Applications

    

Timeline

    

  

  

    

        

  

  

Solid-state lighting (SSL) refers to a type of lighting that uses semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gas.[citation needed]

The term "solid state" refers commonly to light emitted by solid-state electroluminescence, as opposed to incandescent bulbs (which use thermal radiation) or fluorescent tubes. Compared to incandescent lighting, SSL creates visible light with reduced heat generation or parasitic energy dissipation. Even conventional fluorescent lamps are essentially solid state light sources, as most light is generated in the solid state fluorescent coating of the tube. Conventional incandescent light bulbs are essentially solid state light sources too, as light is generated in the solid state tungsten filament. The distinction is even more blurry in the case of most common "white" LEDs which convert blue light to an (approximate) white light spectrum using photoluminescence, the same principle used in conventional fluorescent tubes.

The typically small mass of a solid-state electronic lighting device provides for greater resistance to shock and vibration compared to brittle glass tubes/bulbs and long, thin filament wires. They also eliminate filament evaporation, potentially increasing the lifespan of the illumination device.

Solid-state lighting is often used in traffic lights and is also used frequently in modern vehicle lights, train marker lights, remote controls etc.

    

1970

    

  

  

    

        

  

  

A Light-Emitting-Diode lamp is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. Since the light output of individual light-emitting diodes is small compared to incandescent and compact fluorescent lamps, multiple diodes are used together. LED lamps can be made interchangeable with other types, but presently at a higher cost. Most LED lamps must also include internal circuits to operate from standard AC voltages. LED lamps offer long life and high efficiency, but initial costs are higher than that of fluorescent lamps.

    

1980

    

  

  

    

        

  

  

General purpose lighting requires white light. LEDs by nature emit light in a very small band of wavelengths, producing strongly colored light. The color is characteristic of the energy bandgap of the semiconductor material used to make the LED. To create white light from LEDs requires either mixing light from red, green, and blue LEDs, or using a phosphor to convert some of the light to other colors.

The first method (RGB-LEDs) uses multiple LED chips each emitting a different wavelength in close proximity to create the broad white light spectrum. The advantage of this method is the fact that one can adjust the intensities of each LED to "tune" the character of the light emitted. The major disadvantage is the high manufacturing cost, which is probably most important in commercial success.

The second method, phosphor converted LEDs (pcLEDs) uses a single short wavelength LED (usually blue or ultraviolet) in combination with a phosphor, which absorbs a portion of the blue light and emits a broader spectrum of white light. (The mechanism is similar to the way a fluorescent lamp produces white light from a UV-illuminated phosphor.) The major advantage here is the low cost, while the disadvantage is the inability to fine tune the character of the light without completely changing the phosphor layer. So while this will not yield high CRI (color rendering index) values without sacrificing some other performance property, the low cost and adequate performance makes it the most suitable technology for general lighting today.

To be useful as a light source for a room, a number of LEDs must be placed close together in a lamp to add their illuminating effects. This is because an individual LED produces only a small amount of light, thereby limiting its effectiveness as a replacement light source. If white LEDs are used, their arrangement is not critical for color balance. When using the color-mixing method, it is more difficult to generate equivalent brightness when compared to using white LEDs in a similar lamp size. Furthermore, degradation of different LEDs at various times in a color-mixed lamp can lead to an uneven color output. LED lamps usually consist of clusters of LEDs in a housing with both driver electronics, a heat sink and optics.

    

1990

    

  

  

    

        

  

  

LED lamps are used for both general lighting and special purpose lighting. Where colored light is required, LEDs come in multiple colors, which are produced without the need for filters. This improves the energy efficiency over a white light source that generates all colors of light then discards some of the visible energy in a filter.

White-light light-emitting diode lamps have the characteristics of long life expectancy and relatively low energy consumption. The LED sources are compact, which gives flexibility in designing lighting fixtures and good control over the distribution of light with small reflectors or lenses. LED lamps have no glass tubes to break, and their internal parts are rigidly supported, making them resistant to vibration and impact. With proper driver electronics design, an LED lamp can be made dimmable over a wide range; there is no minimum current needed to sustain lamp operation. LEDs using the color-mixing principle can produce 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. LED lamps contain no mercury.

    

2000

    

  

  

    

        

  

  

However, some current models are not compatible with standard dimmers. It is not currently economical to produce high levels of lighting. As a result, current LED screw-in light bulbs offer either low levels of light at a moderate cost, or moderate levels of light at a high cost. In contrast to other lighting technologies, LED light tends to be directional. This is a disadvantage for most general lighting applications, but can be an advantage for spot or flood lighting.

    

2007

    

  

  

    

        

  

  

The Energy Independence and Security Act (EISA) of 2007 authorizes DOE to establish the Bright Tomorrow Lighting Prize competition. The legislation challenges industry to develop replacement technologies for the most commonly used and inefficient products, 60W incandescent lamps and PAR 38 halogen lamps. The L Prize specifies technical requirements for these two competition categories. Lighting products meeting the competition requirements would consume just 17% of the energy used by most incandescent lamps in use today. A future L Prize program announcement will call for development of a new 21st Century Lamp, as authorized in the legislation.

    

2008

    

  

  

    

        

  

  

In May 2008 the U.S. Department of Energy (DOE) announced details of the Bright Tomorrow Lighting Prize competition. The L Prize is the first government-sponsored technology competition designed to spur lighting manufacturers to develop high quality, high efficiency solid-state lighting products to replace the common light bulb. The competition will award cash prizes, and may also lead to opportunities for federal purchasing agreements, utility programs, and other incentives for winning products. Also in 2008, SSL technology advanced to the point that Sentry Equipment Corporation in Oconomowoc, Wisconsin, USA, was able to light its new factory almost entirely with LEDs, both interior and exterior. Although the initial cost was three times more than a traditional mixture of incandescent and fluorescent bulbs, the extra cost will be repaid within two years from electricity savings, and the bulbs should not need replacement for 20 years.

    

2009

    

  

  

    

        

  

  

The EISA legislation establishes basic requirements and prize amounts for each category. The legislation authorizes up to $20 million in cash prizes. On September 24 2009 the DOE announced that Philips was the first to submit lamps in the catogory to replace the of the standard 60W A-19 "Edison" light bulb.

    

2010