Jump to content

LED lamp

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by Gerfriedc (talk | contribs) at 07:52, 16 September 2012 (→Application). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
An assortment of LED lightbulbs commercially available as of 2010 as replacements for screw-in bulbs, including floodlight fixtures (left), reading light (center), household lamps (center right and bottom), and low-power accent light (right) applications.
A 17W tube of LEDs which has the same intensity as a 45W fluorescent tube
LED spotlight using 60 individual diodes for mains voltage power

An LED lamp (or LED light bulb) is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. LED lamps offer long service life and high energy efficiency, but initial costs are higher than those of fluorescent and incandescent lamps. Chemical decomposition of LED chips reduces luminous flux over life cycle as with conventional lamps.

The LEDs involved may be conventional semiconductor light-emitting diodes, organic LEDs (OLED), or polymer light-emitting diodes (PLED) devices. However, PLED technologies are not commercially available. Diode technology improves steadily.

LED lamps can be made interchangeable with other types of lamps. Assemblies of high power light-emitting diodes can be used to replace incandescent or fluorescent lamps. Some LED lamps are made with identical bases so that they are directly interchangeable with incandescent bulbs. Since the luminous efficacy (amount of visible light produced per unit of electrical power input) varies widely between LED and incandescent lamps, lamps are usefully marked with their lumen output to allow comparison with other types of lamps. LED lamps are sometimes marked to show the watt rating of an incandescent lamp with approximately the same lumen output, for consumer reference in purchasing a lamp that will provide a similar level of illumination.

Efficiency of LED devices continues to improve, with some chips able to emit more than 100 lumens per watt. LEDs do not emit light in all directions, and their directional characteristics affect the design of lamps. The efficiency of conversion from electric power to light is generally higher than with incandescent lamps. Since the light output of many types of light-emitting diodes is small compared to incandescent and compact fluorescent lamps, in most applications multiple diodes are assembled.

Diodes use direct current (DC) electrical power. To use them from standard AC power they are operated with internal or external rectifier circuits that provide a regulated current output at low voltage. LEDs are degraded or damaged by operating at high temperatures, so LED lamps typically include heat dissipation elements such as heat sinks and cooling fins.

Technology overview

Dropped ceiling with LED lamps

General-purpose lighting needs white light. LEDs emit light in a very small band of wavelengths, emitting light of a color characteristic of the energy bandgap of the semiconductor material used to make the LED. To emit white light from LEDs requires either mixing light from red, green, and blue LEDs, or using a phosphor to convert some of the light to other colors.

The first method (RGB- or trichromatic white LEDs) uses multiple LED chips, each emitting a different wavelength, in close proximity to generate the broad spectrum of white light. The advantage of this method is that the intensity of each LED can be adjusted to "tune" the character of the light emitted. The major disadvantage is high production cost. The character of the light can be changed dynamically by adjusting the power supplied to the different LEDs.

The color rendering of RGB LEDs, however, is worse than one would expect; the wavelength gap between red and green is much larger than that between green and blue, resulting in an uneven spectral density. An orange fruit, for example, does reflect some red and it does reflect some green, but not in a ratio that the human retina interprets as orange. Neglecting to poll the orange line makes most orange objects appear reddish. RGB LEDs are therefore suitable for display purposes, but less so for illumination, which prompted some manufacterers to add a fourth, amber LED, marketing the product as RGBA LED (not to be confused with the RGBA color space) or tetrachromatic white LED. It can be expected that the number of colors will be further increased to six or more, equally-tempered wavelengths.

The second method, phosphor converted LEDs (pcLEDs) uses one short-wavelength LED (usually blue, sometimes ultraviolet) in combination with a phosphor which absorbs a portion of the blue light and emits a broader spectrum of white light. (The same mechanism—the Stokes shift—is used in a fluorescent lamp emitting white light from a UV-illuminated phosphor.) The major advantage is the low production cost. The CRI (color rendering index) value can range from less than 70 to over 90, and color temperatures in the range of 2700 K (matching incandescent lamps) up to 7000 K are available. The character of the light cannot be changed dynamically. The phosphor conversion absorbs some energy, but most of the electrical energy is still wasted as heat within the LED chip itself. The low cost and adequate performance makes this the most widely used LED technology for general lighting today.

