1. History
    Examples of early adoption 

2. Technology overview
    White light LEDs  Color changing LED lighting  LED drivers  Thermal management  Efficiency droop 

3. Application
    Household LED lamp  Lamp sizes and bases  LED tube lamps  Lighting designed for LEDs  Plant  Specialty  Outdoor LED lighting 

4. Comparison of common SMD (surface mounted) LED modules

5. Comparison to other lighting technologies
    Comparison table  Energy Star qualification 

6. Limitations

7. See also

8. References

9. Further reading

10. External links

An LED lamp or LED light bulb is an electric light for use in light fixtures that produces light using one or more light-emitting diodes (LEDs). LED lamps have a lifespan many times longer than equivalent incandescent lamps, and are significantly more efficient than most fluorescent lamps,^[1][2][3] with some LED chips able to emit up to 303 lumens per watt (as claimed by Cree and some other LED manufacturers).^[4] However, LED lamps require an electronic LED driver circuit when operated from mains power lines, and losses from this circuit mean the efficiency of the lamp is lower than the efficiency of the LED chips it uses. The most efficient commercially available LED lamps have efficiencies of 200 lumens per watt (Lm/W).^[5][6][7] Commercially available LED chips have efficiencies of over 220 Lm/W.{{cn|date=August 2018}} The LED lamp market is projected to grow by more than twelve-fold over the next decade, from $2 billion in the beginning of 2014 to $25 billion in 2023, a compound annual growth rate (CAGR) of 25%.^[8] {{as of|2016}}, LEDs use only about 10% of the energy an incandescent lamp requires.^[9]

Similar to incandescent lamps (and unlike most fluorescent lamps), LEDs come to full brightness immediately with no warm-up delay. Frequent switching on and off does not reduce life expectancy as with fluorescent lighting.^[10] Light output decreases gradually over the lifetime of the LED (see Efficiency droop section).

Some LED lamps are made to be a directly compatible drop-in replacement for incandescent or fluorescent lamps. LED lamp packaging may show the light outpur in lumens, the power consumption in watts, the color temperature in Kelvin or a colour description such as "warm white", "cool white" or "daylight", the operating temperature range, and sometimes the equivalent wattage of an incandescent lamp delivering the same output in lumens.

The directional emission characteristics of LEDs affect the design of lamps. While a single power LED may produce as much light output as an incandescent lamp using several times as much power, in most general lighting applications multiple LEDs are used. This can form a lamp with improved cost, light distribution, heat dissipation and possibly also color-rendering characteristics.

LEDs run on direct current (DC), whereas mains current is alternating current (AC) and usually at much higher voltage than the LED can accept. LED lamps can contain a circuit for converting the mains AC into DC at the correct voltage. These circuits contain rectifiers, capacitors, and may have other active electronic components, which may also permit the lamp to be dimmed. In an LED filament lamp, the driving circuit is simplified because many LED junctions in series have approximately the same operating voltage as the AC supply.

History

Before the introduction of LED lamps, three types of lamps were used for the bulk of general (white) lighting:

• Incandescent lights, which produce light with a glowing filament heated by electric current. These are very inefficient, having a luminous efficacy of 10-17 lumens/W, and also have a short lifetime of 1000 hours. They are being phased out of general lighting applications. Incandescent lamps produce a continuous black body spectrum of light similar to sunlight, and so produce high Color rendering index (CRI).
• Fluorescent lamps, which produce ultraviolet light by a glow discharge between two electrodes in a low pressure tube of mercury vapor, which is converted to visible light by a fluorescent coating on the inside of the tube. These are more efficient than incandescent lights, having a luminous efficacy of around 60 lumens/W, and have a longer lifetime 6,000-15,000 hours, and are widely used for residential and office lighting. However, their mercury content makes them a hazard to the environment, and they have to be disposed of as hazardous waste.
• Metal-halide lamps, which produce light by an arc between two electrodes in an atmosphere of argon, mercury and other metals, and iodine or bromine. These were the most efficient white electric lights before LEDs, having a luminous efficacy of 75–100 lumens/W and have a relatively long bulb lifetime of 6,000-15,000 hours, but because they require a 5 - 7 minute warmup period before turning on, are not used for residential lighting, but for commercial and industrial wide area lighting, and outdoor security lights and streetlights. Like fluorescents, they also contain hazardous mercury.

