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Sodium-vapor lamp

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.

A high-pressure sodium street light in Toronto
A high-pressure sodium-vapor lamp

Two varieties of such lamps exist: low-pressure and high-pressure. Low-pressure sodium lamps are highly efficient electrical light sources, but their yellow light restricts applications to outdoor lighting, such as street lamps, where they are widely used. High-pressure sodium lamps emit a broader spectrum of light than the low-pressure lamps, but they still have poorer color rendering than other types of lamps. Low-pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night.

Contents

The low-pressure sodium arc discharge lamp was first made practical around 1920 owing to the development of a type of glass that could resist the corrosive effects of sodium vapor. These operated at pressures of less than 1 Pa and produced a near monochromatic light spectrum around the sodium emission lines at 589.0 and 589.56 nanometres wavelength. The yellow light produced by these limited the range of applications to those where color vision was not required.

Research into high-pressure sodium lamps occurred in both the UK and the US. Increasing the pressure of the sodium vapor broadened the sodium emission spectrum so that the light produced had more energy emitted at wavelengths above and below the 589 nm region. The quartz material used in mercury discharge lamps was corroded by high pressure sodium vapor. A laboratory demonstration of a high pressure lamp was carried out in 1959. The development by General Electric of a sintered aluminum oxide material (with magnesium oxide added to improve light transmission) was an important step in construction of a commercial lamp. The material was available in the form of tubing by 1962, but additional techniques were required to seal the tubes and add the necessary electrodes—the material could not be fused like quartz. The end caps of the arc tube would get as hot as 800 degrees C in operation, then cool to room temperature when the lamp was turned off, so the electrode terminations and arc tube seal had to tolerate repeated temperature cycles. This problem was solved by Michael Arendash at the GE Nela Park plant. The first commercial high-pressure sodium lamps were available in 1965 from companies in the United States, the United Kingdom, and the Netherlands; at introduction a 400 watt lamp would produce around 100 lumens per watt.

Single-crystal artificial sapphire tubes were also manufactured and used for HPS lamps in the early 1970s, with a slight improvement in efficacy, but production costs were higher than for polycrystalline alumina tubes.

An unlit 35 W LPS/SOX lamp
Warm-up phases of a LPS lamp. The faint pink light of the Penning mixture is gradually replaced by the bright monochromatic orange light of the metallic sodium vapor.
A running 35 W LPS/SOX lamp
Spectrum of a low-pressure sodium lamp. The intense yellow band is the atomic sodium D-line emission, comprising about 90% of the visible light emission for this lamp type.
Two Honda Fits under low-pressure sodium lamps. Both appear black, even though the car on the left is bright red, while the car on the right is actually black.

Low-pressure sodium (LPS) lamps have a borosilicate glass gas discharge tube (arc tube) containing solid sodium and a small amount of neon and argon gas in a Penning mixture to start the gas discharge. The discharge tube may be linear (SLI lamp) or U-shaped. When the lamp is first started, it emits a dim red/pink light to warm the sodium metal; within a few minutes as the sodium metal vaporizes, the emission becomes the common bright yellow. These lamps produce a virtually monochromatic light averaging a 589.3 nm wavelength (actually two dominant spectral lines very close together at 589.0 and 589.6 nm). The colors of objects illuminated by only this narrow bandwidth are difficult to distinguish.

LPS lamps have an outer glass vacuum envelope around the inner discharge tube for thermal insulation, which improves their efficiency. Earlier LPS lamps had a detachable dewar jacket (SO lamps). Lamps with a permanent vacuum envelope (SOI lamps) were developed to improve thermal insulation. Further improvement was attained by coating the glass envelope with an infrared reflecting layer of indium tin oxide, resulting in SOX lamps.

LPS lamps are among the most efficient electrical light sources when measured in photopic lighting conditions, producing above 100 and up to 206 lm/W. This high efficiency is partly due to the light emitted being at a wavelength near the peak sensitivity of the human eye. They are used mainly for outdoor lighting (such as street lights and security lighting) where faithful color rendition is not important. Recent studies show that under typical nighttime mesopic driving conditions, whiter light can provide better results at a lower level of illumination.

