History of street lighting in the United States
Street lighting in the United States was introduced 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. The first city in the United States to successfully demonstrate electric lighting was Cleveland, Ohio, with twelve electric lights around the Public Square road system on 29 April 1879. Charles F. Brush of Cleveland, Ohio wanted to publicly test his new invention the "Brush light" and needed a city to do so. The city council of Wabash, Indiana agreed to testing the lights and on March 31, 1880, Wabash became the "First Electrically Lighted City in the World" as a flood of light engulfed the town from four Brush lights mounted atop the courthouse. One of the original Brush lights is on display at the Wabash County Courthouse. By the beginning of the 20th century, the number of fire-based streetlights was dwindling as developers were searching for safer and more effective ways to illuminate their streets. Fluorescent and incandescent lights became popular during the 1930s and 1940s, when automobile travel began to flourish. A street with lights was referred to as a white way during the early 20th century. Part of New York City's Broadway was nicknamed the Great White Way due to the massive number of electric lights used on theater marquees lining the street.
Electric light generation methods
Open Arc lamps were used in the late 19th and early 20th century by many large cities for street lighting. Their bright light required that the early arc lamps be placed on rather high (60 to 150-foot) towers; as such, they might be considered the predecessor to today's high-mast lighting systems seen along major highways. They were also widely used in film and stage. Arc lamps use high current between two electrodes (typically carbon rods) and require substantial maintenance. Arc lights have mainly been used where high lumen light was needed such as lighthouses. Today very few open arc lights remain in operation, primarily in a few lighthouses and some industrial uses. The only remaining examples of original street lighting use are the moonlight tower of Austin, Texas.
A xenon lamp is a high pressure sealed arc lamp, and is in common usage today where extreme brightness in a relatively small space is required, typically in motion picture projectors in theaters, and stage and motion picture lighting. The sealed arc lamps do not suffer from the inefficiency and high maintenance problems of the original open arc lamps, but they are not well suited for most street lighting use.
Incandescent lights using a tungsten filament were the first low power electric lights in cities worldwide and introduced some 20 years after open arc lamps[when?]. Some can still be found in streetlight service. Others have been installed in popular downtown areas of major cities to have a nostalgia effect. Incandescent light has excellent Color rendering index rated at 100. Color temperature is generally around 2000–3200 K depending on the type of lamp and replaced the higher maintenance arc lamps.
An incandescent light bulb is less efficient when compared to High-intensity discharge lamp and gas discharge lighting such as Neon light and are being replaced by more efficient LEDs or converted to mains voltage lamps. Tungsten-halogen incandescent lights which are brighter and more efficient and are very commonly used in theatrical and motion picture lighting and better color temperature characteristics are little used in street lighting due to their relatively short lifespan.
Standard incandescent lamps are also very commonly used in traffic signals, although they are increasingly replaced by LEDs.
The fluorescent lamp first became common in the late 1930s. These lamps are a form of discharge lamp where a small current causes a gas in the tube to glow. The typical glow is strong in ultraviolet but weak in visible light. The glass envelope is coated in a mixture of phosphors that are excited by the ultraviolet light and emit visible light. Fluorescent lamps are much more efficient than incandescent lamps, and for a short time became popular in street lighting both because of the efficiency and the novelty value. Fluorescent lamps for street lighting were first introduced to the public for commercial uses at the 1939 World's Fair.
The major problems with standard fluorescent lamps for street lighting is that they are large, and produce a diffused non-directional light. They are also rather fragile. Therefore, the fixtures needed to be large, and could not be mounted more than 20–30 feet above the pavement if they were to produce an acceptable light level.
Fluorescent lamps quickly fell out of favor for main street lighting, but remained popular for parking lot and outside building illumination for roadside establishments.
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 deluxe (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, 75, 100, 175, 250, 400, 700 or 1,000 Watts. The Mercury Vapor lamp is considered obsolete by today's standards and many places are taking them out of service.
As of 2008, the sale of new mercury vapor streetlights and ballasts was banned in the US by the Energy Policy Act of 2005, although the sale of new bulbs for existing fixtures does continue, but the bulbs were also banned in 2015 in Europe. Mercury vapor fixtures can be operated with metal halide lamp (MH) ballasts, and are likely to be rewired with these ballasts in coming years. 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.
High pressure sodium
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. LPS generally were rare in the United States, and common mainly in countries like Hawaii, where there are several famous observatories.