A single LED is a low-voltage solid-state device and cannot be directly operated on standard high-voltage AC power without circuitry to control the current flow through the lamp. In principle a series diode and resistor could be used to limit the current and to control its direction, but this would be very inefficient since most of the applied power would be dissipated by the resistor. A series string of LEDs would minimize dropped-voltage losses, but one LED failure would extinguish the whole string. Paralleled strings increase reliability by providing redundancy. In practice, three or more strings are usually used. To be useful for illumination, a number of LEDs must be placed close together in a lamp to combine their illuminating effects. As of 2012, white LED assemblies emitting 10,000 lm are available. When using the color-mixing method, a uniform color distribution can be difficult to achieve, while the arrangement of white LEDs is not critical for color balance. Further, degradation of different LEDs at various times in a color-mixed lamp can lead to an uneven color output. LED lamps usually consist of clusters of LEDs in a housing with driver electronics, a heat sink, and optics.

Application

The main difference to other light sources is the directed light. Thus illuminating a flat defined area requires less Lumen compared to light sources which would need reflectors or lenses to do the same. For illuminating an 360° orbit, the benefits of LED are much smaller. LED lamps are used for both general and special-purpose lighting. Where colored light is needed, LEDs naturally emitting many colors are available, with no need for filters. This improves the energy efficiency over a white light source that generates all colors of light then discards some of the visible energy in a filter.

BAPS Shri Swaminarayan Mandir Atlanta Illumination with color mixing LED fixtures.

Compared to fluorescent bulbs, introduced at the 1939 World's Fair, advantages claimed for LED light bulbs are that they contain no mercury (unlike a Compact fluorescent lamp or CFL), that they turn on instantly, and that lifetime is unaffected by cycling on and off, so that they are well suited for light fixtures where bulbs are often turned on and off. LED light bulbs are also mechanically robust; most other artificial light sources are fragile.

White-light light-emitting diode lamps have longer life expectancy and higher efficiency (the same light for less electricity) than most other lighting. LED sources are compact, which gives flexibility in designing lighting fixtures and good control over the distribution of light with small reflectors or lenses. Because of the small size of LEDs, control of the spatial distribution of illumination is extremely flexible,[1] and the light output and spatial distribution of a LED array can be controlled with no efficiency loss.

LED lamps have no glass tubes to break, and their internal parts are rigidly supported, making them resistant to vibration and impact. With proper driver electronics design, an LED lamp can be made dimmable over a wide range; there is no minimum current needed to sustain lamp operation.

LEDs using the color-mixing principle can emit a wide range of colors by changing the proportions of light generated in each primary color. This allows full color mixing in lamps with LEDs of different colors.[2] In contrast to other lighting technologies, LED emission tends to be directional (or at least lambertian). This can be either an advantage or a disadvantage, depending on requirements. For applications where non-directional light is required, either a diffuser is used, or multiple individual LED emitters are used to emit in different directions.

Household LED lamps

LED lamps
  • LED Lamp with E27 Edison screw, interchangeable with incandescent lamps
    LED Lamp with E27 Edison screw, interchangeable with incandescent lamps
  • Top view of a Philips 12.5 W LED lamp, interchangeable with a 60 watt incandescent lamp
    Top view of a Philips 12.5 W LED lamp, interchangeable with a 60 watt incandescent lamp
  • LED spotlight using 38 individual diodes for mains voltage power
    LED spotlight using 38 individual diodes for mains voltage power
  • LED tubes in various lengths
    LED tubes in various lengths
  • LED lamp with GU5.3 base and aluminum heat sink, intended to replace halogen reflector lamps
    LED lamp with GU5.3 base and aluminum heat sink, intended to replace halogen reflector lamps

Lamp sizes and bases

LED lamps intended to be interchangeable with incandescent lamps are made in standard light bulb shapes, such as an Edison screw base, an MR16 shape with a bi-pin base, or a GU5.3 (Bipin cap) or GU10 (bayonet socket) and are made compatible with the voltage supplied to the sockets. LED lamps include circuitry to rectify the AC power and to convert the voltage to a level usable by the LED.

