Over the past decades the lighting industry was shaped by rapidly evolving new lighting technologies and applications. LEDs (Light emitting diodes) are semiconductor devices that convert electricity into light. They have been in operation all around us since the late 1950s, initially being used as simple indicator light in electronic appliances. Their tiny size and low power consumption rendered them a very competent indicator, perfectly suitable for visual indication on particular points such as computers, digital clocks, radios or remote controls.
The developing race among manufacturers in LED technology, however, results nowadays in a rapidly growing potential of these small electronic devices. Over the past years the traditional concept of application underwent a transformation due to continuous material and semiconductor advancement. The significant improvement of visible brightness, form factor and switching response created a multiple of new and unique application possibilities and enabled a new category of lighting: these days LEDs process data, function as light source and can even display text, whole graphics and images when collected together. Recently developed white LED can be used for general lighting. Continuous improvements in LED lighting technology promises to not to only let LEDs replace the ordinary light bulb, but also to become the most common device to be utilized in today’s society.
What is the difference?
LEDs differ completely from other light sources (e.g. filament lamps, discharge lamps and fluorescent tubes), not only in size and renderings, but especially in regard to how they operate. The light emittance is initiated through an “electroluminescence injection’, a phenomenon first observed in 1907 by H. J. Round experimenting with Silicon Carbide. This means light is emitted through the release of energy during the exchange of positive and negative charged atoms. Conventional light bulbs, for instance, produce light through the heating of filament to the point where it gives off light, fluorescent light bulbs through excited atoms emitting light through fluorescence, or discharge lamps by applying a certain pressure on the mercury inside the light bulb.
How does it work?
LEDs are semiconductor devices that emit incoherent narrow-spectrum light in a specific color when electrically biased forward.
As indicated by its name, a LED is a light emitting diode, a most basic sort of semiconductor device in the electronic field; able to conduct electrical current in one direction. A LED consists of a chip comprising two semi-conducting materials, which are separated into two areas: the n-doped side (anode), where negatively-charged electrons move to a positively charged area, and the p-doped side (cathode), where positively-charged electrons move to the negative area. The transfer area between the positive and negative semi-conductor is called “p-n junction”. Once power is applied, electron-rich (/-deficient) particles are balanced and light arises due to the interface recombination process.
LED-lighting is also commonly called Solid State Lighting (SSL), since a diode is a solid state device with no moving mechanical parts involved. There are several benefits coming along with Solid State lighting devices such as their low power consumption, long lifetime and resulting maintenance costs, their vibrations resistance and no UV radiation, as well as their digital controllability and instant response.
For practical use, some types of LEDs are assembled onto printed circuit boards (PCBs), which in general are additionally equipped with electronic components to control the current flowing through the LED. Depending on the assembly of the LEDs onto the PCB, different types can be defined. Next to Radial LEDs (LEDs with legs that pass through holes on a PCB, fixed underneath the PCB via soldering) which are commonly used on LED screens, Surface Mount LEDs (commonly called LED SMD) are the most common and modern nowadays. Assembled directly onto the PCB, their size can range from small to large depending on usage and intended power. Unlike radial LEDs, SMDs normally do not have cover lenses but emit a more even light output on the surface.
First developed in the 1950s, LEDs were originally only available in infra-red. These LEDs were put to good use in remote controls, televisions and a few other appliances.
Between 1950 and 1990, Red, Green and Amber LEDs were developed - the mid 1990s saw the Blue LED come to light, from which white light could be produced by mixing red, blue and green (additive color mixing). Since the introduction of the Blue LED, their general light output has doubled approximately every two years.
Up to then, white light only could be produced by the combination of “rainbow” groups of three LEDs – red, green, and blue – yielding to each other, for receiving an overall white light.
During the last years, new white LEDs have become available by combining different phosphor types with a UV LED. This new method not only permits to create new white light source, but also enlarge the spectrum of RGB colors: even colors such as purple, orange or pink are now possible to create, setting no limits to the universe of color display.
Another revolutionary illuminant is the organic LED (OLED). Until today OLEDs are mainly used in displays of electric household appliances and mobile phones, but based on advanced researches OLEDs have the potential to be used for another generation of innovative lighting solutions in a few years. Generally organic LEDs are based on glass substrates. Further components are a luminiferous layer, the electric contacting and the casing. Operable prototypes show that it is possible to create a flexible light source based on ductile transparent substrates.
Continuous researches of materials resulted in the development of a number of organic material systems, in which light can be generated. These systems are classified into two groups, organic LEDs with small molecule chains (sm-OLEDs) and LEDs with large molecule chains, so-called polymers (pOLEDs). The two groups can be differed by the number of materials needed to create the luminiferous layer. The organic part of sm-OLEDs consists of four layers; however, p-OLEDs can reach the same functionality with only two layers.
Depending on the organic material used, each color of the visible spectrum can be created, including white light. The advantage of OLEDs is their ability to generate white light already in the organic layer by light interference. Using this method of light interference, white and colored OLEDs can be created, completely lucent when switched off. Manufacturing these kind of lucent OLEDs is very simple, but it is not possible to change the color of their light; the light can only be dimmed. The interference to white light allows the adjustment of the color temperature, which offers the opportunity to create color gradients.
An alternative for mixing white light is by mixing blue light of the organic layer and yellow light of the conversion luminescent material.
OLEDs offer a maximum flexibility in coloring and dimming, but their costs are still high.
As a result of the increasing demand for more efficient, flexible and creative lighting solutions in recent years, LED (Light Emitting Diode) lighting technologies have been evolving tremendously. Offering a convincing set of advantages including low energy consumption, high durability as well as the ability to generate a huge spectrum of different colors, LEDs present a viable alternative to conventional light sources and has become an attractive medium for numerous industries.