Considered as electric energy converters, all these existing lamps are inefficient, emitting more of their input energy as waste heat than as visible light. Global electric lighting in 1997 consumed 2016 terawatthours of energy. Lighting consumes roughly 12% of electrical energy produced by industrialized countries. The increasing scarcity of energy resources, and the environmental costs of producing energy, particularly the discovery of global warming due to carbon dioxide emitted by the burning of fossil fuels, which are the largest source of energy for electric power generation, created an increased incentive to develop more energy-efficient electric lights.

The first low-powered LEDs were developed in the early 1960s, and only produced light in the low, red frequencies of the spectrum. The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994.^[11] The existence of blue LEDs and high-efficiency LEDs led to the development of the first 'white LED', which employed a phosphor coating to partially convert the emitted blue light to red and green frequencies creating a light that appears white.^[12] Isamu Akasaki, Hiroshi Amano and Nakamura were later awarded the 2014 Nobel Prize in Physics for the invention of the blue LED.^[13]

China further boosted LED research and development in 1995 and demonstrated its first LED Christmas tree in 1998. The new LED technology application then became prevalent at the start of the 21st century by US (Cree) and Japan (Nichia, Panasonic, Toshiba, etc.) and then starting 2004 by Korea and China (Samsung, Kingsun, Solstice, Hoyol, etc.)^[14][15]

In the USA, the Energy Independence and Security Act (EISA) of 2007 authorized the Department of Energy (DOE) to establish the Bright Tomorrow Lighting Prize competition, known as the "L Prize",^[16] the first government-sponsored technology competition designed to challenge industry to develop replacements for 60 W incandescent lamps and PAR 38 halogen lamps. The EISA legislation established basic requirements and prize amounts for each of the two competition categories, and authorized up to $20 million in cash prizes.^[17] The competition also included the possibility for winners to obtain federal purchasing agreements, utility programs, and other incentives. In May 2008, they announced details of the competition and technical requirements for each category. Lighting products meeting the competition requirements could use just 17% of the energy used by most incandescent lamps in use today. That same year the DOE also launched the Energy Star program for solid-state lighting products. The EISA legislation also authorized an additional L Prize program for developing a new "21st Century Lamp".

Philips Lighting ceased research on compact fluorescents in 2008 and began devoting the bulk of its research and development budget to solid-state lighting.^[18] On 24 September 2009, Philips Lighting North America became the first to submit lamps in the category to replace the standard 60 W A-19 "Edison screw fixture" light bulb,^[19] with a design based on their earlier "AmbientLED" consumer product. On 3 August 2011, DOE awarded the prize in the 60 W replacement category to a Philips LED lamp after 18 months of extensive testing.^[18]

Early LED lamps varied greatly in chromaticity from the incandescent lamps they were replacing. A standard was developed, ANSI C78.377-2008, that specified the recommended color ranges for solid-state lighting products using cool to warm white LEDs with various correlated color temperatures.^[19] In June 2008, NIST announced the first two standards for solid-state lighting in the United States. These standards detail performance specifications for LED light sources and prescribe test methods for solid-state lighting products.

Also in 2008 in the United States and Canada, the Energy Star program began to label 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.^[20] [https://www.energystar.gov/products/lighting_fans/light_bulbs Energy Star Certified Light Bulbs] is a resource for finding and comparing Energy Star qualified lamps. A similar program in the United Kingdom (run by the Energy Saving Trust) was launched to identify lighting products that meet energy conservation and performance guidelines.^[21]

The Illuminating Engineering Society of North America (IESNA) in 2008 published a documentary standard LM-79, which describes the methods for testing solid-state lighting products for their light output (lumens), efficacy (lumens per watt) and chromaticity.