LPS lamps are similar to fluorescent lamps in that they are a low-intensity light source with a linear lamp shape. They do not exhibit a bright arc as do High-intensity discharge (HID) lamps; they emit a softer luminous glow, resulting in less glare. Unlike HID lamps, during a voltage dip low-pressure sodium lamps return to full brightness rapidly. LPS lamps are available with power ratings from 10 W up to 180 W; longer lamp lengths can, however, suffer design and engineering problems.

Modern LPS lamps have a service life of about 18,000 hours and do not decline in lumen output with age, though they do increase in energy consumption by about 10% towards end of life. This property contrasts with mercury vapor HID lamps, which become dimmer towards the end of life to the point of being ineffective, while consuming undiminished electrical power.

In 2017 Philips Lighting, the last manufacturer of LPS lamps, announced they were discontinuing production of the lamps due to falling demand. Initially, production was due to be phased out in the course of 2020, however this date was brought forward and the last lamps were produced at the Hamilton factory in November 2019.

Light pollution considerations

For locations where light pollution is a consideration, such as near astronomical observatories or sea turtle nesting beaches, low-pressure sodium is preferred (as formerly in San Jose and Flagstaff, Arizona). Such lamps emit light on just two dominant spectral lines (with other much weaker lines), and therefore have the least spectral interference with astronomical observation. (Now that production of LPS lamps has ceased, consideration is being given into the use of narrow-band amber LEDs, which are on a similar color spectrum to LPS.) The yellow color of low-pressure sodium lamps also leads to the least visual sky glow, due primarily to the Purkinje shift of dark-adapted human vision, causing the eye to be relatively insensitive to the yellow light scattered at low luminance levels in the clear atmosphere. One consequence of widespread public lighting is that on cloudy nights, cities with enough lighting are illuminated by light reflected off the clouds. Where sodium vapor lights are the source of urban illumination, the night sky is tinged with orange.

Film special effects

Sodium vapor process (occasionally referred to as yellowscreen) is a film technique that relies on narrowband characteristics of LPS lamp. Color negative film is typically not sensitive to the yellow light from an LPS lamp, but special black-and-white film is able to record it. Using a special camera, scenes are recorded on two spools simultaneously, one with actors (or other foreground objects) and another that becomes a mask for later combination with different background. This technique originally yielded results superior to blue-screen technology, and was used in years 1956 to 1990, mostly by Disney Studios. Notable examples of films using this technique include Alfred Hitchcock's The Birds and the Disney films Mary Poppins and Bedknobs and Broomsticks. Later advancements in blue- and green-screen techniques and computer imagery closed that gap, leaving SVP economically impractical.

High-pressure sodium lamp in operation
Spectrum of high-pressure sodium lamp. The yellow-red band on the left is the atomic sodium D-line emission; the turquoise line is a sodium line that is otherwise quite weak in a low pressure discharge, but becomes intense in a high-pressure discharge. Most of the other green, blue, and violet lines arise from mercury.
Diagram showing the spectral output of a typical high-pressure sodium (HPS) lamp.
Office building illuminated by high-pressure sodium lamps.
High-pressure sodium lamp Philips SON-T Master 600 W

High-pressure sodium (HPS) lamps have been widely used in industrial lighting, especially in large manufacturing facilities, and are commonly used as plant grow lights. They contain mercury. They have also been widely used for outdoor area lighting, such as on roadways, parking lots, and security areas. Understanding the change in human color vision sensitivity from photopic to mesopic and scotopic is essential for proper planning when designing lighting for roadways.

High-pressure sodium lamps are quite efficient — about 100 lumens per watt, when measured for photopic lighting conditions. Some higher-power lamps (e.g. 600 watt) have efficacies of about 150 lumens per watt.

Since the high-pressure sodium arc is extremely chemically reactive, the arc tube is typically made of translucent aluminum oxide. This construction led the General Electric Company to use the tradename "Lucalox" for its line of high-pressure sodium lamps.

