page_title: History of street lighting in the United States
section_title: High pressure sodium
hierarchical_section_title: History of street lighting in the United States / Electric light generation methods / High pressure sodium
caption_attribution_description: English: Example of a high pressure sodium vapor streetlight
context_page_description: Street lighting in the United States was introduced to the US by inventor Benjamin Franklin, who was the postmaster of Philadelphia, Pennsylvania. For this reason, many regard Philadelphia as the birthplace of street lighting in the US.
  The colonial-era streetlights were lit by candles placed inside a glass vessel, which kept the candle from being blown out by wind. Franklin's design was four-sided, with four separate panes of glass, so that if one pane of glass was broken, the lamp did not need to be entirely replaced, and might not even blow out.
  After the invention of gas lighting by William Murdoch in 1792, cities in Britain began to light their streets using gas. The United States followed suit shortly afterwards with the introduction of gas lighting to Pelham Street in Newport, Rhode Island, in 1803. Throughout the 19th century, the use of gas lighting increased. Some locations in the US still use gas lights.
  After Thomas Edison pioneered electric use, light bulbs were developed for the streetlights as well.
context_section_description: Around 1970, a new lamp was invented: The high pressure sodium (HPS) light. They became common in the late 1980s. It was initially disliked by most residents because of its orange glow, but the sodium vapor streetlight has since become the dominant type on American roadways and most people have become accustomed to the orange/yellow glow. Color-corrected sodium vapor lamps exist but are expensive. These "color corrected" HPS lamps have lower life and are less efficient.
  There are two types of sodium vapor streetlights: high-pressure (HPS) and low-pressure (LPS). Of the two, HPS is the more-commonly used type, and it is found in many new streetlight fixtures. Sometimes, older (pre-1970) fixtures may be retrofitted to use HPS lights as well. Virtually all fixtures that are converted to HPS have previously been lit with mercury vapor.
  LPS lights are even more efficient than HPS, but produce only a single wavelength of yellow light, resulting in a CRI of zero, meaning colors cannot be differentiated. LPS lamp tubes are also significantly longer with a less intense light output than HPS tubes, so they are suited for low mounting height applications, such as under bridge decks and inside tunnels, where the limited light control is less of a liability and the glare of an intense HPS lamp could be objectionable. Many LPS lights are also being changed out to HPS using FCO fixtures, or going to LED.
  HPS lamps have slightly different electrical requirements than do the older MV lamps. Both HPS and MV lamps require a transformer or ballast to change the voltage and regulate the current, however, HPS lamps also require an electrical "starter" circuit—much like older fluorescent lamps in residential use. MV lamps do not require a separate "starter" circuit because they have a special starter element within the bulb used for striking the arc. MV lamps slowly dim over time, and a 20-year-old lamp may emit a very pleasing, but useless, soft green glow, rather than the powerful blue-white light of a new MV lamp. The yellow-spectrum HPS lamps also slowly dim over time but are known for "cycling," where the lamp cycles on and off when it has reached the end of its life cycle. When cycling, the arc within the lamp extinguishes and the lamp must cool down before the starter circuit initializes a new arc. This has been the most recognized downfall of HPS. Some HPS lamps start to burn a pinkish/reddish color at the end of their life (usually when already cycling), or start to burn a pinkish/white color and go dim, or also burn out at the end of their life cycle whether they cycle or not. HPS fixtures can contain a special photocell or ballast that can sense a cycling lamp and shut off the fixture to prevent damage to the ignitor and ballast.
  HPS lamps generally have the same rated lifespan as MV lamps, and they give increased light and efficiency at lower wattages. Usually, when an MV light is replaced, it is replaced with a HPS light of a lower wattage, for example, a 175 watt MV fixture will get replaced with a 100 or 150 watt HPS fixture as that will meet or exceed the lumen output of the 175 watt MV fixture. At end of life MV lamps just become dimmer and sometimes color shift towards the green end of the spectrum but continue to consume the same amount of electricity. HPS lamps begin to suffer end-of-life cycling before the amount of useful light becomes visibly diminished, or just burn out. HPS lights come in wattages of 35, 50, 70, 100, 150, 200, 250, 310, 400, 600, 750, and 1,000 watt sizes, while LPS lights come in wattages of 18, 35, 55, 90, 135, and 180 watt sizes.
  Although the use of HPS is dramatically decreasing in many large cities, it is still a popular form of use in grow lights, as seen in greenhouses, aquariums and planetariums.
caption: Example of a high-pressure sodium vapor streetlight
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