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An LED is a light-emitting diode. LEDs consist of a semiconductor diode that emits light when a voltage is applied to it. LED technology has been used for several decades as indicator lights for electronic devices and now is useful in lighting technology.

How are LEDs used?

LEDs are historically popular with architectural highlighting. Red, Green, and blue LEDs are commonly used for traffic lights and exit signs. Currently, the LED has evolved and can be used in indoor and outdoor lighting fixtures.

Have LEDs always been used in general illumination lighting?

LEDs have not always been used for general lighting. Experts have tested and created LEDs to ensure that lumen-per-watt ratio is at least as good as existing technology and that the color quality meets industry standards. The lighting industry can now offer products for general illumination, indoor and outdoor lighting.

How has new LED technology improved?

LED technology is rapidly evolving, showing significant promise in efficiency, color consistency, color quality, and in the ability to produce more reliable light over time. As the technology improves, the ways that LEDs can be used for general illumination is expected to expand.

What are the advantages to using LED lights?

High efficiency and durability are the most pronounced benefits of using LED lights. Longer lifespan and low maintenance helps you save energy and money as you invest in LEDs for your lighting needs.

What's the difference between efficiency and efficacy?

Efficacy applies to input and output of units. We measure the amount of light (lumens) produced by a certain amount of electricity (in watts). Efficiency refers to the ratio of the total lumens released from a fixture to the total lumens produced by a light source.

How are LED products evaluated?

Evaluating an LED product can seem complex. One must consider the overall system efficiency, optical control, thermal management, and luminosity, and at what point in time the fixture will reach 30 percent lumen depreciation.

Coal-fired power generation accounts for roughly 40 percent of the mercury emissions in the U.S.

The department of energy concluded in its solid-state lighting (SSL) commercial product testing program: "Until the field of SSL technologies and supporting knowledge matures, any claims regarding performance of SSL luminaires should be based on overall luminaire efficacy (i.e., from testing of the entire luminaire, including LEDs, drivers, heat sinks, optical lenses and housing), to avoid misleading buyers and causing long-term damage to the SSL market."

What is junction temperature?

Junction temperature is the temperature at the point where an individual diode connects to its base. Maintaining a low junction temperature increases output and slows LED lumen depreciation. Junction temperature is a key metric for evaluating an LED product's quality and ability to deliver long life.

The three things affecting junction temperature are: drive current, thermal path, and ambient temperature. In general, the higher the drive current, the greater the heat generated at the die. Heat must be moved away from the die in order to maintain expected light output, life, and color. The amount of heat that can be removed depends upon the ambient temperature and the design of the thermal path from the die to the surroundings.

The department of energy advises: "Heat management and an awareness of the operating environment are critical considerations to the design and application of LED luminaires for general illumination. Successful products will use superior heat sink designs to dissipate heat, and minimize junction temperature. Keeping the junction temperature as low as possible and within manufacturer specifications is necessary in order to maximize the performance potential of LEDs."

Why Does Thermal Management Matter?

LEDs release heat that has built up inside a fixture, using a low junction temperature and innovative engineering. The heat flows out through a heat pipe assembly which can preserve the life of your LED. Some products releases warm air while circulating cooler air through the fixture using airflow convection technology. Look for products that assist in saving heat and helping you save money.

Why is the lifespan of an LED measured as lumen depreciation?

An LEDs lifespan is measured by lumen depreciation because most LED light sources will decrease in light output over time rather than burning out like other technologies. Some LEDs can burn out but most just grow dim over time. The industry measures the decrease of light output (lumen depreciation) to inform consumers of the amount light to be emitted from an LED fixture or bulb.

The Illuminating Engineering Society's (IES) current standard recommends that lifetime of LED lights be based on the point where the product loses 30 percent of its initial light output. This is called the L70, meaning the estimated point where the LED light produces only 70 percent of its initial light output. There are other industry methods for estimating lifetime that take other things into consideration but this is the most widely accepted.

LED lifespan refers to the point at which it has reached 30 percent lumen depreciation. At 50,000 hours an LED burns on a decreased lumen output.

What is equivalent to 50,000 hours as a fixture is illuminated?

24 hours a day, 5.7 years

18 hours per day, 7.4 years

8 hours per day, 17.1 years