Background

Solid-state lighting: the next generation of light sources for general illumination, from homes to commercial applications.

LEDs are the predestined lighting technology for a variety of applications: portable lights, lights for the workplace and reading lights, path lighting, as decorative lighting and for setting accents, lighting for show cases and objects as well as for light objects. In outdoor applications, LEDs provide the optimal solution for the bollard, curb and stairway lighting as well as for path lighting, orientation lighting and garden lights. Their low power is additionally conducive to photovoltaics, for example, as an energy autonomous lighting supply. Especially in architecture, colored LED lights are used to light up walls and parts of buildings. They are increasingly being used in the commercial area (for lighted text, show cases for promotional purposes.)

The power for many of the outdoor applications listed above can be supplied with photovoltaics. The energy efficiency of the LED is accommodating to a solar power supply. For both portable (luminous flux from a few lumens to c. 80 Lumen) and stationary applications (80-500 Lumen), photovoltaically supplied lighting solutions using LEDs can be realized.

What is SSL?
Lighting applications that use light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or light-emitting polymers are commonly referred to as solid-state lighting.
Unlike incandescent or fluorescent lamps, which create light with filaments and gases encased in a glass bulb, solid-state lighting consists of semiconductors that convert electricity into light.

LEDs have been around for a long time, but until recently they were used only in electronic devices as indicator lamps.

Through the technological developments in the last decade made it possible for LEDs to be used in signal devices, like traffic lights and exit signs, and in some limited illumination applications, such as flashlights. However, cutting-edge research now shows a bright future for solid-state lighting as the next generation of light sources for general illumination (from homes to commercial applications).

Solid-state lighting promises to change the way we light the world, yet much work and research are still needed. There are a lot of challenges and opportunities offered by solid-state lighting.

Why Solid-State Lighting?
Solid-state lighting is more and more used in a variety of lighting applications because it offers many benefits, such as:

• Long life
  LEDs can provide 50,000 hours or more of life, which can reduce maintenance costs. In comparison, an incandescent light bulb lasts approximately 1,000 hours.
• Energy savings
  Commercial white LEDs provide more than 100 lumens per watt, compared to 14-20 lumens per watt for incandescent lighting. LEDs are especially advantageous for colored lighting applications because filters are not needed.
• Better quality light output
  LEDs have no ultraviolet and infrared radiation.
• Intrinsically safe
  LED systems are low voltage and have a low temperature (<60C)

LED lighting systems have already proved to be very effective in indicator applications where brightness, visibility and long-life are important, such as in exit signs and traffic signals.

New uses for LEDs in the general illumination market include small-area lighting, such as task and under-shelf fixtures, decorative lighting, and pathway and step marking. As white LEDs become more powerful and effective, LEDs will be used in more general illumination applications, perhaps with entire walls and ceilings becoming the lighting system.

How LEDs Work >>

LEDs differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).
The specific wavelength or color emitted by the LED depends on the materials used to make the diode.

Red and amber LEDs are based on aluminum indium gallium phosphide (AlInGaP). Blue and green LEDs are made from indium gallium nitride (InGaN). "White" light is created by combining the light from red, green, and blue (RGB) LEDs or by coating a blue LED with yellow phosphor
Source: U.S. Department of Energy