An LED lamp, or LED light, is a type of electric light that uses light-emitting diodes (LEDs) to produce light. LED lamps use much less energy than similar incandescent or fluorescent lamps. The most efficient LED lamps available today can produce more than 200 lumens of light for every watt of electricity used, and they turn more than half of the electricity they receive into light. LED lamps also last much longer than both incandescent and fluorescent lamps.

To work with standard household electricity, LED lamps need an electronic circuit. This circuit can reduce the overall efficiency of the lamp compared to the efficiency of the LED chips themselves. The circuit may also need special features to work with dimmer switches used for incandescent lamps. The electrical current used by LED lamps can sometimes create a distorted waveform, depending on the lamp’s design.

The market for LED lamps is expected to grow from US$75.8 billion in 2020 to US$160 billion in 2026. LED lamps reach full brightness instantly without needing time to warm up. Turning them on and off frequently does not shorten their lifespan, unlike fluorescent lamps. Over time, the brightness of LED lamps decreases slowly.

Some LED lamps can be used directly in place of incandescent or fluorescent lamps. To improve light spread, heat management, and cost, some LED lamps use multiple LED packages. Information on LED lamp packaging often includes details like light output in lumens, energy use in watts, color temperature in kelvins or as a description (such as "warm white" or "daylight"), the temperature range for safe operation, whether the lamp works with dimmer switches, if it is suitable for damp or wet environments, and sometimes the equivalent wattage of an incandescent lamp that would produce the same amount of light.

History

Before LED lamps became widely used, three main types of lamps were commonly used for general lighting:

• Incandescent lamps produce light by heating a thin wire (filament) until it glows. These lamps are not very efficient, converting only about 10–17 lumens of light per watt of electricity used. They also have a short lifespan, usually lasting around 1,000 hours. Because of their inefficiency, they are no longer used for most general lighting. Incandescent lamps emit light similar to sunlight, which helps them show colors accurately, resulting in a high Color Rendering Index (CRI).
• Fluorescent lamps create light by passing an electric current through a gas (mercury vapor) inside a glass tube. This process produces ultraviolet light, which is then converted to visible light by a special coating (phosphor) on the inside of the tube. These lamps are more efficient than incandescent lamps, producing 50–100 lumens per watt. They also last longer, up to 6,000–15,000 hours, and are used in homes and offices. However, they contain mercury, which makes them hazardous waste and requires special disposal.
• Metal-halide lamps generate light through an electric arc in a gas mixture that includes mercury, argon, and other metals, along with iodine or bromine. These lamps were among the most efficient white light sources before LEDs, producing 75–100 lumens per watt and lasting 6,000–15,000 hours. However, they need time to warm up before reaching full brightness, so they are not used in homes but in commercial, industrial, and outdoor lighting, such as streetlights. Like fluorescent lamps, they also contain mercury.

All these lamps are inefficient, converting most of their energy into heat instead of light. In 1997, global lighting used 2,016 terawatthours of electricity, and lighting consumes about 12% of the electricity used in industrialized countries. Advances in semiconductor technology, combined with demand for displays and lighting, led to the creation of more efficient light sources.

The first low-power LEDs were developed in the early 1960s, but they only produced red light. In 1968, the first commercial LEDs were introduced by Hewlett-Packard and Monsanto. However, early LEDs were not efficient enough for general lighting and were limited to use in displays and indicators.

In 1994, Shuji Nakamura of Nichia Corporation created the first high-brightness blue LED. Nakamura, along with Isamu Akasaki and Hiroshi Amano, was awarded the 2014 Nobel Prize in Physics for this invention. Blue LEDs enabled the creation of white LEDs by using a phosphor coating to convert some blue light into other colors. White LEDs became available in the early 2000s in the U.S. (Cree) and Japan (Nichia, Panasonic, Toshiba), and later in Korea and China (Samsung, Kingsun, others). In 2007, the U.S. Energy Independence and Security Act encouraged the development of energy-efficient lighting by launching the "L Prize" competition, which aimed to replace 60 W incandescent bulbs with lamps using only 17% of the energy.

