Since radioactivity was discovered around the beginning of the 20th century, the main application of radioluminescence has been in radioluminescent paint, used on watch and compass dials, gunsights, aircraft flight instrument faces, and other instruments, allowing them to be seen in darkness.  Radioluminescent paint consists of a mixture of a chemical containing a radioisotope with a radioluminescent chemical (phosphor).  The continuous radioactive decay of the isotope's atoms releases radiation particles which strike the molecules of the phosphor, causing them to emit light.  The constant bombardment by radioactive particles causes the chemical breakdown of many types of phosphor, so radioluminescent paints lose some of their luminosity during their working life.
Radioluminescent materials may also be used in the construction of an optoelectric nuclear battery, a type of radioisotope generator in which nuclear energy is converted into light.