LED Basics

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Unlike incandescent lamps, LEDs are not inherently white light sources. Instead, LEDs emit nearly monochromatic light, making them highly efficient for colored light applications such as traffic lights and exit signs. However, to be used as a general light source, white light is needed. White light can be achieved with LEDs in three ways:

  • Phosphor conversion, in which a phosphor is used on or near the LED to convert the colored light to white light
  • RGB systems, in which light from multiple monochromatic LEDs (e.g., red, green, and blue) is mixed, resulting in white light
  • A hybrid method, which uses both phosphor-converted (PC) and monochromatic LEDs.

The potential of LED technology to produce high-quality white light with unprecedented energy efficiency is the primary motivation for the intense level of research and development currently supported by the U.S. Department of Energy.

Future of LEDs

There are many white LED products available on the market, and the number continues to grow, with new generations of devices constantly emerging. While many of these products perform quite well, their quality and energy efficiency can vary widely. There are standards, test procedures, and resources such as LED Lighting Facts®, ENERGY STAR®, and the DesignLights Consortium Qualified Products List that can enable buyers to make informed decisions when evaluating LED lighting.

LED lighting technology has improved dramatically over the past 10 years. Improvements in technology have enabled LEDs to achieve the highest lighting efficacies. And LED lighting costs have come down considerably, resulting in significant adoption. Despite this progress, further improvements are both possible and desirable. The technology can be improved in efficiency and in other features, such as color quality, light distribution, form factor, and building integration. The manufacturing technology for LED lighting can also be improved to reduce cost and increase market penetration, resulting in the greatest possible energy savings for the nation.

Frequently Asked Questions

How is LED lighting different from other energy-efficient lighting technologies?

LEDs offer the potential for cutting general lighting energy use nearly in half by 2030, saving energy dollars and carbon emissions in the process. Their unique characteristics—including compact size, long life, resistance to breakage and vibration, good performance in cold temperatures, lack of infrared or ultraviolet emissions, and instant-on performance—are beneficial in many lighting applications. The ability to be dimmed and to provide color control are other benefits of the LED lighting technology platform.

One of the defining features of LEDs is that they emit light in a specific direction, which reduces the need for reflectors and diffusers that can lower efficiency. In contrast, fluorescent and "bulb"-shaped incandescent lamps emit light in all directions, with the result that much of the light they produce is lost within the fixture, escapes in a direction not useful for the intended application, or requires pricey and bulky optics to get the light in the right place. With many fixture types, including recessed downlights, troffers, and undercabinet fixtures, it is not uncommon for only 50 to 60% of the total light produced to be emitted.  

In addition, LED sources are inherently dimmable and instantaneously controllable, and they can be readily integrated with sensor and control systems, thus enabling further energy savings through the use of occupancy sensing, daylight harvesting, and local control of light levels. LED technology also offers the prospect of full color control over the light spectrum. What this all adds up to is the potential to improve the performance and value of lighting in totally new ways. 

How energy efficient are LEDs?

LED lighting has the potential to be more energy efficient than any other known lighting technology. But, two aspects of energy efficiency are important to consider: the efficiency of the LED device itself (source efficacy) and how well the device and fixture work together in providing the necessary lighting (luminaire efficacy). How much electricity is consumed depends not only on the LED device, but also on the lighting fixture design. Because they are sensitive to thermal and electrical conditions, LEDs must be carefully integrated into lighting fixtures. The efficiency of a poorly designed fixture that uses even the best LEDs will be only a fraction of what it would be if the fixture were well-designed, and the design can also affect lumen maintenance.

Energy performance of white LED products continues to improve rapidly. DOE's long-term R&D goal calls for cost-effective, warm-white LED packages producing 250-350 lumens per watt. This chart shows typical luminous efficacies for traditional and LED sources, including ballast losses as applicable.

PRODUCT TYPELUMINOUS EFFICACY (IN LM/W)
LED A19 lamp (dimmable, warm white)79
LED PAR38 lamp (warm white)68
LED T8 tube (neutral white)109
LED 6" downlight (warm white)58
LED troffer 2'x4' (warm white)100
LED high/low-bay fixture (warm white)113
LED street light103
OLED luminaire43
High intensity discharge system (high watt)115
Linear fluorescent system108
High intensity discharge system (low watt)104
Compact fluorescent lamp A19 replacement70
Compact fluorescent lamp A19 replacement (dimmable)70
Halogen A1920
Incandescent A1915

Source: 2017 Solid-State Lighting R&D Plan

Do LEDs provide high-quality light?
Key aspects of high-quality light are the color appearance of the light itself, which is described by its color coordinates but is often condensed (with significant loss of information) to correlated color temperature (CCT), and how the light affects the color appearance of objects, which is referred to as color fidelity. Color fidelity can be quantified using the color rendering index (CRI), or with one of several other recently developed metrics. LED light sources have demonstrated that they can achieve a wide range of color qualities, depending on the demands of the lighting application. However, to achieve high levels of color quality, there are typically cost and efficiency tradeoffs. In general, a minimum CRI of 80 is recommended for interior lighting, and LED products can readily achieve this performance. CRI of 90 or higher indicates excellent color fidelity; LEDs can also meet this threshold. CRI is far from a perfect metric and is especially poor at predicting the fidelity of saturated reds, for which the supplemental value R9 is often used. New metrics, such as the fidelity index (Rf) and the gamut index (Rg­), which are described in IES TM-30-15, can provide a more comprehensive evaluation of color rendering. Learn more about TM-30-15 and LED color characteristics
How long do LEDs last?

LED luminaire useful life is often described by the number of operating hours until the LED luminaire is emitting 70 percent of its initial light output. Good-quality white LED lighting products are expected to have a useful life of 30,000 to 50,000 hours or even longer. A typical incandescent lamp lasts about 1,000 hours; a comparable CFL, 8,000 to 10,000 hours; and the best linear fluorescent lamps, more than 30,000 hours. Learn more about LED lifetime and reliability

Other aspects of reliability should also be considered. Catastrophic failure describes the situation where a luminaire no longer emits light, typically due to an electronics failure. The long life of the LED means that there is ample opportunity for the electronics to fail before the LEDs go bad. Another type of failure is due to color shift. All light sources change color over time. The long expected life of an LED lighting product means that before the LED fails, the color of the light may shift to an unacceptable degree, depending on the application. In general, LED lighting lives up to its promise for long life, but all aspects of reliability should be considered when selecting a product.

Are LEDs cost-effective?

Costs of LED lighting products vary widely. Some LED bulbs can cost as little as $1 – $2, but other LED lighting products may carry a significant cost premium compared to standard lighting technologies. In general, LED lighting products are still more expensive than their conventional counterparts, but when the costs of energy and maintenance are included in the total cost of ownership, LED-based products can have a distinct advantage. And differences among LED lighting products typically correspond with differences in various lighting performance features, such as color quality, lifetime, optical performance, and dimmability.  Learn more about cost-effectiveness trends in the latest SSL R&D Plan

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