LED light bulbs

LED lamps are made that replace screw-in incandescent or compact fluorescent light bulbs. Most LED lamps replace incandescent bulbs rated from 5 to 60 watts. As of 2010, some LED lamps replace higher wattage bulbs; For example, one manufacturer claims a 16-watt LED bulb as bright as a 150W halogen lamp.[3] A standard general-purpose incandescent bulb emits light at an efficiency of about 14 to 17 lumens/W depending on its size and voltage. According to the European Union standard, an energy-efficient bulb that claims to be the equivalent of a 60W tungsten bulb must have a minimum light output of 806 lumens.[4]

A selection of consumer LED bulbs available as drop-in replacements for incandescent bulbs in screw-type sockets

Some models of LED bulbs work with dimmers as used for incandescent lamps. LED lamps often have directional light characteristics. The lamps have declined in cost to between US$10 to $50 each as of 2012. These bulbs are more power-efficient than compact fluorescent bulbs[5] and offer lifespans of 30,000 or more hours, reduced if operated at a higher temperature than specified. Incandescent bulbs have a typical life of 1,000 hours, compact fluorescents about 8,000 hours.[citation needed] The bulbs maintain output light intensity well over their life-times. Energy Star specifications require the bulbs to typically drop less than 10% after 6000 or more hours of operation, and in the worst case not more than 15%.[6] They are also mercury-free, unlike fluorescent lamps. LED lamps are available with a variety of color properties. The higher purchase cost than other types may be more than offset by savings in energy and maintenance.[7]

Several companies offer LED lamps for general lighting purposes. The technology is improving rapidly and new energy-efficient consumer LED lamps are available.[8]

Specialty uses

LED Flashlight replacement bulb (left), with tungsten equivalent (right)

White LED lamps have achieved market dominance in applications where high efficiency is important at low power levels. Some of these applications include flashlights, solar-powered garden or walkway lights, and bicycle lights. Monochromatic (colored) LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright monochromatic light is a desired feature, and in strings of holiday lights.

LED lights have also become very popular in gardening and agriculture by 2010. First used by NASA to grow plants in space, LEDs came into use for home and commercial applications for indoor horticulture (aka grow lights). The wavelengths of light emitted from LED lamps have been specifically tailored to supply light in the spectral range needed for chlorophyll absorption in plants, promoting growth while reducing wastage of energy by emitting minimal light at wavelengths that plants do not require. The red and blue wavelengths of the visible light spectrum are used for photosynthesis, so these are the colors almost always used in LED grow light panels.

Pioneering mass use

In 2008 Sentry Equipment Corporation in Oconomowoc, Wisconsin, USA, was able to light its new factory interior and exterior almost solely with LEDs. Initial cost was three times more than a traditional mix of incandescent and fluorescent lamps, but the extra cost will be repaid within two years via electricity savings, and the lamps should not need replacing for 20 years.[9] In 2009, the Manapakkam, Chennai office of the Indian IT company iGate spent ₹3,700,000 (US$80,000) to light 57,000 sq ft (5,300 m2) of office space with LEDs. The firm expects the new lighting to pay for itself fully within 5 years.[10]

LEDs as Christmas illumination in Viborg, Denmark.

In 2009 the exceptionally big Christmas tree standing in front of the Turku Cathedral in Finland was hung with 710 LED bulbs, each using 2 watts. It has been calculated that these LED lamps will pay for themselves in three and a half years, even though the lights run for only 48 days per year.[11]

In 2009 a new highway (A29) was inaugurated in Aveiro, Portugal, it included the first European public LED-based lighting highway[12]

By 2010 mass installations of LED lighting for commercial and public uses were becoming common. LED lamps have also been used for a number of demonstration projects for outdoor lighting and LED street lights. The United States Department of Energy has available several reports on the results of many pilot projects for municipal outdoor lighting.[13] Many additional streetlight and municipal outdoor lighting projects have been announced.[14]

Comparison to other lighting technologies

See luminous efficacy for an efficiency chart comparing various technologies.

