Electromagnetic ballasts for HI and HS lamps

As the lamp manufacturer´s reference values regarding lamp current and voltage are generally identical for metal halide (HI) and high-pressure sodium lamps (HS) of the same lamp wattage and the impedance values required for the ballast are also identical, the same ballasts can frequently be used for both lamp types. It should be remembered that HI lamps react sensitively to impedance deviations from the rated value with appreciable colour changes. Vossloh-Schwabe ballasts therefore comply with the lamp´s narrower tolerances. Moreover, the maximum peak direct current value must be observed when operating HI lamps. This value is not specified for HS lamps; instead, the maximum stated start-up current must not be exceeded.
In order to keep the temperature of the luminaires and the electrical values of the lamps within tolerable limits, the impedance of the ballasts must remain constant over the entire service life. A so-called service life test provides proof of this requirement having been met.

HI and HS lamps constitute a special case in terms of thermal testing. In rare cases, a safety risk can occur at the end of the service life of lamps fitted with external bulbs. The safety risk is caused by the so-called lamp rectifier effect, which can lead to overheating of ballasts, ignitors, lamphoders and conductors and can therefore destroy the luminaire. Against this background, the luminaire standard EN 60598-1 "luminaires; part 1: general requirements and tests" has been supplemented by tests concerning this safety risk. As a result, since 1September 2002, it has been illegal to market luminaires that do not comply with the new regulations, i.e. that do not limit the degree to which a lamp heats up in the event of this malfunction. Approvals of luminaires according to the old version of EN 60598 are being withdrawn by the testing institutes. The luminaires are tested using an equivalent circuit, whereby the respective resistors must be dimensioned to suit.