ET Enterprises Limited manufactures and supplies the long established Electron Tubes brand of photomultiplier tubes and electronics that were previously made by EMI Electronics, Thorn EMI Electronics, and Electron Tubes Ltd. The history of ET Enterprises Limited can be traced back to the 1930s when, as part of EMI, it first became involved with light detection technologies. Specialisation in the development and manufacture of photomultiplier tubes started in the late 1940s, and the company continued to grow to become a major international supplier of low-level light detection devices and systems.