In 2008, Philips Lighting stopped researching compact fluorescent lamps and focused on solid-state lighting. Philips submitted the first LED lamps to replace standard 60 W bulbs in 2009, and the U.S. Department of Energy awarded them the prize after testing. Other efficient LED products soon followed.

Early LED lamps had different colors than the incandescent lamps they replaced. To address this, the ANSI C78.377-2008 standard was created to define acceptable color ranges for LED lighting. In 2008, the National Institute of Standards and Technology (NIST) introduced the first U.S. standards for LED performance and testing.

In 2008, the Energy Star program in the U.S. and Canada began labeling LED lamps that met specific standards for starting time, lifespan, color, and performance. This program aimed to help consumers choose reliable products. A similar program in the U.K. (Energy Saving Trust) also promoted energy-efficient lighting.

In 2008, Ushio released the first LED filament lamp, and Philips introduced its first LED lamp in 2009. By 2010, Philips launched a 60 W equivalent LED lamp, and a 75 W equivalent version in 2011. The Illuminating Engineering Society of North America (IESNA) published the LM-79 standard in 2008 to guide testing of LED light output, efficiency, and color.

By 2016, experts predicted that most future lighting would be LED due to new U.S. energy standards. By 2019, U.S. electricity use had decreased for five years in a row, partly because of the switch from incandescent to LED bulbs. In 2023, Signify N.V. introduced LED lamps with EU efficiency class A, requiring at least 210 lumens per watt.

LEDs were used in various applications over the years. In 2003, the first surgical goggles with LEDs were demonstrated. Audi introduced LED headlights in its 2004 A8 W12 model. In 2005, an LED lamp was used to illuminate the Mona Lisa. By 2006, LED spotlights for stores were available, and Toyota’s Lexus LS 600h L became the first production car with LED headlights. In 2007, Audi offered headlights that used only LEDs, and Toshiba released the first commercial white LED lamp for homes.

In 2008, Sentry Equipment Corporation in the U.S. used LEDs to light its factory, with initial costs three times higher than traditional lighting. However, electricity savings recovered the extra cost within two years, and the LEDs were expected to last 20 years without replacement. In 2009, iGate, an Indian IT company, spent ₹3,700,000 (equivalent to U.S. dollars) to install LED lighting in its office, reducing energy use.

Technology

LED lamps are often made using groups of surface mount LED modules.

A major difference from other light sources is that LED light is more focused. An LED is a "Lambertian" emitter, which means it creates a cone-shaped light pattern with the brightest point in the center and the light intensity dropping off at about 60° from the center. Both laser diodes and LEDs are semiconductor light sources, but laser diodes use a process called stimulated emission, while LEDs use spontaneous emission.

General-purpose lighting needs white light that mimics the light of a black body at a certain temperature. This can range from "warm white" (like an incandescent bulb) at 2700K to "daylight" at about 6500K. Early LEDs produced light in a very narrow range of colors, determined by the energy band gap of the semiconductor material used. White light LEDs are made in two main ways: by combining light from multiple LEDs of different colors, or by using a phosphor to change some of the light into other colors. This light is not the same as true black body light, so it changes how colors look compared to an incandescent bulb. The quality of color rendering is measured by the color rendering index (CRI). As of 2019, many LED bulbs had a CRI of about 80, while more expensive high-CRI LED lighting had a CRI over 95 (100 is the ideal value).

RGB or trichromatic white LEDs use multiple LED chips that emit red, green, and blue light. These colors combine to create white light. However, the CRI is low, usually between 25 and 65, because the light is made up of a narrow range of wavelengths. Higher CRI values can be achieved by using more than three colors to cover a wider range of wavelengths.

