Αν είστε ιδιώτης ή επιχειρηματίας ή αν ανήκετε στο δημόσιο τομέα,
μείωστε δραστικά τους λογαριασμούς του ηλεκτρικού ρεύματος
τοποθετώντας στις εγκαταστάσεις σας:
Λαμπτήρες Εξοικονόμησης Ενέργειας LED τέταρτης γενιάς
ΑΓΟΡΑΣΤΕ ΑΠΟ ΤΟ ESHOP MAS – http://www.smart-led.gr
Η αναγκαιότητα της εξοικονόμησης ενέργειας σήμερα
Στη σημερινή εποχή, όπου η ολόκληρη ανθρωπότητα βρίσκεται κάτω από την πίεση σοβαρότατων προβλημάτων όπως είναι η καταστροφή του περιβάλλοντος και η διεθνής οικονομική κρίση, η εξοικονόμηση ενέργειας είναι ιδιαίτερα σημαντική, επειδή επιτυγχάνει τα εξής:
Μείωση του κόστους λειτουργίας στις επιχειρήσεις
Εξοικονόμηση χρημάτων στα νοικοκυριά
Μείωση των ρύπων που εκλύονται στο περιβάλλον κατά την παραγωγή της ηλεκτρικής ενέργειας.
Τα οφέλη και τα πλεονεκτήματα των λαμπτήρων LED
Η Smart Technical Solutions προτείνει μία σειρά από λύσεις εξοικονόμησης ενέργειας, μία από τις οποίες είναι η αντικατάσταση των ενεργοβόρων λαμπτήρων παλαιάς τεχνολογίας με λαμπτήρες LED τέταρτης γενιάς, οι οποίοι παρέχουν τα εξής οφέλη:
Εξοικονομούν ενέργεια από 70% έως 95%.
Έχουν διάρκεια ζωής από 30.000 έως 50.000 ώρες.
Εγγύηση δωρεάν αντικατάστασης από 1 έως 5 έτη.
Χρόνος απόσβεσης από 6 μήνες έως 2 έτη.
Εντελώς αβλαβείς για την υγεία, απόλυτα φιλικοί προς το περιβάλλον.
Μεγαλύτερη φωτεινότητα από τους κοινούς λαμπτήρες LED κατά 25-50%.
Διατίθενται σε μεγάλη ποικιλία χρωμάτων (warm, daylight, cool κ.ά.)
Είναι συμβατοί με ρεοστάτη (dimmer).
Μεγάλη ποικιλία, αντικαθιστούν όλους σχεδόν τους τύπους λαμπτήρων.
Σταθερή απόδοση για όλα τα χρόνια λειτουργίας τους (σε αντίθεση με άλλους τύπους).
Εύκολη τοποθέτηση, χωρίς τη μετατροπή που απαιτούσαν οι προηγούμενες γενιές LED.
Καταργούν το κόστος της συχνής αντικατάστασης λαμπτήρων σε δυσπρόσιτα σημεία.
Ιδανική λύση και για φωτισμό δρόμων, γήπεδα, προβολείς, ισχύς λαμπτήρα μέχρι 2.500W.
Ακίνδυνοι λόγω χαμηλής τάσης: 9-12 Volt, με εξαίρεση των φορτηγών, που είναι 24 βολτ
Μεγάλη γωνία φωτισμού (ευρεία δέσμη φωτός), έως 150 μοίρες.
Δεν διατίθενται σε καταστήματα λιανικής πώλησης.
Αναλυτική παρουσίαση των πλεονεκτημάτων θα βρείτε στο αγγλικό κείμενο πιο κάτω.
Χαμηλό κόστος και σύντομος χρόνος απόσβεσης
Η τεχνολογία LED (Light Emitting Diode = ημιαγωγός εκπομπής φωτός) στα πρώτα της βήματα είχε υψηλό κόστος, ενώ οι λαμπτήρες ήταν ευπαθείς σε αυξομειώσεις τάσης και διαρκούσαν λιγότερες από 10.000 ώρες, ενώ η εξοικονόμηση ενέργειας που πετύχαιναν δεν ήταν θεαματική. Έτσι, είχαν εφαρμογή σε ειδικές μόνο περιπτώσεις.
