History of Street Lighting in The United States - Means of Electric Light Generation - Mercury Vapor

Mercury Vapor

In 1948, the first regular production mercury vapor (MV) streetlight assembly was developed. It was deemed a major improvement over the incandescent light bulb, and shone much brighter than incandescent or fluorescent lights. Initially people disliked them because their bluish-green light made people look like they had the blood drained from them. Other disadvantages are that a significant portion of their light output is ultraviolet, and they "depreciate"; that is, they get steadily dimmer and dimmer with age while using the same amount of energy, and in a few rare instances, they also cycle at the end of their life cycles. Even rarer is they can burn out, especially when the light is being burned while dim (usually at the end of the life cycle). Mercury lamps developed in the mid 1960s were coated with a special material made of phosphors inside the bulb to help correct the lack of orange/red light from mercury vapor lamps (increasing the color rendering index(CRI)). The UV light excites the phosphor, producing a more "white" light. These are known as "color corrected" lamps. Most go by the "DX" designation on the lamp and have a white appearance to the bulb. Mercury Vapor Bulbs come in either clear or coated with powers of 50, 100, 175, 250, 400, 700 or 1,000 Watts. The Mercury Vapor lamp is considered obsolete by today's standards.

As of 2008, the sale of new mercury vapor streetlights and ballasts was banned in the United States by the Energy Policy Act of 2005, although the sale of new bulbs for existing fixtures do continue, but the bulbs will also be banned in 2016 in the USA and Europe. Mercury vapor fixtures can be operated with metal halide lamp (MH) ballasts, and are very likely to be rewired to these ballasts in the years to come. Also, in response to the ban, some older MV streetlights will most likely be modified to use either high pressure sodium or metal halide lamps in the near future, because they are known to last longer than newer luminaires. In some areas where the MV lights are either failing or being replaced, they are being replaced by either HPS, LED, or Induction fixtures of similar lumen output, but also lower wattages and power consumption as well.