(PRWEB) March 29, 2005
Rough and compact in comparison to conventional light fixtures; LEDs can be used in different applications. As light emitting diodes are entering the lighting industry more and more each day, and most of the people are still not very familiar with LEDs advantages and (yes!) disadvantages, a brief info about these illuminating fixtures needed to be written, in order to help potential customers to get a fair idea about what they buy…
When people decide to buy a LED lamp they will consider what all that the manufacturers are telling about their products: saving energy and reducing costs, long life, no heat and so on. But is this true? Are LEDs really so efficient? What are the real advantages of such light sources? Where is it proper to use them and where not? In order to get these answers, lets take a look at LEDs real advantages.
Solid State Lighting (SSL) is what one may consider a new wave or a new generation in lighting technology as it brings a few advantages when we take into account the ways of procurement, installing, use and replacement of luminaries. SSL is supposed to be safer, environmental friendly, long lasting, flexible, energy efficient and cost-effective. When it comes to LEDs there are few characteristics to underline: a large choice of colours including RGB and a small size so they can be embedded into tiny spaces in appliances thus giving flexibility in designs for illumination and not only; light weight and low power consumption. These special characteristics are what manufacturers point out in most of the cases, but almost all of them avoid telling how exactly LEDs should be exploited to bring real advantages.
The constant competition between famous LED manufacturers like Nichia, Cree, Lumileds, Toyoda Gosei, General Electric, Osram and many more, leads to progress and one thing is certain: LEDs and LED fixtures are taking over the traditional lighting (that includes high intensity discharge lamps, fluorescent and incandescent sources) and new high performance light emitting diodes are constantly developed.
Solid State Lighting the New Generation of Lighting
Solid-State Lighting is the youngest lighting technology, and by now it is believed to be more efficient than incandescence and fluorescence. The efficiency is not related to the lm/W effectiveness, but this idea has a solid base if we consider that SSLs produce light at or near the visible spectrum as a result the emitted light can be utilized straight or with minor conversion. Fluorescent luminaries do not produce usable light directly in such light sources the root is UV produced by an ionised gas inside the tube. This is transformed to visible light by phosphors coated on the inside of the tube, phosphors that will absorb the ultraviolet rays.
On the other hand, incandescent lights spend most of the energy they require in generating heat only about 5% of the discharge being the light we see. LEDs convert approximately 25 to 35 % of the energy to light, while the rest is heat. So LEDs do produce heat, but the light they dispense is what experts call cold light light near the visible part of the spectrum.
The main challenge for LED manufacturers is the efficiency of light emitting diodes versus traditional lamps when used for illumination. In this case white light is needed and white LEDs were only recently developed and the question is if they will ever be fit to create lamps that give off bright light, natural in appearance and economic. At the moment there is no such thing as an inexpensive LED lamp for illumination because producers need to overcame a very important aspect: the cost per lumen. While traditional incandescent light bulbs cost about a dollar per kilolumen, LEDs cost about 200 or more.
Expenses need to be reduced if we consider that LEDs are also inefficient when it comes to performance measured in lumens per watt. Conventional sources are able to emit 10 to 100 lm/W while LEDs achieve only 25 lm/W producers do hope that by the end of 2007 they will be able to achieve 75 lm/W.
High power LEDs are presently developed but they do face other manufacturing problems related to the poor heat dissipation (which will decrease the LED life) and so on.
So when you consider purchasing LED lamps for illumination, think twice. LEDs are simply not ready (YET) to replace traditional lighting for all applications. A few years from now on maybe they will achieve the desired qualities, as science is constantly developing new items, each better than the previous ones. But nowadays LEDs cannot compete with traditional light fixtures when it comes to lumen output. The natural question that follows these affirmations is: than why are LEDs considered economic? Because, as a matter of fact, they are if used wisely.
In SSL, to manufacture light emitting diodes, there are used both organic and inorganic semiconductors, therefore we can split the light sources attained this way in two categories: LEDs inorganic semiconductors and OLEDs organic semiconductors.
Light emission from inorganic semiconductors was initially observed by Henry Joseph Round who was the first scientist to observe a phenomenon called electro luminescence in a piece of Silicon Carbide (SiC) in 1907. The research was soon abandoned because the emitted yellow light was too dim. In 1962 a team from General Electric conducted by Nick Holonyak demonstrated the first light emitting diode and only six years later commercial LEDs were introduced on the market as indicator lamps (655nm red – gallium arsenide phosphide GaAsP) by Monsanto and in electronic displays by Hewlett-Packard.
