HID lights are most often employed outdoors where generous amounts of light are needed like in parking lots and along streets and highways. Indoors they are used in greenhouse and warehouse-type settings. Halogen bulbs are mostly used indoors like standard incandescent light bulbs. Many automobile headlights employ halogen light bulbs.
Several different types of HID light bulbs are available to consumers. Some of the most widely used HID light bulbs are high-pressure sodium bulbs and metal halide bulbs.
Halogen light bulbs do not last for nearly as long as HID light bulbs. According to the California Energy Commission, halogen light bulbs typically last for between 2,000 and 6,000 hours. High-pressure sodium light bulbs can last for anywhere between 12,000 and 24,000 hours, while metal halide light bulbs can last for anywhere between 10,000 and 15,000 hours.
The intensity of light sources is measured in lumens. Halogen bulbs produce around 20 lumens per watt. A 250-watt high-pressure sodium bulb produces around 87 lumens per watt, while metal halide bulbs of the same wattage produce around 58 lumens per watt.
Around 15 mg of elemental mercury is contained in a 250-watt high pressure sodium bulb, while around 38 mg of elemental mercury is contained in a metal halide bulb of the same wattage. There is no mercury found in halogen light bubs of any wattage.