History Of Streetlights
Lack of natural light during nighttime was always a problem, for everyone. From basic inconvenience that people cannot see where they are going to the greater chance of being attacked or mugged during the night. Because the problem was there since humans started living together, history of street light is maybe longer than we think.
It is known that natural gas was led through bamboo pipes from volcano gas leaks to the streets of Peking to serve as a fuel for street lamps and that as early as 500 years BC. Ancient Romans used oil lamps filled with vegetable oil in front of their houses and had special slaves whose only duty was to take care of those lamps, to light them, extinguish them and watch that they always have oil. First organized method of public lightning was done on 1417, when Mayor of London, Sir Henry Barton first ordained that by law all houses must hang lanterns outside when night falls during the winter months. Paris street were illuminated first time by order in 1524 that said that all houses must have light in the windows at night if they face the streets. One more method to brighten the streets at nights were “link-boys”, children servants that wealthy citizens of London paid to carry torches while accompanying them through the city (practice that was sometimes dangerous because they sometimes led their costumers into dark alleys to be mugged by footpads).
Era of more efficient street lightning starts with William Murdock who, for the first time in 1802, lit the outside of the Soho Foundry in a public presentation with a gas light fueled with coal gas. After that, in 1807, London got its first gas lit street. Baltimore was the first city in the United States that started using gas for streetlight in 1816 while Paris started gas illumination of its streets in 1820. Gas was led through pipe installations to the gas lanterns that were placed on poles. Every evening the lamplighters, men whose job was to take care of the gas streetlights, were lighting the lanterns and every morning they were putting them off. This was done until the invention of the mechanism that lit the lamps when the gas was released in the lamp. After that came electricity and made street lightening even more efficient.
First electric streetlight used arc lamps, namely “Yablochkov candle”. It was first used in 1878 in Paris. By 1881, some 4000 were in use, replacing gas lanterns on the poles. After the spreading of the arc lamps in the United States, by 1890 there were more than 130,000 arc lamps installed as streetlights. Most of them were installed on the tops of so-called “moonlight towers” – tall, metal constructions that illuminated more city blocks at once. Arc lights had two major flaws: they made strong, harsh light and they did not last long. So in time they were replaced with incandescent lamps that were cheaper, brighter and lasted longer, while arc lamps remained useful on industrial sites. Today, streetlights use high-intensity discharge lamps, mostly HPS high-pressure sodium lamps.
Some of the electric light generation methods in order are –
1) Arc lamp
Open Arc lamps were used in the late 19th & 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.
2) Incandescent light
By far the most recognized type of lighting is the incandescent light bulb using a tungsten filament. These were the first low power electric lights in cities worldwide. Some can still be found in streetlight service, although many of them are using more efficient CFL light bulbs and some have been converted to MV or HPS. Others have been installed popular downtown areas of major cities to have a nostalgia effect. They were introduced some 20 years after open arc lamps, and in many cases replaced the higher maintenance arc lamps.Tungsten-halogen incandescent lights are more efficient than regular incandescent lights, and are very commonly used in theatrical and motion picture lighting due to their higher efficiency and brightness and better color temperature characteristics. They are little used in street lighting due to their relatively short lifespan.
Standard incandescent lamps are very commonly used in traffic signals, although are increasingly being replaced by LEDs.
3) Fluorescent lamp
The fluorescent 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 quickly fell out of favor for main street lighting, but remained popular for parking lot and outside building illumination for roadside establishments.
4) 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 bulbs, 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.
5) High pressure sodium
Around 1970, a new streetlight was invented: The high pressure system (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. It is by far the most efficient light source available. 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.
6) Metal halide
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.
7) 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. CDM 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.
8) Induction lamp
An induction lamp features extremely long lamp life (100,000 hours), energy efficiency, high color rendering index, and a color temperature close to incandescent lights. The life of induction (also known as electrode less 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.
9) Compact fluorescent lamp
Compact fluorecent lamp (CFL) have been used more frequently as time has improved the quality of these lamps. These lamps have been used on municipal walkways and street lighting though they are still rare at this time. Improvements in reliability still need to be made. Some issues with them are limited lumen output, high heat build up in the self-contained ballast, low life/burnout due to frequent cycling (on/off) of the lamp, and the problem where most fluorescent sources become dimmer in cold weather (or fail to start at all). CFL efficiency is high and CRI is excellent around 85. CFL produces a color temperature around 3000 K with its light being “soft white” around that color temperature. Higher color temperatures are available.
10) Light emitting diodes
Light Emitting diode (LED) have virtually replaced both incandescent lamps and the occasional fluorescent lamp in traffic control 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 many cases can offset the increased cost of the lamp.