In January 2009, it was reported that researchers at University of Cambridge had developed an LED lamp that costs £2 (about $3 U.S.), is 12 times as energy efficient as a tungsten lamp, and lasts for 100,000 hours.^[22]

Examples of early adoption

In 2008 Sentry Equipment Corporation in Oconomowoc, Wisconsin, US, was able to light its new factory interior and exterior almost solely with LEDs. Initial cost was three times that of a traditional mix of incandescent and fluorescent lamps, but the extra cost was recovered within two years via electricity savings, and the lamps should not need replacing for 20 years.^[24] In 2009 the Manapakkam, Chennai office of the Indian IT company, iGate, spent {{Currency|3700000|INR}} ({{Currency|80000|USD}}) to light {{convert|57000|sqft|m2|abbr=on}} of office space with LEDs. The firm expected the new lighting to pay for itself within 5 years.^[25]

In 2009 the exceptionally large Christmas tree standing in front of the Turku Cathedral in Finland was hung with 710 LED lamps, each using 2 watts. It has been calculated that these LED lamps paid for themselves in three and a half years, even though the lights run for only 48 days per year.^[26]

In 2009 a new highway (A29) was inaugurated in Aveiro, Portugal; it included the first European public LED-based lighting highway.^[27]

By 2010 mass installations of LED lighting for commercial and public uses were becoming common. LED lamps were used for a number of demonstration projects for outdoor lighting and LED street lights. The United States Department of Energy made several reports available on the results of many pilot projects for municipal outdoor lighting,^[28] and many additional streetlight and municipal outdoor lighting projects soon followed.^[29]

Technology overview

LED lamps are often made with arrays of surface mount LED modules (SMD modules) that replace incandescent or compact fluorescent lamps, mostly replacing incandescent lamps rated from 5 to 200 watts.

A significant difference from other light sources is that the light is more directional, i.e., emitted as a narrower beam.

White light LEDs

General-purpose lighting requires a basically white light, emulating a black body at a specified temperature, from "warm white" (like an incandescent bulb) at 2700K, to "daylight" at around 6000K. The first LEDs emitted light in a very narrow band of wavelengths, of a color characteristic of the energy band gap of the semiconductor material used to make the LED. LEDs that emit white light are made using two principal methods: either mixing light from multiple LEDs of various colors, or using a phosphor to convert some of the light to other colors. The light is not the same as a true black body, giving a different appearance to colors than an incandescent bulb. Color rendering quality is specified by the CRI, and {{As of|2019|lc=y}} is about 80 for many LED bulbs, and over 95 for more expensive high-CRI LED lighting (100 is the ideal value).

RGB or trichromatic white LEDs use multiple LED chips emitting red, green, and blue wavelengths. These three colors combine to produce white light. The color rendering index (CRI) is poor, typically 25 - 65, due to the narrow range of wavelengths emitted.^[30] Higher CRI values can be obtained using more than three LED colors to cover a greater range of wavelengths.

The second basic method uses LEDs in conjunction with a phosphor to produce complementary colors from a single LED. Some of the light from the LED is absorbed by the molecules of the phosphor, causing them to fluoresce, emitting light of another color via the Stokes shift. The most common method is to combine a blue LED with a yellow phosphor, producing a narrow range of blue wavelengths and a broad band of "yellow" wavelengths actually covering the spectrum from green to red. The CRI value can range from less than 70 to over 90, although a wide range of commercial LEDs of this type have a color rendering index around 82.^[30] Following successive increases in efficacy, which has reached 150 lm/W on a production basis as of 2017, this type has surpassed the performance of trichromatic LEDs.

