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LED lamps are significantly more energy-efficient than equivalent incandescent lamps and fluorescent lamps. LED lamps require an electronic LED circuit to operate from mains power lines, and losses from this circuit means that the efficiency of the lamp is lower than the efficiency of the LED chips it uses. The driver circuit may require special features to be compatible with lamp dimmers intended for use on incandescent lamps.
Generally the current waveform contains some amount of distortion, depending on the luminaires' technology. 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. Some LED lamps are drop-in replacements for incandescent or fluorescent lamps. LED lamps may use multiple LED packages for improved light dispersal, heat dissipation, and overall cost.
Before the introduction of LED lamps, three types of lamps were used for the bulk of general white lighting:. Considered as 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 consumed terawatthours of energy. New technological developments in light-emitting semiconductors, combined with the huge markets for displays and area lighting, encouraged the development of more energy-efficient electric lights.
The first low-powered LEDs were developed in the early s, and only produced light in the low, red frequencies of the spectrum. Borden and Gerald P. Philips Lighting ceased research on compact fluorescents in and began devoting the bulk of its research and development budget to solid-state lighting. DOE awarded Philips the prize after 18 months of extensive testing. Many other similarly efficient products followed.
Early LED lamps varied greatly in chromaticity from the incandescent lamps they were replacing.
These standards detail performance specifications for LED light sources and prescribe test methods for solid-state lighting products. Also in 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.
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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. The Illuminating Engineering Society of North America IESNA in published a documentary standard LM , which describes the methods for testing solid-state lighting products for their light output lumens , efficacy lumens per watt and chromaticity.
By electricity usage in the United States had decreased for at least five straight years, due in part to U. In Signify N. In , the first surgical goggles with LEDs were demonstrated. LED flashlights and headlamps for people were available. In , some of the first LED spotlights for use in stores were released. 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.
The firm expected the new lighting to pay for itself within 5 years. In the exceptionally large Christmas tree standing in front of the Turku Cathedral in Finland was hung with 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. By 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, [ 47 ] and many additional streetlight and municipal outdoor lighting projects soon followed. The scheme is intended to replace all the incandescent and CFL light bulbs to more efficient LED lights in the nation.
To lower the price of LED bulbs government encouraged light bulb production in the nation. A significant difference from other light sources is that the light is more directional. An LED is a " Lambertian " emitter, producing a cone of light with half-power points about 60° from the axis. A laser diode is another form of LED emitter, but produces light by a different mechanism. General-purpose lighting requires a white light, emulating a black body at a specified temperature, from "warm white" like an incandescent bulb at K, to "daylight" at around K.
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.