Standard optical detectors, such as avalanche photodiode, photomultiplier tube (PMT) or CCD, can be used. Photodiode arrays and photomultiplier tubes were common prior to the adoption of CCDs. The photons are detected using a photomultiplier tube. This translates into a pulse from the photomultiplier of voltage proportional to the photon energy. NaI detectors are usually composed of a NaI crystal coupled with a photomultiplier. In either case, the photomultiplier can detect individual photons. The emitted light is filtered and detected by a photomultiplier tube. Light reflected off the colored stripes was read by photomultiplier vacuum tubes. These filters were specified as particular combinations of glass filters and photomultiplier tubes. Each array has 12 cylindrical counters equipped with a quartz radiator and a photomultiplier tube. The array contains a set of twelve separate vertical strings of photomultiplier tubes. The detection is done via CCD or a photomultiplier tube. It consists of 50,000 tons of pure water surrounded by about 11,200 photomultiplier tubes. The Cherenkov light is recorded by the photomultiplier tube. Some of the 11,146 photomultiplier tubes are on display at the Miraikan in Tokyo.