4.1 Introduction4.2 Properties of a source4.2.1 Spectral output4.2.2 Colour temperature4.2.3 Directional properties4.2.4 Polarization4.2.5 Duration4.2.6 Operational factors4.3 Daylight4.4 Moonlight and starlight4.5 Tungsten filament sources4.6 Fluorescent lighting4.7 Discharge sources4.8 Luminescent sources4.9 Flash sources4.9.1 Expendable flashbulb4.9.2 Argon bomb4.9.3 Spark sources4.9.4 Electronic flash4.9.5 Stroboscope4.9.6 Microflash unit4.9.7 Flash X-ray source4.10 Laser sources4.10.1 Lasers4.10.2 Types of laser4.10.3 Applications4.11 Radiation sourcesReferences and further reading