In the 1980s the use of Gallium Aluminium Arsenate Phosfide (GaAlAsP) led to the first generation of super bright LEDs, first in red, than yellow and finally green. Later on, in the 1990s, a combination of Indium Gallium Aluminium Phosphide (InGaAlP) was used to produce ultra bright LEDs red, orange, yellow and green.
Ultra bright blue Gallium Nitride (GaN) LEDs arrived in the mid 1990s, with Indium Gallium Nitride (InGaN) LEDs producing high-intensity green and blue shortly thereafter.
The blue chips were the base for white LEDs to obtain white the emitting blue chip is coated with fluorescent phosphors (one of the manufacturing procedures). The same procedure is used to create other colours such as aqua or pink.
So far is clear that in order to manufacture LEDs inorganic semiconductors are needed. The composition of an LED is quite simple: generally a square diode chip is encased in a special epoxy, plastic, resin or ceramic housing. This tiny chip is mounted in a cup that will mirror the light produced by the passage of electrons in the semiconductor central part via the conductor material. A typical LED has two pins one longer than the other. The longer pin is the anode, or the positive segment, while the short pin is the cathode.
The LED housing can have different sizes or shapes which, along with other factors such as the size of the LED chip and the distance between this one and the epoxy lens and the shape of the reflector cup, will determine the viewing angle of the emitted light beam.
The combination of chemical elements used to produce the diode chip, along with the energy expanded to generate each photon, determine the wavelength, therefore the colour of the light. LEDs are currently available in the entire spectrum starting with the near infrared to the recently produced ultraviolet.
LED light is generally monochromatic when only one chip is used. Multicolour LEDs are made by incorporating two or more different colour chips in the same epoxy package. Speaking about multi chip technology, another procedure of attaining white light is given by the three-chip technique in which case white light is a mixture of the three primary colours: red, green and blue, blended in the right percentage.
The red, green and blue chips are mounted in the same package but can be individually controlled thus allowing different colour mixtures and the creation of other colours. RGB LEDs are used more and more today in the entertainment industry due to their ability to mix colours and create different light effects.
Super Flux LEDs
The four-pin design gives Super Flux LEDs a very important advantage over the traditional two-pin light emitting diodes: neither shock nor vibration will harm the LED or disconnect it from the electrical contact. The pins of the two-pin LEDs can easy brake when employed in items that are often exposed to heavy shock.
Another advantage given by super flux LEDs is the low thermal resistance. Mostly super flux LEDs are believed to have the lowest thermal resistance available for a through-hole light emitting diode, due to their large lead-frame design a very good feature for high performance applications.
These LEDs are also known under other names: Spider LEDs or Piranha LEDs and they give a fine flux and intensity needed for the printed circuit board platform. This quality allows the creation of robust light fixtures with a low system cost while using average assembly equipment. The choice of viewing angles increases also the number of possible applications: from automotive to spectacular lighting designs, basically there is no LED application where these products cannot fit.
It is commonly stated that LEDs last more than 50,000 hours, and some manufacturers affirm that LEDs can last up to 100,000 operating hours. The main problem is that LEDs do not simply stop working. Rated life cannot be measured as we do with traditional lamps. In fact no one stood near some LEDs in a laboratory and waited till one LED failed. Still, there are other ways to test the life of an LED. LEDs will last very long because there is no filament to brake. Instead of just failing they will gradually degrade in performance over time. High quality LEDs are predicted to still deliver more than 60% of the initial light intensity also after 50,000 continuous operating hours. When their presumed lifespan is over it is possible that they still emit some light. In order to keep an LED alive it is necessary to sink or to drive the heat away from the LED chip. Heat is one of the main reasons why LEDs fail.
LEDs themselves are evaluated for a life of thousands and thousands of hours, but this doesn’t ensure that the products manufactured with LEDs will last that long. Defective handling and soldering can simply kill LEDs. For instance if the current goes over the manufacturer endorsement the LEDs can become brighter, however the increased heat can shorten their life. Luminaries realized with LEDs require a good knowledge of the features light emitting diodes have, solid light technology expertise, engineering skills and a lot of creativity.
With the LED lifespan issue already clarified, and with the shadow tossed over their efficiency when it comes to cost per lumen, one might ask than why do people think LEDs are so great?
For the reason that they can already do things former light sources cannot!
So their size is small. That makes them extremely versatile and as a result they can be configured in different patterns to achieve any shape designers think of. In some applications hidden lights will create a mystical atmosphere or just give the impression of natural while, in fact, they are artificial means. Concealed soft lights are not only mysterious, but stimulate the subconscious and lead to meditation, relaxing the inner self, creating a sense of wonder. Being able to conceal LEDs where larger lamps cannot be hidden gives designers the possibility to develop compact light fixtures and signage items. To hide the light and create different patterns used to be difficult before LEDs.
