The H7422 series are photosensor modules with an internal high-voltage power supply circuit and a cooler installed to the metal package photomultiplier tube. Efficient cooling was achieved by placing the cooler near the photomultiplier tube to reduce thermal noise emitted from the photocathode and a high S/N ratio can be obtained even at extremely low light levels. The H7422-40 has high sensitivity in the 300 nm to 720 nm wavelengths. The H7422-50 is sensitive along a wide spectral range from 380 nm to 890 nm. The H7422-01, H7422-02 and H7422-20 have a maximum output current value of 100 A and so are extremely effective when measurements are needed over a wide dynamic range. The photomultiplier tube is maintained at a constant temperature by monitoring the output from a thermistor installed near the photomultiplier and then regulating the current to the thermoelectric cooler.