Xenon at a low pressure is used as a "starter gas" in the HPS lamp. It has the lowest thermal conductivity and lowest ionization potential of all the stable noble gases. As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp. The low thermal conductivity minimizes thermal losses in the lamp while in the operating state, and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state, which allows the lamp to be easily started.

"White" SON [expand acronym]

A variation of the high-pressure sodium introduced in 1986, the White SON has a higher pressure than the typical HPS/SON lamp, producing a color temperature of around 2700 kelvins with a color rendering index (CRI) of about 85, greatly resembling the color of an incandescent light. These lamps are often used indoors in cafes and restaurants for aesthetic effect. However, white SON lamps have higher cost, shorter service lives, and lower light efficiency, and so they cannot compete with HPS at this time.

Theory of operation

This section does not cite any sources. Please help improve this section by . Unsourced material may be challenged and removed.(December 2017) ()
Diagram of a high-pressure sodium lamp.

An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor that is needed to draw an arc. The temperature of the amalgam is determined to a great extent by lamp power. The higher the lamp power, the higher will be the amalgam temperature. The higher the temperature of the amalgam, the higher will be the mercury and sodium vapor pressures in the lamp and the higher will be the terminal voltage. As the temperature rises, the constant current and increasing voltage consumes increasing energy until the operating level of power is reached. For a given voltage, there are generally three modes of operation:

  1. The lamp is extinguished and no current flows.
  2. The lamp is operating with liquid amalgam in the tube.
  3. The lamp is operating with all amalgam evaporated.

The first and last states are stable, because the lamp resistance is weakly related to the voltage, but the second state is unstable. Any anomalous increase in current will cause an increase in power, causing an increase in amalgam temperature, which will cause a decrease in resistance, which will cause a further increase in current. This will create a runaway effect, and the lamp will jump to the high-current state (#3). Because actual lamps are not designed to handle this much power, this would result in catastrophic failure. Similarly, an anomalous drop in current will drive the lamp to extinction. It is the second state that is the desired operating state of the lamp, because a slow loss of the amalgam over time from a reservoir will have less effect on the characteristics of the lamp than a fully evaporated amalgam. The result is an average lamp life in excess of 20,000 hours.

In practical use, the lamp is powered by an AC voltage source in series with an inductive "ballast" in order to supply a nearly constant current to the lamp, rather than a constant voltage, thus assuring stable operation. The ballast is usually inductive rather than simply being resistive to minimize energy waste from resistance losses. Because the lamp effectively extinguishes at each zero-current point in the AC cycle, the inductive ballast assists in the reignition by providing a voltage spike at the zero-current point.

The light from the lamp consists of atomic emission lines of mercury and sodium, but is dominated by the sodium D-line emission. This line is extremely pressure (resonance) broadened and is also self-reversed because of absorption in the cooler outer layers of the arc, giving the lamp its improved color rendering characteristics. In addition, the red wing of the D-line emission is further pressure broadened by the Van der Waals forces from the mercury atoms in the arc.

This section does not cite any sources. Please help improve this section by . Unsourced material may be challenged and removed.(December 2017) ()
Sodium vapor street light
Closeup after dark

At end of life, high-pressure sodium (HPS) lamps exhibit a phenomenon known as cycling, caused by a loss of sodium in the arc. Sodium is a highly reactive element and is lost in a reaction with the aluminum oxide of the arc tube. The products are sodium oxide and aluminum:

6 Na + Al2O3 → 3 Na2O + 2 Al

As a result, these lamps can be started at a relatively low voltage, but, as they heat up during operation, the internal gas pressure within the arc tube rises, and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the maximum voltage output by the electrical ballast. As the lamp heats to this point, the arc fails, and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, typically starting at a pure or bluish white then moving to a red-orange before going out.

More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles, as the repeated high-voltage ignitions needed to restart the arc reduce the lifetime of the ballast. If power is removed and reapplied, the ballast will make a new series of startup attempts.

LPS lamp failure does not result in cycling; rather, the lamp will simply not strike or will maintain the dull red glow of the start-up phase. In another failure mode, a tiny puncture of the arc tube leaks some of the sodium vapor into the outer vacuum bulb. The sodium condenses and creates a mirror on the outer glass, partially obscuring the arc tube. The lamp often continues operating normally, but much of the light generated is obscured by the sodium coating, providing no illumination.