  • Incandescent lamps (light bulbs) generate light by passing electric current through a resistive filament, thereby heating the filament to a very high temperature so that it glows and emits visible light. A broad range of visible frequencies are naturally produced, yielding a "warm" yellow or white color quality. Incandescent light is highly inefficient, as about 98% of the energy input is emitted as heat.[15] A 100 W light bulb for 120 V operation emits about 1,700 lumens, about 17 lumens/W; for 230 V bulbs the figures are 1200 lm and 12 lm/W. Incandescent lamps are relatively inexpensive to make. The typical lifespan of an AC incandescent lamp is around 1,000 hours.[16] They work well with dimmers. Most older light fixtures are designed for the size and shape of these traditional bulbs.
  • Fluorescent lamps (light bulbs) work by passing electricity through mercury vapor, which in turn emits ultraviolet light. The ultraviolet light is then absorbed by a phosphor coating inside the lamp, causing it to glow, or fluoresce. While the heat generated by a fluorescent lamp is much less than its incandescent counterpart, energy is still lost in generating the ultraviolet light and converting this light into visible light. If the lamp breaks, exposure to mercury can occur. Linear fluorescent lamps are typically five to six times the cost of equivalent incandescent lamps but have life spans around 10,000 and 20,000 hours. Lifetime varies from 1,200 hours to 20,000 hours for compact fluorescent lamps. Most fluorescent lamps are not compatible with dimmers. Those with "iron" ballasts flicker at 100 or 120 Hz, and are less efficient.[citation needed] The latest T8-sized triphosphate fluorescent lamps made by Osram, Philips, Crompton and others have a life expectancy greater than 50,000 hours, if coupled with a warm-start electronic ballast. The life expectancy depends on the number of on/off cycles, and is lower if the light is cycled often. The efficiency of these new lamps approaches 100 lumens/W.[citation needed] The efficiency of fluorescent tubes with modern electronic ballasts and compact fluorescents commonly ranges from 50 to 67 lumens/W. For comparison, general household LED bulbs available in 2011 emit 64 lumens/W,[17] with the best LED bulbs coming in at about 100 lumens/W.[18]
Cost Comparison
Incandescent Halogen Fluorescent LED (Generic) LED (Philips) LED (Philips L-Prize)
Purchase price $0.41[19] $4[20] $4[21] $20[18] $25[22] $50[23]
Electricity usage 60 W 42 W 13 W 9 W 12.5 W 10 W
Lumens 860 570 660[24] 900 800 940
Lumens/Watt 14.3 13.6 50.8 100 64 94
Color Temperature Kelvin 2700 3100[25] 2700 3000 2700 2700
CRI 100 100 82 >75[26] 85 92
Lifespan (hours) 2,000 3,500 8,000 25,000 25,000 30,000
Bulb cost over 10 years – @6hours/day $4.49 $25.03 $10.95 $17.52 $21.90 $36.50
Energy cost over 10 years – @15cents/kWhr $197.10 $137.97 $42.71 $29.57 $41.06 $32.85
Total $201.59 $163.00 $53.66 $47.09 $62.96 $69.35
Comparison based on 6 hours use per day (21,900 hours over 10 yrs)

Research and development

US Department of Energy

Comparison of Philips LED bulbs intended as screw-in replacements for the 60-W incandescent bulb. The original Philips A-19 "Endura LED" bulb is on the left, and the L-Prize bulb on the right.

In May 2008, the U. S. Department of Energy (DOE) announced details of the Bright Tomorrow Lighting Prize competition, known as the "L Prize". This is the first government-sponsored technology competition designed to spur lighting producers to develop high quality, high efficiency solid-state lighting products to replace the common light bulb. The competition will award cash prizes, and may also lead to opportunities for federal purchasing agreements, utility programs, and other incentives for winning products.

The Energy Independence and Security Act (EISA) of 2007 authorized the DOE to establish the Bright Tomorrow Lighting Prize competition. The legislation challenges industry to develop replacement technologies for the most commonly used and inefficient products, 60 W incandescent lamps and PAR 38 halogen lamps. The L Prize specifies technical requirements for these two competition categories. Lighting products meeting the competition requirements would use just 17% of the energy used by most incandescent lamps in use today. A future L Prize program announcement will call for developing a new “21st Century Lamp,” as authorized in the legislation.

The EISA legislation establishes basic requirements and prize amounts for each category. The legislation authorizes up to $20 million in cash prizes.[27] On September 24, 2009 the DOE announced that Philips Lighting North America was the first to submit lamps in the category to replace the standard 60 W A-19 "Edison screw fixture" light bulb,[7] with a design based on their earlier "EnduraLED" consumer product. On August 3, 2011, DOE awarded the prize in the 60 W replacement category to Philips bulb after 18 months of extensive testing.[28] The same day, CREE demonstrated a prototype lamp producing 1330 lumens with a mere 8.7 W of input power.[29] While the CREE lamp has not undergone DOE reliability testing and no commercial release date was promised, it is an indication that the "21st Century Lamp" performance levels may soon be within reach of commercial products.

The 10-W, 900-lumen Philips bulb was made available to consumers in April 2012.[30]

National Institute of Standards and Technology

In June 2008, scientists at the National Institute of Standards and Technology (NIST) announced the first two standards for solid-state lighting in the United States. These standards detail the color specifications of LED lamps and LED light fixtures, and the test methods that producers should use when testing these solid-state lighting products for total light output, energy use, and chromaticity or color quality.

The Illuminating Engineering Society of North America (IESNA) published a documentary standard LM-79, which describes the methods for testing solid-state lighting products for their light output (lumens), energy efficiency (lumens per watt) and chromaticity.

