Street lights, also called street lamps, are sources of light affixed above roadways, parking lots, and sidewalks to enhance the vision of passersby during nighttime and dark weather. These devices are positioned atop dedicated poles or utility poles, and focus a pool of light to the ground below. These devices are primarily used to illuminate items not within the focus of headlight beams, such as signs and obstacles; they do not illuminate a driving route. Street lamps also help deter criminal activity during between dusk and dawn, and wide-focus lamps are produced to promote safety. Street lamps are used sparingly to reduce light pollution and energy use, as well as to minimize a driver's acclimation to night vision. The lamps commonly utilize incandescent, high pressure sodium, low pressure sodium, mercury vapor, metal halide, and high intensity discharge bulbs. Many lamp designs are available to promote both functional and aesthetic selection.