lamp fixtures were louvered collimating the radiation in the horizontal (x, y) plane. Hence, the tubes, which span the depth of the radiation field, essentially integrate the radiation along the z-axis for a given x, y position. The pseudospatial average fluence rate obtained using tubular actinometry was 18 mW/cm² for the volume contained in the upper 46 cm (18 inch) of the room. Spherical actinometry, which measured the fluence rate in the center of the beam, provided an average value of 32 mW/cm² over the volume of the beam. A comparison of the fluence rates obtained by these two methods allowed the average depth of the beam to be estimated as 26 cm. It is concluded that tubular actinometry is more advantageous than spherical actinometry for this application.