Σήμερα, οι λαμπτήρες LED τέταρτης γενιάς (SMD LED) έχουν ξεπεράσει όλα αυτά τα προβλήματα και μπορούν πλέον να αντικαθιστούν σχεδόν όλους τους τύπους λαμπτήρων και η επένδυση να αποσβένεται μέσα σε 6 μήνες έως 2 έτη, με μόνη εξαίρεση τους λαμπτήρες φθορισμού, των οποίων ο χρόνος απόσβεσης συνήθως ξεπερνά τα 5 έτη και οι οποίοι εφαρμόζονται συνήθως για άλλους λόγους άσχετους με την εξοικονόμηση ενέργειας, που σε ορισμένες εφαρμογές εξαιτίας των ειδικών συνθηκών της εφαρμογής και απαιτήσεων του πελάτη μπορεί να είναι πολύ σημαντικοί (καλύτερη ποιότητα φωτισμού, δεν τρεμοπαίζουν, δεν προκαλούν παράσιτα και ηλεκτρομαγνητικά πεδία κ.ά.).
Ακόμα και σήμερα διατίθενται στην αγορά σε χαμηλές τιμές λαμπτήρες LED χωρίς προδιαγραφές, οι οποίοι έχουν μεγάλη ευπάθεια και δεν διαρκούν περισσότερα από δύο χρόνια. Οι λαμπτήρες LED της Smart Technical Solutions, αντίθετα, έχουν πιστοποιήσεις CE, RoHS, TUV, καθώς και πιστοποίηση από το Τμήμα Φωτομετρίας του Ε.Μ.Π. και πολλές ακόμα διεθνείς πιστοποιήσεις.
Λαμπτήρες LED: Η φιλική λύση για τον άνθρωπο και το περιβάλλον
Δεν επιβαρύνουν με CO2 το περιβάλλον.
Είναι πλήρως ανακυκλώσιμοι.
Δεν περιέχουν επικίνδυνα τοξικά στοιχεία: υδράργυρος, κάδμιο, μόλυβδος
Μειώνουν και την κατανάλωση των κλιματιστικών, αφού δεν εκλύουν θερμότητα στο χώρο.
Εκπέμπουν μηδαμινή υπεριώδη ακτινοβολία
Παράγουν πολύ καλύτερη ποιότητα φωτός για το ανθρώπινο μάτι => εξαλείφουν προβλήματα οράσεως εξαιτίας κακού φωτισμού.
Δεν εκπέμπουν ακτινοβολία επικίνδυνη όπως οι CFL λαμπτήρες υδραργύρου που διαφημίζονται έντονα και πουλιούνται σε πολυ χαμηλές τιμές στα super-market.
Προσφέρουν άνετο και ξεκούραστο φωτισμό, με πολύ καλή ποιότητα χρώματος (CRI>80).
Οι λαμπτήρες πυρακτώσεως έχουν ήδη καταργηθεί στην Ευρωπαϊκή Ένωση και από το 2012 θα καταργηθούν και οι λαμπτήρες αλογόνου και φθορισμού ως επικίνδυνοι για την υγεία και επιβλαβείς για το περιβάλλον. Μελλοντικά είναι βέβαιο ότι θα καταργηθούν και οι CFL υδραργύρου για τον ίδιο λόγο, αφού ο υδράργυρος είναι άκρως επικίνδυνο τοξικό μέταλλο και όταν σπάσει ένας λαμπτήρας υδραργύρου, ελευθερώνεται στο χώρο με κίνδυνο κατάποσης από παιδιά κτλ. Επιπλέον, οι λαμπτήρες CFL υδραργύρου παράγουν κακή ποιότητα και στενή δέσμη φωτός, διατίθενται μόνο σε λευκό χρώμα, έχουν μόνο 8.000 ώρες διάρκεια ζωής, εκπέμπουν βλαβερή υπεριώδη (UV) ακτινοβολία και παράγουν Η/Μ πεδία.
Προφανώς τότε οι λαμπτήρες LED θα είναι μονόδρομος, αφού οι άλλοι σήμερα διαδεδομένοι τύποι λαμπτήρων θα έχουν καταργηθεί.