The phosphors used in white light LEDs can give correlated color temperatures in the range of 2,200 K (dimmed incandescent) up to 7,000 K or more.^[31]

Color changing LED lighting

Tunable lighting systems employ banks of colored LEDs that can be individually controlled, either using separate banks of each color, or multi-chip LEDs with the colors combined and controlled at the chip level.^[32] For example, white LEDs of different color temperatures can be combined to construct an LED bulb that decreases its color temperature when dimmed.^[33]

LED drivers

LED chips require controlled direct current (DC) electrical power and an appropriate circuit as an LED driver is required to convert the alternating current from the power supply to the regulated voltage direct current used by the LEDs.

LED drivers are the essential components of LED lamps or luminaries. A good LED driver can guarantee a long life for an LED system and provide additional features such as dimming and control. The LED drivers can be put inside the lamp or luminaire, which is called a built-in type (or integral), or be put outside, which is called an independent type (or remote). According to different applications, different types of LED drivers need to be applied; for example, an outdoor driver for street light, an indoor point driver for a down light, and an indoor linear driver for a panel light.

Thermal management

Compared to other lighting systems LEDs must be kept cool as high temperatures can cause premature failure and reduced light output. Thermal management of high-power LEDs is required to keep the junction temperature close to ambient temperature. LED lamps typically include heat dissipation elements such as heat sinks and cooling fins and very high power lamps for industrial uses are frequently equipped with cooling fans.^[34]

Efficiency droop

The term "efficiency droop" refers to the decrease in luminous efficacy of LEDs as the electric current increases above tens of milliamps (mA). Instead of increasing current levels, luminance is usually increased by combining multiple LEDs in one lamp. Solving the problem of efficiency droop would mean that household LED lamps would require fewer LEDs, which would significantly reduce costs.

In addition to being less efficient, operating LEDs at higher electric currents produces high temperatures which compromise the lifetime of the LED. Because of this increased heating at higher currents, high-brightness LEDs have an industry standard of operating at only 350 mA, giving a good compromise between light output, efficiency, and longevity.^{[35][36][37][38]}

Early suspicions were that the LED droop was caused by elevated temperatures. Scientists proved the opposite to be true—that, although the life of the LED would be shortened, elevated temperatures actually improved the efficiency of the LED.^[39] The mechanism causing efficiency droop was identified in 2007 as Auger recombination, which was taken with mixed reaction.^[38] A 2013 study conclusively identified Auger recombination as the cause of efficiency droop.^[40]

Application

LED lamps are used for both general and special-purpose lighting. Where colored light is needed, LEDs that inherently emit light of a single color require no energy-absorbing filters.

White-light LED lamps have longer life expectancy and higher efficiency (more light for the same electricity) than most other lighting when used at the proper temperature. 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,^[42] and the light output and spatial distribution of an LED array can be controlled with no efficiency loss.

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.^[43] Unlike other lighting technologies, LED emission tends to be directional (or at least Lambertian), which can be either advantageous or disadvantageous, 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 lamp

Lamp sizes and bases

LED lamps are made with standard lamp connections and shapes, such as an Edison screw base, an MR16 shape with a bi-pin base, or a GU5.3 (bi-pin cap) or GU10 (bayonet fitting) and are made compatible with the voltage supplied to the sockets. They include driver circuitry to rectify the AC power and convert the voltage to an appropriate value, usually a switched-mode power supply.

Some models of LED lamps are compatible with dimmers as used for incandescent lamps^[50] (although dimmers for incandescent lighting are not suitable for LEDs). LED lamps often have directional light characteristics. These lamps are more power-efficient than compact fluorescent lamps^[46]{{better source|date=January 2017}} and offer lifespans of 30,000 or more hours, reduced if operated at a higher temperature than specified. Incandescent lamps have a typical life of 1,000 hours,^[47] and compact fluorescents about 8,000 hours.^[48] The lamps maintain output light intensity well over their lifetimes. Energy Star specifications require the lamps to typically drop less than 10% after 6,000 or more hours of operation, and in the worst case not more than 15%.^[49] LED lamps are available with a variety of color properties. The purchase price is higher than most other lamps—although dropping—but the higher efficiency may usually makes total cost of ownership (purchase price plus cost of electricity and changing bulbs) lower.^[50]

