The UVTRON R9533 and R9454 are ultraviolet ON/OFF sensors that utilize the photoelectric effect from metal and gas multiplication. These devices are sensitive only to UV light in a spectral range of 185 nm to 260 nm. This makes them easy to use since they do not require optical visible-cut filters. Their electrodes are optimized for ruggedness to resist mechanical shocks up to 10 times (10000 m/s2) greater than the conventional UVTRONs.

The R9533 is a head-on type (UV light enters through the top of the bulb) that easily installs into equipment. The R9454 is a side-on type (UV light enters through the side of the bulb) whose outer appearance resembles the conventional flame sensor R2868. Both these types utilize a plate cathode and feature high sensitivity and a wide field of view (directivity).