Εφαρμογές λαμπτήρων LED στην Ελλάδα
Στην Ελλάδα έχουν γίνει ήδη εκατοντάδες αντικαταστάσεις λαμπτήρων σε επαγγελματικούς χώρους και ιδιωτικές κατοικίες. Υπολογίζεται ότι η συνολική εξοικονόμηση ενέργειας που επιτυγχάνεται ετησίως στην Ελλάδα χάρη στους λαμπτήρες ξεπερνά τα 35.000.000€. Αυτό σημαίνει ότι ήδη η τεχνολογία LED έχει αρχίσει να παίζει ένα σημαντικό ρόλο στην οικονομία της χώρας, και σίγουρα πρόκειται να παίξει πολλαπλάσια σημαντικό ρόλο, όταν θα υιοθετηθεί από όλους τους μεγάλους καταναλωτές του ιδιωτικού και του δημόσιου τομέα. Κατάλογος των πιο σημαντικών εφαρμογών που έχουν γίνει από την Smart Technical Solutions είναι στη διάθεση κάθε ενδιαφερόμενου.
Είδη εγκαταστάσεων όπου μπορούν να τοποθετηθούν λαμπτήρες LED
Οι λαμπτήρες LED προσφέρουν σημαντική οικονομία σε όλες τις εγκαταστάσεις όπου γίνεται καθημερινά πολύωρη χρήση του ηλεκτρικού φωτισμού: από μία κατοικία μεσαίου μεγέθους μέχρι μία μεγάλη βιομηχανία. Ως εκ τούτου, το εύρος των εφαρμογών τους είναι τεράστιο. Πιο κάτω παραθέτουμε ενδεικτικά μερικά από τα είδη εγκαταστάσεων όπου συμφέρει να εγκαθίστανται λαμπτήρες LED σε αντικατάσταση των λαμπτήρων παλαιάς τεχνολογίας:
Εμπόριο – Υπηρεσίες
Και φυσικά πολλές ιδιωτικές κατοικίες. Τιμές, χρόνος παράδοσης, όροι συνεργασίας
Επικοινωνήστε με το 210-2282212.
Συνδυασμός με άλλες μεθόδους εξοικονόμησης ηλεκτρικής ενέργειας
Η Smart Technical Solutions προτείνει μία σειρά από μεθόδους εξοικονόμησης ηλεκτρικής ενέργειας, που όλες μαζί, αν εφαρμοστούν σε μία εγκατάσταση, μπορούν να επιτύχουν συνολική μείωση των λογαριασμών του ρεύματος ακόμα και 50%. Για περισσότερες πληροφορίες δείτε τη σελίδα Εξοικονόμηση ενέργειας ή επικοινωνήστε με το 210-2282212.
Τα πλεονεκτήματα των λαμπτήρων LED
Παραθέτουμε εδώ κείμενο του προμηθευτή μας στα Αγγλικά:
|Advantages of LED lights|
|LEDs offer numerous benefits due to their mode of operation:Energy Efficiency
LEDs are highly efficient. In traffic signal lights, a strong market for LEDs, a red traffic signal head that contains 196 LEDs draws 10W versus its incandescent counterpart that draws 150W. Various estimates of potential energy savings range from 82% to 93%. With the red signal operating about 50% of the day, the complete traffic signal unit is estimated to save 35-40%. It is estimated that replacing incandescent lamps in all of America’s some 260,000 traffic signals (red, green and yellow) could reduce energy consumption by nearly 2.5 billion kWh. At the end of 1997, more than 150,000 signals were retrofitted, almost all of them red.
In architectural applications, the greatest penetration of LEDs has been in exit signs, both new signs and retrofits. LED retrofit products, which come in various forms including light bars, panels and screw in LED lamps, typically draw 2-5W per sign, resulting in significant savings versus incandescent lamps with the bonus benefit of much longer life, which in turn reduces maintenance requirements. Some of these products are designed specifically for either on-face or two-face exit signs. Many new LED exit signs are also available, including edge-lit designs. LED products currently make up about 50% of the exit sign market. A study conducted by the Lighting Research Center in 1998 found that about 80% of new exit signs being sold in the U.S. utilize LEDs. Note that most retrofits are restricted to use in stencil-type signs versus panel-type signs.