Several companies offer LED lamps for general lighting purposes. The technology is improving rapidly and new energy-efficient consumer LED lamps are available.^[51][52]

LED tube lamps

LED tube lights are designed to physically fit in fixtures intended for fluorescent tubes. Some LED tubular lamps are intended to be a drop-in replacement into existing fixtures if appropriate ballast is used. Others require rewiring of the fixtures to remove the ballast. An LED tube lamp generally uses many individual Surface-Mounted LEDs which are directional and require proper orientation during installation as opposed to Fluorescent tube lamps which emit light in all directions around the tube. Most LED tube lights available can be used in place of T5, T8, T10, or T12 tube designations, T8 is D26mm, T10 is D30mm, in lengths of {{convert|590|mm|abbr=on}}, {{convert|1200|mm|abbr=on}} and {{convert|1500|mm|abbr=on}}.

Lighting designed for LEDs

Newer light fittings with long-lived LEDs built-in, or designed for LED lamps, have been coming into use as the need for compatibility with existing fittings diminishes. Such lighting does not require each bulb to contain circuitry to operate from mains voltage.

Plant

Experiments revealed surprising performance and production of vegetables and ornamental plants under LED light sources.^[55] Many plant species have been assessed in greenhouse trials to make sure that the quality of biomass and biochemical ingredients of such plants is at least comparable with those grown in field conditions. Plant performance of mint, basil, lentil, lettuce, cabbage, parsley and carrot was measured by assessing both the health and vigor of the plants and the success of the LEDs in promoting growth. Also noticed was profuse flowering of select ornamentals including primula, marigold and stock.^[55][56]

Light emitting diodes (LEDs) offer efficient electric lighting in desired wavelengths (red + blue) which support greenhouse production in minimum time and with high quality and quantity. As LEDs are cool, plants can be placed very close to light sources without overheating or scorching, requiring much less space for intense cultivation than with hot-running lighting.

Specialty

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. Colored LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright light of the required color is essential, and in strings of holiday lights. LED automotive lamps are widely used for their long life and small size. Multiple LEDs are used in applications where more light output than available from a single LED is required.

Outdoor LED lighting

By about 2010 LED technology came to dominate the outdoor lighting industry; earlier LEDs were not bright enough for outdoor lighting. A study completed in 2014 concluded that color temperature and accuracy of LED lights was easily recognized by consumers, with preference towards LEDs at natural color temperatures.^[57] LEDs are now able to match the brightness and warmer color temperature that consumers desire from their outdoor lighting system.

LEDs are increasingly used for street lighting in place of mercury and sodium lamps due to their lower running and lamp replacement costs. However, there have been concerns that the use of LED street lighting with predominantly blue light can cause eye damage, and that some LEDs switch on and off at twice mains frequency, causing malaise in some people, and possibly being misleading with rotating machinery due to stroboscopic effects. These concerns can be addressed by use of appropriate lighting, rather than simple concern with cost.^[58]

Comparison of common SMD (surface mounted) LED modules

The light from white LED lamps is usually provided by industry standard LED surface-mounted devices (SMD's).^[59] Non-SMD types of LED lighting also exist, such COB (chip on board) and MCOB (multi-COB).

SMD LED Modules are described by the dimensions of the LED package. A single multicolor module may have 3 individual LEDs within that package, one each of red, green and blue, to allow many colors or shades of white to be selected, by varying the brightness of the individual LEDs. LED brightness may be increased by using a higher driving current, at the cost of reducing the device's lifespan.

