High intensity discharge (HID) is light from a plasma discharge rather than a filament. The system involves a ballast to start the light and certain gasses to create the light. HID lighting uses less energy than halogen but produces three times more light. Light is created from an electrical discharge between two electrodes in a micro-environment of xenon gas and metal halide salts. The light is emitted by an electrically energized gas - a plasma discharge - formed and sustained between the two electrodes. The distinctive blue-white light of HID lamps stimulates the reflective paints in road markers and signs creating a safer driving environment. Additionally, the increased light output is designed to illuminate a wider area in front of the vehicle, improving visibility and safety without disturbing the vision of oncoming drivers. On November 6, 2009, Osram Sylvania announced the release of a HID fact sheet designed to help educate the media and the public on the truths behind HID automotive lighting. The Facts About HID document features briefs on recent studies proving that HID headlamps provide visual benefits that may lead to greater nighttime driving safety for people -- and animals -- alike. Approximately 1.5 million deer/vehicle collisions occur each year in the U.S., resulting in $1.1 billion in damage, injuries to occupants and loss of individual animals according to the Insurance Institute for Highway Safety.
A recent study by the U.S. Department of Agriculture tested the effects of halogen and HID headlights on the flight-initiation distance (FID) of free-range deer. Flight-initiation distance is defined as the distance at which the deer sees the vehicle as runs from the roadway. The study hypothesized that a vehicle lighting system that better complemented the visual capabilities of deer at night would increase the distance that deer perceived an oncoming vehicle, giving them more time to leave the roadway, potentially reducing the number of deer/vehicle collisions. The results of the eight-month study proved the premise to be true. White-tailed deer were more sensitive to a vehicle equipped with HID lighting, taking flight up to 20 meters sooner than they did when exposed to a vehicle equipped with halogen lamps. Results also proved that HID headlamps increase visual awareness of objects in the driver's peripheral vision. That benefit would extend to people walking along the roadway as well. Additionally, researchers discovered that the spectral power distribution (SPD) or physical makeup of the HID light beam makes it easier for the human eye to see objects in low-light conditions.