If the electrical current through a discharge lamp is increased, a discharge channel with very high luminous efficiency is created in the discharge chamber; luminous flux and light output increase substantially. The internal pressure of the discharge chamber rises and attains between 1and 10 bar these are so-called high-pressure discharge lamps (general: discharge lamp). The light output and colour rendition of high-pressure lamps vary considerably depending on the lamp family.
Discharge lamps can only be operated with ballasts. Ignitors are additionally required for sodium lamps and metal halide lamps. Furthermore, to compensate blind current when using magnetic ballasts, compensation capacitors must be fitted. The lampholders enable the lamp to be fixed in the luminaire and ensure simple exchange of lamps at the end of their service life. As well as stabilising the lamp´s operating point, ballasts also influence the lamp´s output and luminous flux, the system´s light output, the service life of the lamps as well as the colour temperature of the light
High-pressure sodium lamps (HS lamps)
Metal halide lamps (HI lamps)
Metal halide lamps with a ceramic discharge tube (C-HI lamps)
Mercury vapour lamps (HM lamps)
Low-pressure sodium lamps (LS lamps)
Ballasts can be of either electromagnetic or electronic construction. Unlike with fluorescent lamps, lamp efficiency is not decisively altered by the use of electronic ballasts. In contrast, electronic ballasts lead to a reduction of the inherent losses and thus to an increase in system efficiency. In addition, electronic ballasts ensure gentle lamp operation, which increases the lamp´s service life.
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