Flexibility of shapes is not the main advantage is just one of the many. Choice of colours should be on the list. There are many colours available: red, orange, amber, green, yellow, cyan, violet, blue and white, as well as bi-colour LEDs, tri-colour LEDs and RGB LEDs. Fact is that LEDs in general do not require filters to generate coloured light. Deep colours can be produces monochromatic directly from the solid-state component. Being no filter needed to create the correct colour, no light is wasted, therefore no energy is lost.
The colour an LED has is influenced by the semiconductor material and not by the epoxy housing. Still the epoxy packages can be also coloured and available as diffused or transparent. Most of the LEDs are available in uncoloured housings which can be either milky or water clear.
RGB LEDs are yet the light emitting diodes that can give the users the largest amount of choices. Using the multi chip technology (as the bi and tri-colour LEDs) their functionality is still increased due to some very important features. First of all, as already mentioned in the previous chapter, each LED chip is individually controlled, so by combining their emissions millions of colours can be created with no need of diffusing filters as used for other light sources mainly to give the emitted light the appearance of homogeneous.
This leads us to another very important advantage LEDs show over the traditional lamps: control. There are many important aspects to underline if we speak about how to control LEDs and this is the main advantage.
RGB technology is revolutionizing the lighting industry at the very moment. Architecture illumination has new meanings and this happens due to the dynamic light effects that can be controlled in so many different ways: from the simple touch of a button to more complicated means such as DMX 512 light mixing consoles. Infinite varieties of effects are available for so many applications that is almost hard to create a fair list: wall washers, pools and fountains illumination, application in special industrial environments, home and work luminaries, entertainment light effects, signage, automotive, city beautifications, medical appliances and much, much more. Light designers know that the use of LED lighting systems makes possible an ample colour scale with hues almost impossible to achieve with the existing fixtures. They also know that they can control the LED light sources and create countless special effects whether this means an adjustable lamp of a single colour or a source able to produce digitally any colour in the spectrum. Controlling the emitted light and colour will not affect the CRI (Colour Rendering Index) because, unlike the other illumination technologies, with LEDs the CRI is not intensity dependent.
When it comes to control, lets not forget a very important feature LEDs have: they are fully dimmable (from 100% to 0%) thus making possible the optimisation of the light intensity to be appropriate for every employment of the LED source. The dimming is done through PWM drivers (pulse width modulation via digital control which is the most commonly used method) and the emitted colour is independent of the set intensity. Nothing happens to the LEDs wavelength while dimming, the colour remains the same, only the brightness changes. This goes also for the situation when an LED grows old and looses efficiency. Dimming will not shorten the life of an LED, as it happens with repeatedly dimmed fluorescent tubes, on the contrary: it might extend it because it reduces the operating temperature inside the light source.
Still speaking about control, a very important aspect is that LEDs have almost instant turn on times, with no flickering and an immediate arriving at the emitted wavelength that makes LEDs perfect for security applications, including emergency lighting and traffic signage. This feature is as important it the RGB colour changing systems for dynamic effects and the synchronization of the LEDs in the system.
Another important feature a manufacturer will underline about LEDs is that they are low-voltage light sources. This feature is the guilty one when people rush into buying LEDs as economic means of illumination. Indeed, taken individually, LEDs used for illumination need between 2V to 4V DC (direct current), but if the LEDs are connected in series to form an array the required voltage increases according to the number of LEDs. In short: one LED doesnt consume a lot, but many of these tiny devices do. Generally single colour LED products draw less than 5 watts, some less than a watt. Safety lighting (exit signs) and emergency lighting are using more and more light sources based on LED technology, thanks to the energy savings (perfect for battery back-up systems), less maintenance and longer life than conventional lamp technology.
In order to get the proper amount of direct current LEDs need a device able to convert the incoming AC power to the required DC voltage. Another aspect is that LEDs must be protected against the voltage fluctuations during operation. This is why my-tronic GmbHs engineers (and all the LED engineers, of course) use special drivers to convert different voltages in low-voltage DC power and to protect the LEDs from line-voltage fluctuations. The LED drivers may be constant voltage types (such as 10V, 12V) or constant current types (350mA, 700mA) and can run specific LED arrays or ordinary LEDs. It really depends on the application where these light sources are needed. The drivers are rated for a maximum load that must be respected. And also the LEDs are very vulnerable. For instance if a wrong voltage driver is used to operate an array, the device will either not lit up or it will run at higher currents than projected. For example a 12V driver used for a 10V LED array shortens significantly the life of the device.