The solid-state lights being studied are intended for general illumination, but white lights used today vary greatly in chromaticity, or specific shade of white. The American National Standards Institute (ANSI) published the standard C78.377-2008, which specifies the recommended color ranges for solid-state lighting products using cool to warm white LEDs with various correlated color temperatures.[31]

DOE launched the Energy Star program for solid-state lighting products in 2008. NIST scientists assisted DOE by providing research, technical details and comments for the Energy Star specifications. Energy Star certification assures consumers that products save energy and are high quality and also serves as an incentive for producers to provide energy-saving products for consumers.

Environmental Protection Agency

In the United States and Canada, the Energy Star program since 2008 labels lamps that meet a set of standards for starting time, life expectancy, color, and consistency of performance. The intent of the program is to reduce consumer concerns due to variable quality of products, by providing transparency and standards for the labeling and usability of products available in the market.[32] Energy Star Light Bulbs for Consumers is a resource for finding and comparing Energy Star qualified lamps.

Other venues

In the United Kingdom a program is run by the Energy Saving Trust to identify lighting products that meet energy conservation and performance guidelines.[33]

Philips Lighting has ceased research on compact fluorescents, and is devoting the bulk of its research and development budget, 5 percent of the company's global lighting revenue, to solid-state lighting.[9]

In January 2009, it was reported that researchers at Cambridge University had developed an LED bulb that costs £2 (about $3 U.S.), is 12 times as energy efficient as a tungsten bulb, and lasts for 100,000 hours.[34] Honeywell Electrical Devices and Systems (ED&S) recommend world wide usage of LED lighting as it is energy efficient and can help save the Climate.[35]

Remaining problems

The production process of white LEDs is complex and many aspects have room for improvement. This means that the production price of volume products is still relatively high compared to traditional light sources. The process used to deposit the active semiconductor layers of the LED is constantly improved to increase yields and production. The phosphors, which are needed for their ability to emit a broader wavelength spectrum of light, problems tuning the absorption and emission, and inflexibility of form have been issues.[citation needed]

More apparent to the end user, however, is the color rendering index (CRI) of low quality LEDs. CRI measures a light source's ability to render colors, with 100 being the maximum. LEDs with CRI below 75 are not recommended use in indoor lighting.[36] Better CRI LEDs are more expensive, and more research and development is needed to reduce costs.

LEDs also have limited temperature tolerance and falling efficiency as component temperature rises. This limits the total LED power that can practically be fitted into lamps that physically replace existing filament and compact fluorescent types. Much research and development is invested in improving thermal traits. Thermal management of high-power LEDs is a significant factor in design of solid state lighting equipment.

The long life of solid-state lighting products, expected to be about 50 times the most common incandescent bulbs, poses a problem for bulb makers, whose current customers buy frequent replacements.[9]

Some critics assert that producers may over-represent the efficiency and traits of their products to sell into a rapidly growing marketplace, suggesting that consumers still need to be wary of claims made about products in this market.[37]

Applications

This garden light can use stored solar energy because of the low power use of its LED