The second method, used in most commercial LED lamps, combines an LED with a phosphor to create complementary colors from a single LED. Some of the light from the LED is absorbed by the phosphor, causing it to glow and emit light of a different color. The most common method uses a blue LED with a yellow phosphor, producing blue light and a broad range of yellow light that covers the spectrum from green to red. The CRI can range from less than 70 to over 90, though many commercial LEDs have a CRI around 82. By 2021, the efficiency of these LEDs had reached 210 lm/W, surpassing the performance of trichromatic LEDs. The phosphors used in white light LEDs can produce correlated color temperatures from 2,200 K (like a dimmed incandescent bulb) up to 7,000 K or more.

Tunable lighting systems use groups of colored LEDs that can be controlled individually, either through separate groups of each color or through multi-chip LEDs with colors combined and controlled at the chip level.

Most conventional LED lamps keep the correlated color temperature (CCT) the same when dimmed, reducing brightness without changing the light's color much. This is different from incandescent bulbs, where dimming lowers the filament temperature, causing the CCT to shift toward warmer tones (e.g., from 3000K to 1700K).

This difference happens because LEDs rely on a fixed phosphor conversion of blue light, which does not mimic the temperature-related changes in light seen in incandescent bulbs.

To fix this, specialized LED lamps called "dim-to-warm" or "warm dim" use arrays of LEDs with different CCTs or multiple phosphor layers. For example, white LEDs of different color temperatures can be combined to create an LED bulb that becomes warmer as it is dimmed. This mimics the dimming behavior of incandescent bulbs by reducing the contribution of higher CCT light as brightness decreases.

An example is Philips' "Warm Glow" technology, which shifts the color temperature downward as the bulb dims, similar to traditional incandescent bulbs.

LED chips need controlled direct current (DC) power and a circuit called an LED driver to convert alternating current (AC) from the power supply to the regulated DC used by the LEDs.

LED drivers are essential for the long life and performance of LED lamps. They can provide features like dimming and remote control. LED drivers may be built into the lamp or placed separately from the LEDs. They may also include components to meet regulations for acceptable AC line harmonic current.

LED lamps run cooler than older light sources because they do not use an electric arc or tungsten filament. However, they can still cause burns. Managing heat in high-power LEDs is important to keep the LED's junction temperature close to the surrounding air. High temperatures reduce light output and can cause failure. LEDs produce less heat for the same light output, but the heat is concentrated in a small semiconductor chip. Because of their low operating temperature, LED lamps cannot lose much heat through radiation. Instead, heat is conducted from the chip to a heat sink or cooling fin, where it is released through convection. Very high-power industrial LED lamps often use cooling fans. Some manufacturers place LEDs and circuitry in a glass bulb filled with helium gas to help cool the LEDs. Others mount LEDs on a circuit board with an aluminum backing, which is connected to the lamp's aluminum base using thermal paste. The base is then embedded in a melamine plastic shell. Because LED lamps rely on convection cooling, care must be taken when placing them in enclosed or poorly ventilated fixtures or near thermal insulation.

The term "efficiency droop" describes the decrease in light output efficiency of LEDs as the electric current increases. Instead of increasing current, light output is usually boosted by connecting multiple LED emitters in parallel and/or series in one lamp. Solving efficiency droop would allow household LED lamps to use fewer LEDs, significantly reducing costs.

Early theories suggested that efficiency droop was caused by high temperatures. However, scientists later showed that temperature was not the main cause. In 2007, the mechanism behind efficiency droop was identified as Auger recombination, a finding that received mixed reactions. A 2013 study confirmed Auger recombination as the cause.

Some lasers have been adapted as alternatives to LEDs to provide highly focused illumination.

