This process starts when a photon enters the vacuum tube and hits a special metal plate. This starting plate is known in chemistry as a photocathode. When the photon strikes the photocathode, it knocks a single electron loose.
This escaping electron then speeds toward a second metal plate called a dynode. The fast electron crashes into the dynode and knocks loose several new electrons. These new electrons accelerate toward a third plate to repeat the crash.
This cascading chain reaction continues across a series of ten or more dynodes. The number of moving electrons grows exponentially with every single dynode collision. Finally, a collector plate gathers millions of electrons to form a measurable electric current.
Students sometimes think these tubes simply make the original light physically brighter. Instead, the tube converts the light into an electrical signal and amplifies that electricity. These sensors are crucial for analytical chemistry techniques like fluorescence spectroscopy.
They let chemists measure trace amounts of chemicals hidden in large liquid samples. Without this massive amplification, the original light signal would be totally invisible.