Consuming only 10 – 20% of the power required by regular lighting sources, LEDs are very energy efficient. Whilst, for instance, a regular traffic light containing an incandescent light bulb draws 150W, the application of LEDs reduces the energy consumption to 10W. This does not only allow tremendous energy cost savings, but also a reduction of the environmental impact of artificial lighting which has become a worldwide concern in recent years.
In contrast to conventional light bulbs which generally expire after 5,000 hours, the lifetime of LEDs ranges from 35,000 to more than 50,000 hours - this is equal to more than 51/2 years of continuous operation. Consequently, replacement costs of LEDs are reduced to a minimum for the customer.
Based on its advanced construction, LEDs are very durable: while regular light sources are very fragile and sensitive to shocks and vibrations, the encasement of high strength optical grade resin of LEDs renders them extremely resistant to outside influences. This robustness significantly reduces maintenance costs and makes LEDs highly suitable for most demanding installations indoors and outdoors. Due to their energy efficiency, long lifetime, and high durability, LEDs do not only operate on an environmentally friendly basis, but also reduce costs significantly. Despite the fact that the initial cost of LED bulbs is higher than that of incandescent or halogen light bulb, the long term savings certainly pay off.
Advantages for Design and Architecture
RGB LEDs can emit a wide range of different colors (up to 16.7 million) and can be used in conjunction with one another to create color changing effects. The application of a control system enables the user to define brightness, color and speed of color changing of an RGB LED. As they start instantly and react directly to control, they are ideal for quick, dynamic light scenes. The small size of a LED allows their manufacturing in a variety of shapes which renders them a flexible lighting source for every kind of application.
The LEDs' low voltage usage, the low level of generated heat, as well as the fact that they do not produce any UV radiation render LEDs not only a convenient and flexible lighting solution, but also a highly secure one. While conventional light sources frequently cannot be used for illuminating certain materials, LEDs are combinable with almost every type of material, offering its users an unlimited range of application possibilities.
LEDs are low energy products which reduce carbon emissions. As they contain no sulfurs or phosphors like other light sources, they are an eco-friendly product for disposal, contributing actively to the protection of the environment.
The rapid development of LEDs consisting of a continuously climbing light output, improvement of light efficiency and quality, increasing energy savings as well as shrinking cost, renders LED light bulbs the light source of the 21st century. Resulting in a strong market growth, LEDs are set to conquer the lighting industry.
From indication to Illumination:
Traffic lights, automotive, exit signs etc
Portable appliances, cell phones & PDAs
Direct view displays; video screens
Transportation: marine, auto, aviation etc.
Areas of application:
=SSL for small scale applications
White LEDs replacing conventional light bulbs
Areas of application:
=SSL for large scale applications
Nowadays, five major trends become apparent:
Broader use of LED-fixtures: especially the semi-professional market is characterized by an increased use of LED-fixtures. A growing ecological awareness and new environmental directives render LEDs the lighting solution of the new century: their longevity, low power consumption, high light output and low maintenance costs render them perfectly suitable for any lighting installation, no matter if short-term or permanent, large scale or small scale. Especially in applications located in hard-to-reach and thus difficult to maintain areas, such as recessed and angled spaces like high buildings, bridges etc. the longevity and durability of LEDs represent the solution. A strong development resulting in increasing performance and higher light-output will enlarge the application areas and design possibilities of LEDs.
Higher demand of interactive LED systems: Especially for the professional market, as lighting applications become more and more elaborate, the development of interactive and more efficient LED-systems are of great benefit. The usage of sensor systems (e.g. tracing motion, body heat, speed etc.) becomes more and more popular, rendering installations as flexible as never before. For instance, a regular public lighting system based on interactive LED lighting benefits not only of the increased energy saving potential and low maintenance costs of the LEDs, but also of even further cost savings due to the system’s capabilities such as creating “light on demand”: the sensor system, interacting with the public, can increase or decrease the amount of lights exactly to the amount of people, their movements or speed. Next to the cost reduction and energy efficiency, an added artistic value is also added to the lighting installation - creating a unique experience for the observer.
Penetration of the consumer market: LED lighting becomes more and more the focus of consumers and will enter everyday life in the near future. Low intensity LEDs can already be found in many sectors such as electronic equipment, toys, domestic appliances, traffic signal etc. In the future LEDs will play an increasing role for end-users, as the new technology of high power LEDs is on the advance. Due to increasing benefits such as energy efficiency, longevity, low maintaining costs as well as continuously decreasing acquisition costs, LEDs are attractive as never before for the residential market. LEDs are already used for decorative lighting and will in the near future replace some conventional light sources in everyday life.
Increasing use of White LEDs: The price/performance situation of white LEDs continues to improve and makes white LEDs more and more competitive to conventional white lighting sources. Compared to conventional light bulbs (e.g. incandescent lamp, discharge lamp), their extremely high light output and brightness, as well as their unique flexibility to adjust the color temperature of the white light output (ranging between 3000 and 7000K) render white LEDs the light bulb of tomorrow. White LED applications, for instance, will soon become one of the standard light sources for functional illumination, revitalizing central cities and encouraging high-density housing.
OLEDs on Advance: OLEDs are solid state devices made with organic material (OLED), handled as the next generation of LEDs. The latest organic light emitting diodes are more powerful, use less power, and are more efficient than conventional diodes and represent an alternative and still more ecological solution. Their unique variability in application due to their tiny size, extremely low heat emission and flexibility render them a perfect solution for advanced lighting applications - even on elastic surfaces like fabrics if produced with a high density.