Comparison to other lighting 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 over a broad range of wavelengths. Incandescent sources yield a "warm" yellow or white color quality depending on the filament operating temperature. Incandescent lamps emit 98% of the energy input as heat.^[62] A 100 W light bulb for 120 V operation emits about 1,700 lumens, about 17 lumens/W;^[63] for 230 V bulbs the figures are 1340 lm and 13.4 lm/W.^[64] Incandescent lamps are relatively inexpensive to make. The typical lifespan of an AC incandescent lamp is 750 to 1,000 hours.^[65][66] They work well with dimmers. Most older light fixtures are designed for the size and shape of these traditional bulbs. In the U.S. the regular sockets are E26 and E11, and E27 and E14 in some European countries.

• Halogen lamps (also known as "quartz-halogen") are just incandescent lamps that run at a higher temperature than standard incandescents. They are slightly more efficient.

• Fluorescent lamps 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. Conventional linear fluorescent lamps have life spans around 20,000 and 30,000 hours based on 3 hours per cycle according to lamps NLPIP reviewed in 2006. Induction fluorescent relies on electromagnetism rather than the cathodes used to start conventional linear fluorescent. The newer rare earth triphosphor blend linear fluorescent lamps made by Osram, Philips, Crompton and others have a life expectancy greater than 40,000 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 ballast-lamp combined system efficacy for then current linear fluorescent systems in 1998 as tested by NLPIP ranged from 80 to 90 lm/W.^[67]
• Compact fluorescent lamps' specified lifespan typically ranges from 6,000 hours to 15,000 hours.^[65]
• Electricity prices vary in different areas of the world, and are customer dependent. In the US generally, commercial (0.103 USD/kWh) and industrial (0.068 USD/kWh) electricity prices are lower than residential (0.123 USD/kWh) due to fewer transmission losses.^[68]
• High-pressure sodium lamps give around 100 lumens/watt which is very similar to LED lamps. They have much shorter life than LEDs, and their color rendering index is low. They are commonly used for outdoor lighting and in grow lamps.

Comparison table

In keeping with the long life claimed for LED lamps, long warranties are offered. However, currently there are no standardized testing procedures set by the Department of Energy in the United States to prove these assertions by each manufacturer.^[77] A typical domestic LED lamp is stated to have an "average life" of 15,000 hours (15 years at 3 hours/day), and to support 50,000 switch cycles.^[78]

Incandescent and halogen lamps naturally have a power factor of 1, but Compact fluorescent and LED lamps use input rectifiers and this causes lower power factors. Low power factors can result in surcharges for commercial energy users; CFL and LED lamps are available with driver circuits to provide any desired power factor, or site-wide power factor correction can be performed. EU standards requires a power factor better than 0.5 for lamp powers up to 25 watts and above 0.9 for higher power lamps.^[79]

Energy Star qualification

• Reduces energy costs — uses at least 75% less energy than incandescent lighting, saving on operating expenses.
• Reduces maintenance costs — lasts 35 to 50 times longer than incandescent lighting and about 2 to 5 times longer than fluorescent lighting. No lamp-replacements, no ladders, no ongoing disposal program.
• Reduces cooling costs — LEDs produce very little heat.
• Is guaranteed — comes with a minimum three-year warranty — far beyond the industry standard.
• Offers convenient features — available with dimming on some indoor models and automatic daylight shut-off and motion sensors on some outdoor models.
• Is durable – won't break like a bulb.

To qualify for Energy Star certification, LED lighting products must pass a variety of tests to prove that the products will display the following characteristics:

• Brightness is equal to or greater than existing lighting technologies (incandescent or fluorescent) and light is well distributed over the area lit by the fixture.
• Light output remains constant over time, only decreasing towards the end of the rated lifetime (at least 35,000 hours or 12 annums based on use of 8 hours per day).
• Excellent color quality. The shade of white light appears clear and consistent over time.
• Efficiency is as good as or better than fluorescent lighting.
• Light comes on instantly when turned on.
• No flicker when dimmed.
• No off-state power draw. The fixture does not use power when it is turned off, with the exception of external controls, whose power should not exceed 0.5 watts in the off state.
• Power factor of at least 0.7 for all lamps of 5W or greater.