Applications

LED lamps are used for general lighting and special purposes. When colored light is needed, LEDs that naturally produce one color of light don’t need filters that absorb energy. LED lamps are often sold as replacements for traditional bulbs or fixtures. They can replace entire fixtures, such as LED panels replacing fluorescent troffers or LED spotlights replacing halogen fixtures. They can also replace individual bulbs, like LED tubes replacing fluorescent tubes or LED HID lamps replacing HID bulbs. Replacing a fixture, like a troffer, with an LED panel means the whole panel must be replaced if it breaks, since parts like the driver cannot be easily fixed. However, replacing a bulb with an LED lamp allows the lamp to be changed separately if it fails. Some LED lamps require changes to the fixture, such as removing the ballast, while others work without any changes.

White-light LED lamps last longer and use less energy than most other lighting when used at the correct temperature. They are small, making it easier to design lighting fixtures and control how light spreads. Because LEDs are tiny, their light can be directed precisely using reflectors or lenses. LEDs using color mixing can create many colors by combining different primary colors. This allows full color mixing in lamps. Unlike other lights, LEDs emit light in a specific direction, which can be helpful or not, depending on the need. For lights that spread in all directions, a diffuser or multiple LEDs can be used.

LED lamps are made with standard shapes and connections, like an Edison screw base or GU10 fitting, and work with the electricity supplied to the socket. They include circuitry to change alternating current (AC) power into the correct voltage, usually using a switched-mode power supply.

By 2010, some LED lamps used less power than traditional bulbs. For example, a 16-watt LED lamp was as bright as a 150-watt halogen lamp. A standard incandescent bulb produces about 14 to 17 lumens per watt, depending on its size and voltage. Energy-efficient lamps that claim to be as bright as a 60-watt bulb must produce at least 806 lumens.

Some LED lamps work with dimmers. They often emit light in a specific direction. As of 2022, the best LED lamps are more energy-efficient than compact fluorescent lamps and can last 30,000 hours or more, though their lifespan decreases at higher temperatures. Incandescent bulbs last about 1,000 hours, and compact fluorescents last around 8,000 hours. Both LED and fluorescent lamps use phosphors, which lose brightness over time. Energy Star standards require LED lamps to lose less than 10% brightness after 6,000 hours of use, and no more than 15% in the worst cases. LED lamps come in many colors. Their initial cost is higher than other lamps but often results in lower total costs over time due to energy savings.

Many companies sell LED lamps for general use. The technology is improving quickly, and new energy-efficient models are available.

By 2016, LED lamps were becoming the main light source in the United States because of lower prices and the phase-out of incandescent bulbs. The Energy Independence and Security Act of 2007 banned most incandescent bulbs. LED prices have dropped, and some are sold at reduced prices by local utilities. However, in 2019, the Trump administration relaxed rules for energy-efficient bulbs. The Biden administration introduced regulations in 2023 requiring lighting to produce 45 lumens per watt, saving consumers $3 billion annually in electricity costs.

LED tube lights fit into fixtures designed for fluorescent tubes. Some can replace existing fixtures without changing the ballast, while others require removing the ballast. LED tubes use many small LEDs that emit light in one direction, unlike fluorescent tubes that spread light around the tube. Most LED tubes fit T5, T8, T10, or T12 sizes, with T8 being 26mm wide.

New lighting systems with built-in LEDs or designed for LED lamps are becoming common as older fixtures become less important. These systems do not require each bulb to have its own circuitry.

Studies showed that vegetables and ornamental plants grow well under LED lights. Trials tested plants like mint, basil, lettuce, and carrots, checking their health and growth. Ornamental plants such as primula and marigold also flowered well under LEDs.

LEDs provide efficient lighting in specific wavelengths, like red and blue, which help plants grow quickly and produce high-quality crops. Since LEDs are cool, plants can be placed close to them without overheating.

White LED lamps are now widely used where efficiency is important, such as flashlights, solar garden lights, and bicycle lights. Colored LEDs are used in traffic signals and holiday lights. LED automotive lights are popular because of their long life and small size.

By 2010, LED technology became the main choice for outdoor lighting, as early LEDs were not bright enough. A 2014 study found that color temperature and accuracy are important for LED lighting.