Some other significant advantage LEDs have over traditional light sources is the environment friendliness. There are a few important aspects to underline:
LEDs are made from non toxic materials, unlike the fluorescent tubes. There is no mercury in the source so the pollution danger is inexistent. Besides, LEDs are recyclable.
If not produced as IR LEDs, these diodes emit electromagnetic energy in the visible part of the spectrum. Incandescent bulbs emit a lot of energy in the invisible part of the spectrum the infrared part, which, although it cannot be seen, it can be felt as heat. With virtually no heat emission in the light beam, LEDs are perfect for applications where incandescent bulbs may constitute a safety hazard or may just damage sensitive materials (food for instance). Still, as already explained, LEDs are getting hot it is only the emitted light which is cold. What is getting hot is the diode chip itself, because, unlike what manufacturers usually say, LEDs convert only up to 25% of the energy they need into light the rest, as with incandescent sources, is lost. But 25% is still better than only 5%, and on a long term this is how the savings are calculated. Infrared increases air conditioning costs, decreases environmental comfort, and when reflected off reading surfaces increases eyestrain. Lack of infrared solves these problems. LEDs provide cool light and safe-to-touch illumination fixtures.
If not produced as UV LEDs, or white LEDs created with the UV technology, light emitting diodes contain no ultraviolet. Ultraviolet light can damage materials, cause colour changes and harm living organisms in many ways. For example plants overexposed to UV light reduce size and are more susceptible to specific diseases. LED technology has eliminated the harmful components from the light sources. In museums and other applications where UV may cause a lot of damage, LEDs are the lights saving the day.
The energy savings as part of the environmental friendliness issue are explained by the technology used to produce light: LEDs place light exactly where needed. LEDs produce luminosity through a straight, electricity-to-light conversion, and because they are directional light sources a photon should never be wasted. Standard sources such as incandescent, halogen, or fluorescent lights are omni directional (emitting light in all directions). To lead the beam to a specific item desired to be illuminated, light has to be redirected using secondary optics or reflectors and when a light beam is reflected it looses some of its intensity, resulting in an energy waste.
To be able to direct the light where needed relates to another important attribute of LEDs: choice of viewing angles. The LED housing can have different sizes or shapes which, along with other factors such as the size of the LED chip and the distance between this one and the epoxy lens and the shape of the reflector cup, will determine the viewing angle of the emitted light beam. Basically LEDs can come in any viewing angle up to 180°, unlike an omni directional lamp, which has a 360° light emission.
And lets not forget LEDs ability to cold start. LEDs love the cold, down to 40°C. Other light sources do not operate proper in cold environments without expensive drivers required to enable ignition at low temperatures. With this quality LEDs are on/off controllable without specially designed circuitry thus engineers can simplify the system design while reducing the costs for special drivers.
Nowadays there are already available on the market LED lamps with an efficacy of 60 lm/W. (Enlux Lighting, winner of the 2004 edition of Lightfairs Energy and LED Lamp Awards, showcased a new LED floodlight that generates light equal to a 60-watt incandescent flood, while utilizing one-third of the power and offering longer life. ). We can conclude that LED technology evolves on the right path.
SSL is still a young technology and LEDs are still what one may call pioneers. So it is expected that we will soon witness spectacular improvements, as LEDs will become increasingly brighter and this new technology will probably develop the best light source ever the potential LEDs have is huge. There are so many lighting companies researching and testing these products that keeping up to date and dealing with SSL-technology can be considered more than just a full time job.
With so many qualities and advantages, one may ask still: why do LEDs still cost so much?
First of all because they are a new technology and the production costs are still high. These costs will decrease in time as the manufacturers improve their production facilities. Currently a lot of research and development is going on in the world of LEDs, as the quest for brighter and more efficient sources is not over. Still, although they do cost a lot when purchased, on the long run LEDs are significantly inexpensive if the maintenance, lifespan and energy savings are taken into account. Yet the cost and the amount of LEDs necessary to match or enhance fluorescent lighting points up that there are developments to be made on the intensity and costs of the LEDs. Within the next 2 to 4 years, the industry expects to be competitive.
Are LEDs prepared to come into the light field of regular lamps? The answer still oscillates between yes and no. In spite of all the pros and contras LEDs are a young lighting technology. They can still be costly and the light amount needed to replace most traditional lamps simply isnt here up till now.
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