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.
In recent years, metal halide lamp (MH) streetlights have illuminated roadways and parking lots. Metal halide has long been popular in business installations and can be found in warehouses, schools, hospitals and office buildings. Unlike the old mercury lights, metal halide casts a true white light. It is not nearly as popular as its sodium counterparts, as it is newer and less efficient than sodium.
Metal halide lights have also been used for retrofitting. Virtually all fixtures that are converted to metal halide have previously been lit with high-pressure sodium (HPS). MH lamps suffer color shift as they age though this has been improving. Actual life expectancy is about 10,000 to 12,000 hours on average. There has also been a noted issue with the lamps "exploding/shattering" during a failure. Metal Halide light bulbs also tend to dim and/or flicker at the end of their life cycles, and on occasion, cycle. Sometimes, they emit a pinkish glow at or near the end of their life cycle which in this case, the bulb just burns out. High cost and low life hours has kept them from becoming popular municipal lighting sources even though they have a much improved CRI around 85. Therefore, the use of metal halide is limited mainly to city and high end street lighting. They are available in clear or coated bulbs. Probe start MH lights (which are less efficient and are also soon to be banned, unlike Mercury Vapor lamps) come in wattages of 50, 70, 100, 175, 250, 400, and 1000 watt sizes, while pulse start MH lights come in sizes of 50, 70, 100, 150, 200, 250, 320, 350, 400, 450, 750, and 1,000 watt sizes. The wattages of pulse start metal halide lamps are similar to HPS lamp wattages.
Ceramic discharge metal halide lamp
Ceramic discharge metal halide lamps promised to be the next step in streetlighting, replacing old mercury vapor and high pressure sodium lamps, especially where a more clear white with better CRI (78–96) and light color retention was desired. Ceramic metal halide lamps give five times more light than comparable tungsten incandescent light bulbs (80–117 lm/W). However, continuing refinements in LED technology have now surpassed most other lighting types.
An induction lamp features extremely long lamp life (100,000 hours), energy efficiency, high color rendering index, and various color temperatures. The life of induction (also known as electrodeless fluorescent) lamps is negatively affected by heat, particularly as the temperature exceeds 35 degrees Celsius (95 degrees Fahrenheit). Since temperatures in this range commonly occur during early night hours in the summer in much of the US, induction lamp applications have not extended beyond test and demonstration projects for street lighting. The larger size of the induction lamps also inhibits the effective control of the light they emit, limiting their use to lower mounting applications.[according to whom?] In 2009, PSEG in New Jersey began using induction lighting to replace very old and even some pre-2008 mercury vapor lights, and have had success in their reliability and output of the fixtures. Unfortunately, some failed induction lights were spot replaced with the HPS lights that were being removed to begin with and many new installs, PSEG is still using HPS. An updated design of the induction lights is now being used and these seem more reliable and brighter than the original design. Beginning in September 2011 the City of San Diego, CA will replace some 35,000 street lights with induction lamps costing $16,000,000.00. In Mexico, the city of Linares and Acapulco also have begun the replacement of 6,500 and 42,000 street lights with induction lamps, selected for their smart controls, since October 2011. A portion of these street lightswill feature smart grid compatibility to allow the lights to be remotely monitored and controlled via the Internet.
Light emitting diodes
Light emitting diodes (LED) have virtually replaced both incandescent lamps and the occasional fluorescent lamp in traffic signal and crossing sign usage. They are rapidly developing in light output, color rendering, efficiency, and reliability. The cost of LED lighting is still high compared to an incandescent or arc-discharge lamp used for the same purpose, but the cost is decreasing rapidly. Even with the high per-unit cost, the increase in efficiency and increased lifespan make them very attractive for street lighting use. The reduced cost of electricity and maintenance in some cases can offset the increased cost of the lamp.
As with other semiconductors, heat buildup in an LED dramatically reduces its life. The temperature at which this reduction in life occurs is often very near summer evening ambient temperatures. Many of the heat-removal technologies used for other semiconductor applications, such as air conditioning systems, fans, or thermal-transfer fluids, are impractical, maintenance-intensive, or cost-prohibitive for street lighting. Airborne dust from industrial and agricultural activities can impair the functioning of finned heat sinks. Achieving good maintenance-free thermal management in an often hostile environment while keeping product cost competitive is the largest hurdle to the widespread adoption of LED street lights.
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