Comparison with other lighting technologies

Refer to the luminous efficacy chart for a comparison of efficiency among different lighting technologies.

In line with the long life claimed for LED lamps, manufacturers often offer extended warranties. However, there are currently no standardized testing procedures established by the Department of Energy in the United States to verify these claims. A typical household LED lamp is said to have an "average life" of 15,000 hours (equivalent to 15 years if used 3 hours per day) and can support 50,000 switch cycles.

Incandescent and halogen lamps naturally have a power factor of 1, but compact fluorescent and LED lamps use input rectifiers, which can lower their power factors. Lower power factors may lead to additional charges for businesses using electricity. Compact fluorescent and LED lamps can be equipped with driver circuits to achieve desired power factors, or site-wide power factor correction can be implemented. In the European Union, standards require a power factor greater than 0.4 for lamps between 2 and 5 watts, greater than 0.5 for lamps between 5 and 25 watts, and above 0.9 for lamps with higher power.

Energy Star is an international standard for energy-efficient consumer products. Products with the Energy Star label typically use 20–30% less energy than required by US standards.

Energy Star LED qualifications include:

• Reduces energy costs – uses at least 75% less energy than incandescent lighting, lowering operating expenses.
• Reduces maintenance costs – lasts 35 to 50 times longer than incandescent lighting and 2 to 5 times longer than fluorescent lighting. No lamp replacements, no ladders, and no ongoing disposal programs are needed.
• Reduces cooling costs – produces very little heat.
• Is guaranteed – comes with a minimum three-year warranty, which is longer than the industry standard.
• Offers convenient features – some indoor models include dimming, and some outdoor models have automatic daylight shut-off and motion sensors.
• Is durable – will not break like a glass bulb.

To qualify for Energy Star certification, LED lighting products must pass tests to ensure they meet the following criteria:

• Brightness is equal to or greater than existing lighting technologies (incandescent or fluorescent), with light evenly distributed across the area illuminated by the fixture.
• Light output remains constant over time, decreasing only toward the end of the rated lifetime (at least 35,000 hours or 12 years 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.
• Lights turn on instantly when activated.
• No flicker occurs when dimmed.
• No power is used in the off state, except for external controls, which should not exceed 0.5 watts in the off state.
• A power factor of at least 0.7 is required for all lamps of 5 watts or greater.

Limitations

LED lights are naturally good for dimming because they can work with many different amounts of electricity without changing color much. However, the circuits inside LED lights must be specifically made to work with certain types of dimmer switches. If they are not, the light or the dimmer switch could be damaged.

LED lights do not show colors in the same way as incandescent lights, which produce light similar to the sun. A number called CRI measures how well a light shows eight color samples. It ranges from 0 to 100. LED lights with a CRI below 75 are not good for indoor use. Poorly designed LED lights may flicker, which can be seen in slow-motion videos. The amount of flicker depends on the quality of the power supply inside the light, usually found in the base. Prolonged exposure to flickering light can cause headaches and eye strain.

The lifespan of LED lights decreases when they get too hot. Managing heat is very important when designing high-power LED lights. Like most electronic devices, LED lights are sensitive to too much heat. Also, harmful chemicals in the air can reduce their performance and shorten their life.

LED lights are expected to last about 50 times longer than common incandescent lights and much longer than fluorescent lights. This is good for users but may affect manufacturers because it reduces the need for replacements in the future.

Light can affect the body’s natural sleep cycle. Daylight has a color temperature of about 5,700K (bluish white), while tungsten lights are about 2,700K (yellow). People with sleep disorders sometimes use light therapy (exposure to bright bluish white light during the day) and dark therapy (wearing amber-tinted goggles at night to block blue light).

Some groups advise against using bluish-white lights at night. The American Medical Association does not support using bluish-white LED lights for street lighting. Studies show that switching to LED street lights may attract 48% more flying insects than older types of lights. This could harm ecosystems and increase problems like more gypsy moths near ports.