Limitations

Many will not work with existing dimmer switches designed for higher power incandescent lamps.^[84]

Color rendering is not identical to incandescent lamps which emit close to perfect black-body radiation as that from the sun and for what eyes have evolved. A measurement unit called CRI is used to express how the light source's ability to render the eight color sample chips compare to a reference on a scale from 0 to 100.^[85] LEDs with CRI below 75 are not recommended for use in indoor lighting.^[86]

LED lamps may flicker. The effect can be seen on a slow motion video of such a lamp. The extent of flicker is based on the quality of the DC power supply built into the lamp structure, usually located in the lamp base. Longer exposures to flickering light contribute to headaches and eye strain.^[87][88][89]

LED life span drops at higher temperatures, which limits the power that can be used in lamps that physically replace existing filament and compact fluorescent types. Thermal management of high-power LEDs is a significant factor in design of solid state lighting equipment. LED lamps are sensitive to excessive heat, like most solid state electronic components. LED lamps should be checked for compatibility for use in totally or partially enclosed fixtures before installation as heat build-up could cause lamp failure and/or fire.{{citation needed|date=March 2018}}

The long life of LEDs, expected to be about 50 times that of the most common incandescent lamps and significantly longer than fluorescent types, is advantageous for users but will affect manufacturers as it reduces the market for replacements in the distant future.^[24]

The human circadian rhythm can be affected by light sources.^[90][91] The effective color temperature of daylight is ~5,700K^[92] (bluish white) while tungsten lamps are ~2,700K (yellow).^[93] People who have circadian rhythm sleep disorders are sometimes treated with light therapy (exposure to intense bluish white light during the day) and dark therapy (wearing amber-tinted goggles at night to reduce bluish light).^[94][95][96]

Some organizations recommend that people should not use bluish white lamps at night. The American Medical Association argues against using bluish white LEDs for municipal street lighting.^[97]

Research suggests that the shift to LED street lighting attracts 48% more flying insects than HPS lamps, which could cause direct ecological impacts as well as indirect impacts such as attracting more gypsy moths to port areas.^[98]

See also

• LED display
• LED headlamp
• LED filament
• List of emerging technologies
• List of light sources
• Lux
• Photometry (optics)
• Radiation angle
• Solar lamp
• Spectroscopy

References

Further reading

• {{cite book|author=E. Fred Schubert|title=Light-Emitting Diodes|url=https://books.google.com/books?id=0H4bWIpaXb0C|date=8 June 2006|publisher=Cambridge University Press|isbn=978-1-139-45522-0}}
• {{cite journal|doi=10.1016/j.neuroscience.2016.10.015|pmid=27751961|year=2016|author1=Krigel|first1=A|title=Light-induced retinal damage using different light sources, protocols and rat strains reveals LED phototoxicity|journal=Neuroscience|volume=339|pages=296–307|last2=Berdugo|first2=M|last3=Picard|first3=E|last4=Levy-Boukris|first4=R|last5=Jaadane|first5=I|last6=Jonet|first6=L|last7=Dernigoghossian|first7=M|last8=Andrieu-Soler|first8=C|last9=Torriglia|first9=A|last10=Behar-Cohen|first10=F|url=http://hal.upmc.fr/hal-01383394/file/Krigel_Light-induced.pdf}}

External links

• [https://web.archive.org/web/20091212014857/http://www.e-lumen.eu/ e-lumen.eu] – a website from the European Commission about the second generation of energy-saving lightbulbs
• [https://www.washingtonpost.com/national/health-science/some-cities-are-taking-another-look-at-led-lighting-after-ama-warning/2016/09/21/98779568-7c3d-11e6-bd86-b7bbd53d2b5d_story.html Some cities are taking another look at LED lighting after AMA warning] (25 Sept 2016), The Washington Post

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