Power output ANSI codes
35 W S76
50 W S68
70 W S62
100 W S54
150 W S55 (55v) or S56 (100v)
200 W S66
250 W S50
310 W S67
400 W S51
600 W S106
750 W S111
1000 W S52
  1. Department of Public Works (1980). San Jose: Study and report on low-pressure sodium lighting. San Jose: City of San Jose. p. 8.
  2. Luginbuhl, Christian B. "Low-Pressure Sodium Issues and FAQ". Flagstaff, Arizona: U.S. Naval Observatory. Retrieved2013-12-05.
  3. Raymond Kane, Heinz Sell, Revolution in Lamps: A Chronicle of 50 Years of Progress, Second Edition, Fairmont Press, 2001. pp. 238-241.
  4. USA patent US3737717A, Arendash, Michael, "High intensity lamp containing thermal shorting fuse", published 1972-03-13, issued 1973-06-05, assigned to General Electric Co.
  5. J. J. de Groot, J. A. J. M. van Vliet, The High-Pressure Sodium Lamp, Macmillan International Higher Education, 1986, ISBN 1349091960. pp. 13-17.
  6. "SLI/H Sodium". Lamptech.co.uk. Retrieved2012-03-03.
  7. "SO/H Sodium". Lamptech.co.uk. Retrieved2012-03-03.
  8. "SOI/H Sodium". Lamptech.co.uk. Retrieved2012-03-03.
  9. "SOX Sodium". Lamptech.co.uk. Retrieved2012-03-03.
  10. "Philips MASTER SOX-E 131W BY22d 1SL/6 low pressure sodium lamp product leaflet".[dead link]
  11. "Mesoptic Street Lighting Demonstration and Evaluation Final Report"(PDF). Lighting research Center, Rensselaer Polytechnic Institute. January 31, 2008. Retrieved2011-08-29. (Comparison is with HPS and MH lamps)
  12. "HEADS UP! PHILIPS LOW PRESSURE SODIUM SOX BULBS ARE GOING THE WAY OF THE DODO". 28 September 2017.
  13. "End of an era as remaining 70 jobs at former Philips factory are to be axed". 11 July 2019.
  14. "Archived copy"(PDF). Archived from the original(PDF) on 2012-05-15. Retrieved2012-10-14.CS1 maint: archived copy as title (link)
  15. "Flagstaff Lighting Code"(PDF). Archived from the original(PDF) on 13 September 2014. Retrieved14 April 2014.
  16. Luginbuhl, C. B. (12–16 July 1999), "Why Astronomy Needs Low-Pressure Sodium Lighting", in R. J. Cohen; W. T. Sullivan (eds.), Why Astronomy Needs Low-Pressure Sodium Lighting, Preserving the Astronomical Sky, Proceedings of IAU Symposium 196, 196, Vienna, Austria: International Astronomical Union (published 2001), p. 81, Bibcode:2001IAUS..196...81L
  17. Luginbuhl, C. B.; Boley, P. A.; Daviws, D. R. (May 2014). "The impact of light source spectral power distribution on sky glow". Journal of Quantitative Spectroscopy and Radiative Transfer. 139: 21–26. Bibcode:2014JQSRT.139...21L. doi:10.1016/j.jqsrt.2013.12.004.
  18. Aubé, M.; Roby, J.; Kocifaj, M. (5 July 2013). "Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility". PLOS ONE. 8 (7): e67798. Bibcode:2013PLoSO...867798A. doi:10.1371/journal.pone.0067798. PMC3702543. PMID 23861808.
  19. Hess, John P. (January 6, 2017). "Yellow Screen and the Revenge of the Blue Screen". Filmmaker IQ. Retrieved2019-09-08.
  20. http://www.lightingassociates.org/i/u/2127806/f/tech_sheets/high_pressure_sodium_lamps.pdf
  21. "Philips SDW-T High Pressure Sodium White SON". WebExhibits. Retrieved2007-09-24.