Some LEDs are projected to produce a long service life of about 100,000 hours. For this reason LEDs are ideal for hard-to-reach/maintain fixtures such as exit sign lighting and, combined with its durability, pathway lighting. This service life can be affected by the application and environmental factors, including heat and if being overdriven by the power supply.
Range of Colors
LEDs are available in a range of colors (see above), including white light. White light can also be produced through color mixing of red, blue and green LEDs. In addition, through the innovative combination of various-colored LEDs, dramatic color-changing effects can be produced from a single fixture through dynamic activation of various sets of LEDs. Manufacturers such as Color Kinetics offer fixtures that employ this principle. Color Kinetics offers track, theatrical, underwater, outdoor and other fixtures utilizing variable-intensity LEDs that can provide more than 16.7 million colors, including white light. These fixtures can be individually controlled via a PC, DMX controller or proprietary controller to generate effects including fixed color, color washing, cross fading, random color changing, strobing and variable strobing.
Dr. Nadarajah Narendran of the Lighting Research Center is doing some exciting research on the use of colored LEDs in retail display lighting. Preliminary research suggests that using colored LED background lighting combined with spot lighting on merchandise may improve energy efficiency and reduce maintenance costs while catching the eye of the consumer in a fresh manner.
No UV Emissions/Little Infrared
LEDs produce no UV radiation and little heat, making them ideal for illuminating objects, such as works of art, that are sensitive to UV light.
LEDs are highly rugged. They feature no filament that can be damaged due to shock and vibrations. They are subject to heat, however, and being overdriven by the power supply.
Small Size/Design Flexibility
A single LED is very small and produces little light overall. However, this weakness is actually its strength. LEDs can be combined in any shape to produce desired lumen packages as the design goals and economics permit. In addition, LEDs can be considered miniature light fixtures; distribution of light can be controlled by the LEDs’ epoxy lens, simplifying the construction of architectural fixtures designed to utilize LEDs. A controller can be connected to an LED fixture to selectively dim individual LEDs, resulting in the dynamic control of distribution, light output and color. Finally, DC power enables the unit to be easily adaptable to different power supplies.
The other benefits of LEDs include:
- Lights instantly
- Can be easily dimmed
- Silent operation
- Low-voltage power supply (increased safety)
Περισσότερες πληροφορίες για την τεχνολογία LED
Παραθέτουμε εδώ κείμενο του προμηθευτή μας στα Αγγλικά:
A light-emitting-diode (LED), is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction in a solid state material.
LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. An LED is usually a small area (less than 1 mm2) light source, often with optics added directly on top of the chip to shape its radiation pattern and assist in reflection. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet. Besides lighting, interesting applications include using UV-LEDs for sterilization of water and disinfection of devicesand as a grow light to enhance photosynthesis in plants.
Discoveries and early devices
The first known report of a light-emitting solid-state diode was made in 1907 by the British experimenter H. J. Round of Marconi Labs when he noticed electroluminescence produced from a crystal of silicon carbide while using a cat’s-whisker detector. Russian Oleg Vladimirovich Losev independently created the first LED in the mid 1920s; his research, though distributed in Russian, German and British scientific journals, was ignored and no practical use was made of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using GaSb, GaAs, InP, and Ge-Si alloys at room temperature and at 77 kelvin.
In 1961, experimenters Bob Biard and Gary Pittman working at Texas Instruments, found that gallium arsenide gave off infrared radiation when electric current was applied. Biard and Pittman were able to establish the priority of their work and received the patent for the infrared light-emitting diode.
The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. He later moved to the University of Illinois at Urbana-Champaign. Holonyak is seen as the “father of the light-emitting diode”. M. George Craford, a former graduate student of Holonyak’s, invented the first yellow LED and 10x brighter red and red-orange LEDs in 1972. Up to 1968 visible and infrared LEDs were extremely costly, on the order of US $200 per unit, and so had little practical application. The Monsanto Corporation was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced light-emitting diodes in 1968, initially using GaAsP material supplied by Monsanto. The technology proved to have major applications for alphanumeric displays and was integrated into HP’s early handheld calculators.
