LEDs’ Real Advantages
Solid State Lighting – the New Generation of Lighting Manufacturing LEDs, Standard LEDs, Super Flux LEDs, LEDs’ Lifetime, LEDs’ Advantages
(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, let’s 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.
Manufacturing LEDs
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 1990’s, 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.
Standard LEDs
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.
LEDs’ Lifetime
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, let’s 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 doesn’t 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 GmbH’s 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 let’s 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 Lightfair’s
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 isn’t here up till now.
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