HID and LPS lamps produce the most light per watt of any light source. They create up to one-third less heat and last as much as 24 times longer than incandescence. Most parking lots and shopping centers use HID lamps, called High Pressure Sodium, since they are especially useful for outdoor security lighting. Despite their advantages, these lamps do have some special characteristics. Like fluorescent, they need special ballast and have a warm-up time of three to seven minutes, making them unsuitable for some situations.
Watts measure the amount of energy going into a bulb.
Lumens measure the light output or brightness of a bulb. This information is printed on bulb packages. To determine efficiency, divide the lumens by the watts of electricity used. Fluorescent lighting delivers three to four times the light of incandescent bulbs of the same wattage and lasts up to 10 times longer. The filament in light bulbs is sensitive to vibration and voltage.