The first commercial LEDs were commonly used as replacements for incandescent indicators, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches (see list of signal applications). These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, while maintaining the efficiency and the reliability to an acceptable level. The invention and development of the high power white light LED led to use for illumination (see list of illumination applications).
Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with increasing power output, it has become increasingly necessary to shed excess heat in order to maintain reliability, so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs.
The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation and was based on InGaN borrowing on critical developments in GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN which were developed by Isamu Akasaki and H. Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs demonstrated a very impressive result by using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs) LED. The existence of blue LEDs and high efficiency LEDs quickly led to the development of the first white LED, which employed a Y3Al5O12:Ce, or “YAG”, phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white. Nakamura was awarded the 2006 Millennium Technology Prize for his invention.
The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s, in a similar way to Moore’s law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. This trend is normally called Haitz’s Law after Dr. Roland Haitz.
Like a normal diode, the LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.
LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.
The refractive index of most LED semiconductor materials is quite high, so in almost all cases the light from the LED is coupled into a much lower-index medium. The large index difference makes the reflection quite substantial (per the Fresnel coefficients). The produced light gets partially reflected back into the semiconductor, where it may be absorbed and turned into additional heat; this is usually one of the dominant causes of LED inefficiency. Often more than half of the emitted light is reflected back at the LED-package and package-air interfaces.
The reflection is most commonly reduced by using a dome-shaped (half-sphere) package with the diode in the center so that the outgoing light rays strike the surface perpendicularly, at which angle the reflection is minimized. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should also match the index of the semiconductor, to minimize back-reflection. An anti-reflection coating may be added as well.
The package may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted.
Other strategies for reducing the impact of the interface reflections include designing the LED to reabsorb and reemit the reflected light (called photon recycling) and manipulating the microscopic structure of the surface to reduce the reflectance, by introducing random roughness, creating programmed moth eye surface patterns. Recently photonic crystal have also been used to minimize back-reflections. In December 2007, scientists at Glasgow University claimed to have found a way to make LEDs more energy efficient, imprinting billions of holes into LEDs using a process known as nanoimprint lithography.
Efficiency and operational parameters
Typical indicator LEDs are designed to operate with no more than 30–60 milliwatts [mW] of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.
One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficiency of 18–22 lumens per watt [lm/W]. For comparison, a conventional 60–100 W incandescent lightbulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W. (The luminous efficiency article discusses these comparisons in more detail.)
In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to provide 24 mW at 20 milliamperes [mA]. This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006 they demonstrated a prototype with a record white LED luminous efficiency of 131 lm/W at 20 mA. Also, Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents. Nichia Corporation has developed a white light LED with luminous efficiency of 150 lm/W at a forward current of 20 mA.
It should be noted that high-power (≥ 1 W) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA. The highest efficiency high-power white LED is claimed by Philips Lumileds Lighting Co. with a luminous efficiency of 115 lm/W (350 mA).
Cree issued a press release on November 19, 2008 about a laboratory prototype LED achieving 161 lumens/watt at room temperature. The total output was 173 lumens, and the correlated color temperature was reported to be 4689 K.
Ultraviolet and blue LEDs
Blue LEDs are based on the wide band gap semiconductors GaN (gallium nitride) and InGaN (indium gallium nitride). They can be added to existing red and green LEDs to produce the impression of white light, though white LEDs today rarely use this principle.
The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride LED) at RCA Laboratories. However, these devices had too little light output to be of much practical use. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping by Isamu Akasaki and Hiroshi Amano (Nagoya, Japan) ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated through the work of Shuji Nakamura at Nichia Corporation.
By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaN aluminium gallium nitride of varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, as opposed to alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350–370 nm. Green LEDs manufactured from the InGaN-GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems.
With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 247 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LEDs emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices.
Wavelengths down to 210 nm were obtained in laboratories using aluminium nitride.
While not an LED as such, an ordinary NPN bipolar transistor will emit violet light if its emitter-base junction is subjected to non-destructive reverse breakdown. This is easy to demonstrate by filing the top off a metal-can transistor (BC107, 2N2222 or similar) and biasing it well above emitter-base breakdown (≥ 20 V) via a current-limiting resistor.
White light LEDs
There are two ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit three primary colors – red, green, and blue, and then mix all the colors to produce white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works.
