Street lighting is supplied by local distribution systems at 120/240 V and is generally the only service for which the electric utility installs, operates and maintains utilization equipment. The lights that illuminate roads and highways generally use high-intensity discharge lamps with ballasts compatible with common voltages and may be either high- or normal-power factor. High-intensity discharge lamps are usually phosphor-coated mercury, metal halide, or highpressure sodium. Lamps are available in sizes ranging from 100 to 1,000 watts (W) and may be sealed or filtered for longer life. Photoelectric controls are usually used with individual lights. Most utility lighting systems have been mounted on existing overhead support structures; however, for underground systems lighting can be designed with supply run from the nearest transformer or handhole.