See also

References

  1. ^ Ivan Moreno, Maximino Avendaño-Alejo, and Rumen I. Tzonchev (2006). "Designing light-emitting diode arrays for uniform near-field irradiance" (PDF). Applied Optics. 45 (10): 2265–2272. doi:10.1364/AO.45.002265. PMID 16607994.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ Ivan Moreno, Ulises Contreras (2007). "Color distribution from multicolor LED arrays". Optics Express. 15 (6): 3607–18. doi:10.1364/OE.15.003607. PMID 19532605.
  3. ^ Commercially available 150W Halogen Equivalent PAR38 (240V). Ledlightingsupplier.co.uk. Retrieved 2012-06-02.
  4. ^ Lonsdale, Sarah (July 7, 2010). "Green property: energy-efficient bulbs". The Daily Telegraph. London. Retrieved 2011-06-08.
  5. ^ Elisabeth Rosenthal and Felicity Barringer, "Green Promise Seen in Switch to LED Lighting," New York Times, May 29, 2009
  6. ^ "Integral LED Lamps Criteria Development" (PDF).
  7. ^ a b Taub, Eric (2009-09-24). "Build a Better Bulb for a $10 Million Prize". New York Times. Retrieved 2010-02-06. {{cite news}}: Unknown parameter |coauthor= ignored (|author= suggested) (help)
  8. ^ Eric A. Taub, "LED Bulbs for the Home Near the Marketplace," The New York Times, May 16, 2010; see also the Matthew L. Wald, New York Times Green Blog, An LED That Mimics an Old Standby, June 24, 2010,
  9. ^ a b c Fans of L.E.D.'s Say This Bulb's Time Has Come By Eric A. Taub. Published: July 28, 2008 – NY Times
  10. ^ Led'ing the way, Nitya Varadarajan, October 5, 2009
  11. ^ "Of the top six in Turku, led a move – HS.fi – Domestic". November 19, 2009. Retrieved 2012-01-09.
  12. ^ New highway connecting Lisbon to Oporto includes first European LED based lighting in a highway, Aveiro September 11, 2009
  13. ^ U. S. Department of Energy, Solid-State Lighting GATEWAY Demonstration Results (Retrieved 2010-07-16)
  14. ^ for example, Seattle: "Seattle Picked to Lead National Effort on LED Street Lights" (Retrieved 2010-07-16); Scottsdale: "LED Streetlight Installation" (Retrieved 2010-07-16); Ann Arbor: LED street lights (Retrieved 2010-07-16)
  15. ^ Keefe, T.J. (2007). "The Nature of Light". Retrieved 2009-09-10.
  16. ^ A Short History of Electric Light, The Incandescent Lamp, 1900 to 1920
  17. ^ "Philips wins Energy Star Award for 800 lumen, 12.5 Watt LED bulb" (PDF). February 11, 2011. Retrieved 2011-12-21.
  18. ^ a b "Amazon.com: LED Light Bulb, 900 Lumen, Warm White, 9 Watt (65W Replacement)". February 5, 2012. Retrieved 2012-02-05.
  19. ^ "HomeDepot.com: Philips 60-Watt Household Incandescent Light Bulb". Retrieved 2012-07-26.
  20. ^ "Amazon.com: 42-Watt Halogen : Home Improvement". November 28, 2007. Retrieved 2012-02-05.
  21. ^ "Amazon.com: GE 74198 13-Watt Energy Smart CFL Light Bulb : Home Improvement". November 28, 2007. Retrieved 2012-02-05.
  22. ^ "Amazon.com: Philips 409904 / 423343 Dimmable AmbientLED 12.5-Watt A19 Light Bulb: Home Improvement". March 25, 2011. Retrieved 2012-04-15.
  23. ^ "GreenLightMovement.com: How Much Energy Can I Save With LED Lights?". May 31, 2012. Retrieved 2012-06-02.
  24. ^ "74198 specifications from GE".
  25. ^ 3100°K is typical; individual bulbs vary. See Temperature of a Halogen Light Bulb, The Physics Factbook, Glenn Elert, ed., (Retrieved 2012-05-12)
  26. ^ LED Light Bulb, 900 Lumen, Warm White, 9 Watt (65W Replacement), Clearance Sale : LED Bulbs. G7power.com. Retrieved 2012-06-02.
  27. ^ Progress Alerts – 2010, US Department of Energy
  28. ^ Department of Energy Announces Philips Lighting North America as Winner of L Prize Competition | Department of Energy. Energy.gov (2011-08-03). Retrieved 2012-06-02.
  29. ^ "Cree Prototype Exceeds DOE's 21st Century Lamp L PrizeSM Requirements". August 1, 2011. Retrieved 2012-01-09.
  30. ^ Cangeloso, Sal (April 18, 2012). "Philips' L Prize bulb is efficient, expensive, and available". Retrieved 2012-05-12.
  31. ^ American National Standard for Specifications for the Chromaticity of Solid-State Lighting (SSL) Products. Nema.org. Retrieved 2012-06-02.
  32. ^ Energy Star Program Requirements for CFLS Partner Commitments, 4th edition, dated 03/07/08, retrieved 2008-06-25.
  33. ^ Energy saving lightbulbs. Energysavingtrust.org.uk. Retrieved 2012-06-02.
  34. ^ Great bright hope to end battle of the light bulbs, The Daily Mail, January 29, 2009
  35. ^ "Switching to LED is a global task: Honeywell". 07 June 2012. {{cite news}}: Check date values in: |date= (help)
  36. ^ ENERGY STAR Program Requirements for Solid State Lighting Luminaires. (PDF) . Retrieved 2012-06-02.
  37. ^ Justin Maeers, LED misrepresentations, May 2010

Further reading

Wikimedia Commons has media related to LED lamps.

Template:Link GA

Retrieved from "https://en.wikipedia.org/w/index.php?title=LED_lamp&oldid=512840864"