White light can be produced by mixing differently colored light, the most common method is to use red, green and blue (RGB). Hence the method is called multi-colored white LEDs (sometimes referred to as RGB LEDs). Because its mechanism is involved with sophisticated electro-optical design to control the blending and diffusion of different colors, this approach has rarely been used to mass produce white LEDs in the industry. Nevertheless this method is particularly interesting to many researchers and scientists because of the flexibility of mixing different colors. In principle, this mechanism also has higher quantum efficiency in producing white light.
There are several types of multi-colored white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different approaches include color stability, color rendering capability, and luminous efficiency. Often higher efficiency will mean lower color rendering, presenting a trade off between the luminous efficiency and color rendering. For example, the dichromatic white LEDs have the best luminous efficiency (120 lm/W), but the lowest color rendering capability. Oppositely although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficiency. Trichromatic white LEDs are in between, having both good luminous efficiency (>70 lm/W) and fair color rendering capability.
What multi-color LEDs offer is not merely another solution of producing white light, but is a whole new technique of producing light of different colors. In principle, all perceivable colors can be produced by mixing different amounts of three primary colors, and this makes it possible to produce precise dynamic color control as well. As more effort is devoted to investigating this technique, multi-color LEDs should have profound influence on the fundamental method which we use to produce and control light color. However, before this type of LED can truly play a role on the market, several technical problems need to be solved. These certainly include that this type of LED’s emission power decays exponentially with increasing temperature, resulting in a substantial change in color stability. Such problem is not acceptable for industrial usage. Therefore, many new package designs aiming to solve this problem have been proposed, and their results are being reproduced by researchers and scientists.
Phosphor based LEDs
This method involves coating an LED of one color (mostly blue LED made of InGaN) with phosphor of different colors to produce white light, the resultant LEDs are called phosphor based white LEDs. A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively increasing the color rendering index (CRI) value of a given LED.
Phosphor based LEDs have a lower efficiency than normal LEDs due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. However, the phosphor method is still the most popular technique for manufacturing high intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high intensity white LEDs presently on the market are manufactured using phosphor light conversion.
The greatest barrier to high efficiency is the seemingly unavoidable Stokes energy loss. However, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. The efficiency can for instance be increased by adapting better package design or by using a more suitable type of phosphor. Philips Lumileds patented conformal coating process addresses for instance the issue of varying phosphor thickness, giving the white LEDs a more homogeneous white light. With development ongoing the efficiency of phosphor based LEDs is generally increased with every new product announcement.
Technically the phosphor based white LEDs encapsulate InGaN blue LEDs inside of a phosphor coated epoxy. A common yellow phosphor material is cerium-doped yttrium aluminum garnet (Ce3+:YAG).
White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. However, the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness. Another concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.
Other white LEDs
Another method used to produce experimental white light LEDs used no phosphors at all and was based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emitted blue light from its active region and yellow light from the substrate.
Organic light-emitting diodes (OLEDs)
If the emitting layer material of the LED is an organic compound, it is known as an Organic Light Emitting Diode (OLED). To function as a semiconductor, the organic emitting material must have conjugated pi bonds. The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs.
Compared with regular LEDs, OLEDs are lighter, and polymer LEDs can have the added benefit of being flexible. Some possible future applications of OLEDs could be:
OLEDs have been used to produce visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players. Larger displays have been demonstrated, but their life expectancy is still far too short (<1,000 hours) to be practical.
Today, OLEDs operate at substantially lower efficiency than inorganic (crystalline) LEDs.
Quantum Dot LEDs (experimental)
A new technique developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs.
Quantum dots are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering white LEDs. Quantum dot LEDs are available in the same package types as traditional phosphor based LEDs.
Advantages of using LEDs
The many application of LEDs are very diverse but fall into three major categories: Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning. Illumination where LED light is reflected from object to give visual response of these objects. Finally LEDs are also used to generate light for measuring and interacting with processes that do not involve the human visual system.
Indicators and signs
White LED module
Light can be used to transmit broadband data, which is already implemented in IrDA standards using infrared LEDs. Because LEDs can cycle on and off millions of times per second, they can, in effect, become wireless routers for data transport. