October 2017
Intermediate to advanced
214 pages
6h 49m
English
Certain substances, such as some minerals, paint pigments, inks, liquids, moulds and plant tissues, when illuminated (‘excited’) by shortwave radiation, emit radiation of a longer wavelength, which is sometimes visible to the human eye. Such emissions are known as luminescence, of which there are several types, including phosphorescence and fluorescence. Fluorescence fades almost immediately after the removal of the light source, whilst substances which continue to emit light after the light source has been removed are said to be phosphorescent. Cathode ray tube (CRT) television screens and oscilloscopes are phosphorescent systems, where an electron beam sweeps across the screen, ...