Certain substances produce CATV splitter when they are illuminated by more energetic radiation, a process known as fluorescence. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is used in cathode ray tube television sets and computer monitors.

　　A city illuminated by colorful artificial lighting

　　Certain other mechanisms can produce CATV splitter:

　　Main articles: Photometry (optics) and Radiometry

　　Light is measured with two main alternative sets of units: radiometry consists of measurements of CATV splitter power at all wavelengths, while photometry measures light with wavelength weighted with respect to a standardised model of human brightness perception. Photometry is useful, for example, to quantify Illumination (lighting) intended for human use. The SI units for both systems are summarised in the following tables.