Phototube

A phototube or photoelectric cell is a special kind of tube that can sense light. It is either filled with gas or a vacuum, which helps it work. These tubes are very good at detecting light and were used a lot in the past. Today, many uses have switched to newer, solid-state light detectors, but some types, like the photomultiplier tube, are still important in science research because they can detect even very tiny amounts of light.

Operating principles

Phototubes work using a special effect called the photoelectric effect. When light, made of tiny particles called photons, hits a part of the tube called the photocathode, it can push out tiny particles called electrons. These electrons are pulled towards another part called the anode, creating a flow of electricity. This flow changes based on how bright and what type of light is shining on the tube.

Different materials used to make the photocathode let the tube see different colors of light better. Some materials work best with blue and purple light, while others can see red and infrared light better. Tubes with no gas inside give a steady flow of electricity when lit, while tubes filled with a little gas can detect weaker light but react more slowly to quick changes in light.

Applications

Phototubes helped read the sound tracks on old films. They were used to sense light in many ways. Now, some of these jobs are done by newer parts called photoresistors and photodiodes.