Sodium-vapor lamp
Sodium vapor lamp Language Watch Edit A sodium vapor lamp is a gas discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm A high pressure sodium street light in Toronto A high pressure sodium vapor lamp Two varieties of such lamps exist low pressure and high pressure Low pressure sodium lamps are highly efficient electrical light sources but their yellow light restricts applications to outdoor lighting such as street lamps where they are widely used 1 High pressure sodium lamps emit a broader spectrum of light than the low pressure lamps but they still have poorer color rendering than other types of lamps 2 Low pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night Contents 1 Development 2 Low pressure sodium 2 1 Light pollution considerations 2 2 Film special effects 3 High pressure sodium 3 1 White SON expand acronym 3 2 Theory of operation 4 End of life 5 ANSI HPS ballast codes 6 See also 7 Notes 8 ReferencesDevelopment EditThe low pressure sodium arc discharge lamp was first made practical around 1920 owing to the development of a type of glass that could resist the corrosive effects of sodium vapor These operated at pressures of less than 1 Pa and produced a near monochromatic light spectrum around the sodium emission lines at 589 0 and 589 56 nanometres wavelength The yellow light produced by these limited the range of applications to those where color vision was not required 3 Research into high pressure sodium lamps occurred in both the UK and the US Increasing the pressure of the sodium vapor broadened the sodium emission spectrum so that the light produced had more energy emitted at wavelengths above and below the 589 nm region The quartz material used in mercury discharge lamps was corroded by high pressure sodium vapor A laboratory demonstration of a high pressure lamp was carried out in 1959 The development by General Electric of a sintered aluminum oxide material with magnesium oxide added to improve light transmission was an important step in construction of a commercial lamp The material was available in the form of tubing by 1962 but additional techniques were required to seal the tubes and add the necessary electrodes the material could not be fused like quartz The end caps of the arc tube would get as hot as 800 degrees C in operation then cool to room temperature when the lamp was turned off so the electrode terminations and arc tube seal had to tolerate repeated temperature cycles This problem was solved by Michael Arendash 4 at the GE Nela Park plant The first commercial high pressure sodium lamps were available in 1965 from companies in the United States the United Kingdom and the Netherlands at introduction a 400 watt lamp would produce around 100 lumens per watt 3 5 Single crystal artificial sapphire tubes were also manufactured and used for HPS lamps in the early 1970s with a slight improvement in efficacy but production costs were higher than for polycrystalline alumina tubes 3 Low pressure sodium Edit An unlit 35 W LPS SOX lamp Warm up phases of a LPS lamp The faint pink light of the Penning mixture is gradually replaced by the bright monochromatic orange light of the metallic sodium vapor A running 35 W LPS SOX lamp Spectrum of a low pressure sodium lamp The intense yellow band is the atomic sodium D line emission comprising about 90 of the visible light emission for this lamp type Two Honda Fits under low pressure sodium lamps Both appear black even though the car on the left is bright red while the car on the right is actually black Low pressure sodium LPS lamps have a borosilicate glass gas discharge tube arc tube containing solid sodium and a small amount of neon and argon gas in a Penning mixture to start the gas discharge The discharge tube may be linear SLI lamp 6 or U shaped When the lamp is first started it emits a dim red pink light to warm the sodium metal within a few minutes as the sodium metal vaporizes the emission becomes the common bright yellow These lamps produce a virtually monochromatic light averaging a 589 3 nm wavelength actually two dominant spectral lines very close together at 589 0 and 589 6 nm The colors of objects illuminated by only this narrow bandwidth are difficult to distinguish LPS lamps have an outer glass vacuum envelope around the inner discharge tube for thermal insulation which improves their efficiency Earlier LPS lamps had a detachable dewar jacket SO lamps 7 Lamps with a permanent vacuum envelope SOI lamps were developed to improve thermal insulation 8 Further improvement was attained by coating the glass envelope with an infrared reflecting layer of indium tin oxide resulting in SOX lamps 9 LPS lamps are among the most efficient electrical light sources when measured in photopic lighting conditions producing above 100 and up to 206 lm W 10 This high efficiency is partly due to the light emitted being at a wavelength near the peak sensitivity of the human eye They are used mainly for outdoor lighting such as street lights and security lighting where faithful color rendition is not important Recent studies show that under typical nighttime mesopic driving conditions whiter light can provide better results at a lower level of illumination 11 LPS lamps are similar to fluorescent lamps in that they are a low intensity light source with a linear lamp shape They do not exhibit a bright arc as do High intensity discharge HID lamps they emit a softer luminous glow resulting in less glare Unlike HID lamps during a voltage dip low pressure sodium lamps return to full brightness rapidly LPS lamps are available with power ratings from 10 W up to 180 W longer lamp lengths can however suffer design and engineering problems Modern LPS lamps have a service life of about 18 000 hours and do not decline in lumen output with age though they do increase in energy consumption by about 10 towards end of life This property contrasts with mercury vapor HID lamps which become dimmer towards the end of life to the point of being ineffective while consuming undiminished electrical power In 2017 Philips Lighting the last manufacturer of LPS lamps announced they were discontinuing production of the lamps due to falling demand 12 Initially production was due to be phased out in the course of 2020 however this date was brought forward and the last lamps were produced at the Hamilton factory in November 2019 13 Light pollution considerations Edit For locations where light pollution is a consideration such as near astronomical observatories or sea turtle nesting beaches low pressure sodium is preferred as formerly in San Jose and Flagstaff Arizona 14 15 Such lamps emit light on just two dominant spectral lines with other much weaker lines and therefore have the least spectral interference with astronomical observation 16 Now that production of LPS lamps has ceased consideration is being given into the use of narrow band amber LEDs which are on a similar color spectrum to LPS The yellow color of low pressure sodium lamps also leads to the least visual sky glow due primarily to the Purkinje shift of dark adapted human vision causing the eye to be relatively insensitive to the yellow light scattered at low luminance levels in the clear atmosphere 17 18 One consequence of widespread public lighting is that on cloudy nights cities with enough lighting are illuminated by light reflected off the clouds Where sodium vapor lights are the source of urban illumination the night sky is tinged with orange Film special effects Edit Sodium vapor process occasionally referred to as yellowscreen is a film technique that relies on narrowband characteristics of LPS lamp Color negative film is typically not sensitive to the yellow light from an LPS lamp but special black and white film is able to record it Using a special camera scenes are recorded on two spools simultaneously one with actors or other foreground objects and another that becomes a mask for later combination with different background This technique originally yielded results superior to blue screen technology and was used in years 1956 to 1990 mostly by Disney Studios Notable examples of films using this technique include Alfred Hitchcock s The Birds and the Disney films Mary Poppins and Bedknobs and Broomsticks Later advancements in blue and green screen techniques and computer imagery closed that gap leaving SVP economically impractical 19 High pressure sodium Edit High pressure sodium lamp in operation Spectrum of high pressure sodium lamp The yellow red band on the left is the atomic sodium D line emission the turquoise line is a sodium line that is otherwise quite weak in a low pressure discharge but becomes intense in a high pressure discharge Most of the other green blue and violet lines arise from mercury Diagram showing the spectral output of a typical high pressure sodium HPS lamp Office building illuminated by high pressure sodium lamps High pressure sodium lamp Philips SON T Master 600 W High pressure sodium HPS lamps have been widely used in industrial lighting especially in large manufacturing facilities and are commonly used as plant grow lights They contain mercury 20 They have also been widely used for outdoor area lighting such as on roadways parking lots and security areas Understanding the change in human color vision sensitivity from photopic to mesopic and scotopic is essential for proper planning when designing lighting for roadways 11 High pressure sodium lamps are quite efficient about 100 lumens per watt when measured for photopic lighting conditions Some higher power lamps e g 600 watt have efficacies of about 150 