High-intensity discharge (HID) lamp dimming has grown in popularity in recent years. Dimming HID lamps can result in energy savings, peak demand reduction and greater flexibility in multi-use spaces. Dimming reduces energy costs by reducing the input power to the lighting system. It can be used to
reduce peak demand and therefore reduce costly utility demand charges that can be a significant component of the total utility cost. And it offers greater flexibility to adapt spaces to different uses. Dimming can be employed in HID lighting systems to save energy, and enable the space to adapt to different uses, ambient conditions and time of day.“HID dimming saves energy and thereby reduces owner operating costs,” says A. J. Glaser, President of the Lighting Controls Association and Colorado-based HUNT Dimming. “It also maximizes end-user satisfaction by providing proper light levels.” Save energy: Dimming can be used to save energy during periods when the space is unoccupied but needs to stay lighted for safety and security reasons. Dimming can be achieved either manually via input from a switch or automatically via input from a control device. Automatic dimming can be set to respond to a preset schedule or variable ambient conditions such as occupancy and available daylight. Occupancy. Dimming is a highly practical control method for saving energy with HID lighting systems to address periods of non-occupancy in spaces that must be constantly lighted. High pressure sodium lamps can take 3-5 minutes to warm up; they take less than a minute to hot-restrike but don't reach full light for 3-4 minutes. Metal halide lamps take 2-10 minutes to warm up and 12-20 to hot-restrike, while pulse-start metal halide lamps take 1-2 minutes. Given these characteristics, it is not practical to shut off and restart the lamps based on occupancy if the space must be made usable again quickly. In these situations, the lamps must be operated continuously, resulting in energy waste. In addition, most lamp manufacturers rate HID lamp life at a minimum of 10 hours per start. Any reduction in burn time per start below this minimum will result in shorter lamp life. If the lamps are dimmed instead in response to a signal from an occupancy sensor or time-programmable controller indicating the space is unoccupied, significant energy savings can occur during these periods, but the lamps will be able to achieve full light output quickly when the space becomes occupied again. If occupation of the space is predictable, then timers or other time-programmable controllers may be used to deliver the control signal to dim the lamps. If occupation of the space is not predictable, then occupancy sensors may be used. Daylight harvesting. Dimming can be used to adjust light levels based on available daylight via input from a photocell. Peak demand reduction. Dimming can be scheduled using a time-programmable controller during times of peak demand, shaving the facility’s peak demand and potentially reducing utility demand charges. Flexibility: HID lighting systems are fixed output systems, but spaces may require different light levels because they are used for multiple purposes. Dimming makes the lighting system flexible and adaptive to different uses of the space. A school gym, for example, can be dimmed to provide suitable lighting for sports, social events, maintenance and other uses. A wholesale outlet can be dimmed during maintenance and stocking