A lighting unit uses a discharge lamp (11) as a main source of light supplemented by a filamentary source (12), serving as a resistive ballast. The main lamp is a small, low wattage metal halide lamp of high efficiency. The unit includes a rectifier (15) for conversion of 60 hertz ac to dc, and a dc energized operating network, including a ferrite transformer (20) and a transistor switch (19) driven by an oscillator transistor (30) for starting the discharge lamp. The network has an output adapted to various lamp conditions, including provision of a power boost during glow to arc transition and means for sustaining the arc during transients. The filamentary source provides standby illumination which is substantially constant until proportionately reduced as the main lamp reaches full output. In response to main lamp current and voltage, dc energization is provided during warm-up and normal operation, and energization at above audible frequencies during starting. A dimmer switch (18) is provided.