lumens per watt Since the high pressure sodium arc is extremely chemically reactive the arc tube is typically made of translucent aluminum oxide This construction led the General Electric Company to use the tradename Lucalox for its line of high pressure sodium lamps Xenon at a low pressure is used as a starter gas in the HPS lamp It has the lowest thermal conductivity and lowest ionization potential of all the stable noble gases As a noble gas it does not interfere with the chemical reactions occurring in the operating lamp The low thermal conductivity minimizes thermal losses in the lamp while in the operating state and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state which allows the lamp to be easily started White SON expand acronym Edit A variation of the high pressure sodium introduced in 1986 the White SON has a higher pressure than the typical HPS SON lamp producing a color temperature of around 2700 kelvins with a color rendering index CRI of about 85 greatly resembling the color of an incandescent light 21 These lamps are often used indoors in cafes and restaurants for aesthetic effect However white SON lamps have higher cost shorter service lives and lower light efficiency and so they cannot compete with HPS at this time Theory of operation Edit This section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed December 2017 Learn how and when to remove this template message Diagram of a high pressure sodium lamp An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor that is needed to draw an arc The temperature of the amalgam is determined to a great extent by lamp power The higher the lamp power the higher will be the amalgam temperature The higher the temperature of the amalgam the higher will be the mercury and sodium vapor pressures in the lamp and the higher will be the terminal voltage As the temperature rises the constant current and increasing voltage consumes increasing energy until the operating level of power is reached For a given voltage there are generally three modes of operation The lamp is extinguished and no current flows The lamp is operating with liquid amalgam in the tube The lamp is operating with all amalgam evaporated The first and last states are stable because the lamp resistance is weakly related to the voltage but the second state is unstable Any anomalous increase in current will cause an increase in power causing an increase in amalgam temperature which will cause a decrease in resistance which will cause a further increase in current This will create a runaway effect and the lamp will jump to the high current state 3 Because actual lamps are not designed to handle this much power this would result in catastrophic failure Similarly an anomalous drop in current will drive the lamp to extinction It is the second state that is the desired operating state of the lamp because a slow loss of the amalgam over time from a reservoir will have less effect on the characteristics of the lamp than a fully evaporated amalgam The result is an average lamp life in excess of 20 000 hours In practical use the lamp is powered by an AC voltage source in series with an inductive ballast in order to supply a nearly constant current to the lamp rather than a constant voltage thus assuring stable operation The ballast is usually inductive rather than simply being resistive to minimize energy waste from resistance losses Because the lamp effectively extinguishes at each zero current point in the AC cycle the inductive ballast assists in the reignition by providing a voltage spike at the zero current point The light from the lamp consists of atomic emission lines of mercury and sodium but is dominated by the sodium D line emission This line is extremely pressure resonance broadened and is also self reversed because of absorption in the cooler outer layers of the arc giving the lamp its improved color rendering characteristics In addition the red wing of the D line emission is further pressure broadened by the Van der Waals forces from the mercury atoms in the arc End of life EditThis section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed December 2017 Learn how and when to remove this template message Sodium vapor street light Closeup after dark At end of life high pressure sodium HPS lamps exhibit a phenomenon known as cycling caused by a loss of sodium in the arc Sodium is a highly reactive element and is lost in a reaction with the aluminum oxide of the arc tube The products are sodium oxide and aluminum 6 Na Al2O3 3 Na2O 2 Al As a result these lamps can be started at a relatively low voltage but as they heat up during operation the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge As a lamp gets older the maintaining voltage for the arc eventually rises to exceed the maximum voltage output