After ignition High-pressure Discharge Lamps generally require a run-up time of up to 10 min. before they develop full Luminous Flux and gas discharge is stabilised (cf. Igniter).

To bridge this period, in which neither illuminance nor Color Appearance conform to lamp rating, an auxiliary lamp with instant start characteristics can be incorporated in the luminaire.

The auxiliary light source provides the minimum required illuminance. Once the primary lamp has stabilised, the auxiliary is switched off. Should the high-pressure lamp be extinguished briefly, the auxiliary circuit is again employed until Reignition occurs.