Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it.
Luminaire is a device that changes light distribution of a light source, diffuses the light or eventually changes its spectral composition. This goal is reached by luminous active parts of luminaire (reflector, diffuser, lens, etc.) and auxiliary parts (socket, leads, starter, ballast, etc.) that are designed and constructed for specific light sources. Luminaire is also equipped with parts that are used for fixation, protection of a light source and feeder.
Figure 2.1.1: Simplified functional scheme of LED-based luminaire.