by the electrical ballast As the lamp heats to this point the arc fails and the lamp goes out Eventually with the arc extinguished the lamp cools down again the gas pressure in the arc tube is reduced and the ballast can once again cause the arc to strike The effect of this is that the lamp glows for a while and then goes out typically starting at a pure or bluish white then moving to a red orange before going out More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles as the repeated high voltage ignitions needed to restart the arc reduce the lifetime of the ballast If power is removed and reapplied the ballast will make a new series of startup attempts LPS lamp failure does not result in cycling rather the lamp will simply not strike or will maintain the dull red glow of the start up phase In another failure mode a tiny puncture of the arc tube leaks some of the sodium vapor into the outer vacuum bulb The sodium condenses and creates a mirror on the outer glass partially obscuring the arc tube The lamp often continues operating normally but much of the light generated is obscured by the sodium coating providing no illumination ANSI HPS ballast codes EditPower output ANSI codes35 W S7650 W S6870 W S62100 W S54150 W S55 55v or S56 100v 200 W S66250 W S50310 W S67400 W S51600 W S106750 W S1111000 W S52See also EditArc lamp High intensity discharge lamp HID History of street lighting in the United States List of light sources Metal halide lamp Mercury vapor lamp Neon lamp Street light Sulfur lamp Light pollutionNotes Edit Department of Public Works 1980 San Jose Study and report on low pressure sodium lighting San Jose City of San Jose p 8 Luginbuhl Christian B Low Pressure Sodium Issues and FAQ Flagstaff Arizona U S Naval Observatory Retrieved 2013 12 05 a b c Raymond Kane Heinz Sell Revolution in Lamps A Chronicle of 50 Years of Progress Second Edition Fairmont Press 2001 pp 238 241 USA patent US3737717A Arendash Michael High intensity lamp containing thermal shorting fuse published 1972 03 13 issued 1973 06 05 assigned to General Electric Co J J de Groot J A J M van Vliet The High Pressure Sodium Lamp Macmillan International Higher Education 1986 ISBN 1349091960 pp 13 17 SLI H Sodium Lamptech co uk Retrieved 2012 03 03 SO H Sodium Lamptech co uk Retrieved 2012 03 03 SOI H Sodium Lamptech co uk Retrieved 2012 03 03 SOX Sodium Lamptech co uk Retrieved 2012 03 03 Philips MASTER SOX E 131W BY22d 1SL 6 low pressure sodium lamp product leaflet dead link a b Mesoptic Street Lighting Demonstration and Evaluation Final Report PDF Lighting research Center Rensselaer Polytechnic Institute January 31 2008 Retrieved 2011 08 29 Comparison is with HPS and MH lamps HEADS UP PHILIPS LOW PRESSURE SODIUM SOX BULBS ARE GOING THE WAY OF THE DODO 28 September 2017 End of an era as remaining 70 jobs at former Philips factory are to be axed 11 July 2019 Archived copy PDF Archived from the original PDF on 2012 05 15 Retrieved 2012 10 14 CS1 maint archived copy as title link Flagstaff Lighting Code PDF Archived from the original PDF on 13 September 2014 Retrieved 14 April 2014 Luginbuhl C B 12 16 July 1999 Why Astronomy Needs Low Pressure Sodium Lighting in R J Cohen W T Sullivan eds Why Astronomy Needs Low Pressure Sodium Lighting Preserving the Astronomical Sky Proceedings of IAU Symposium 196 196 Vienna Austria International Astronomical Union published 2001 p 81 Bibcode 2001IAUS 196 81L Luginbuhl C B Boley P A Daviws D R May 2014 The impact of light source spectral power distribution on sky glow Journal of Quantitative Spectroscopy and Radiative Transfer 139 21 26 Bibcode 2014JQSRT 139 21L doi 10 1016 j jqsrt 2013 12 004 Aube M Roby J Kocifaj M 5 July 2013 Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression Photosynthesis and Star Visibility PLOS ONE 8 7 e67798 Bibcode 2013PLoSO 867798A doi 10 1371 journal pone 0067798 PMC 3702543 PMID 23861808 Hess John P January 6 2017 Yellow Screen and the Revenge of the Blue Screen Filmmaker IQ Retrieved 2019 09 08 http www lightingassociates org i u 2127806 f tech sheets high pressure sodium lamps pdf Philips SDW T High Pressure Sodium White SON WebExhibits Retrieved 2007 09 24 References Editde Groot J J van Vliet J A J M 1986 The High Pressure Sodium Lamp Deventer Kluwer Technische Boeken BV ISBN 978 90 201 1902 2 OCLC 16637733 Waymouth John F 1971 Electric Discharge Lamps Cambridge MA MIT Press ISBN 978 0 262 23048 3 OCLC 214331 Museum of Electric Discharge Lamps USA patent US3737717A Arendash Michael High intensity lamp containing thermal shorting fuse published 1972 03 13 issued 1973 06 05 assigned to General Electric Co Retrieved from https en wikipedia org w index php title Sodium vapor lamp amp oldid 1047100186, wikipedia, wiki, book,

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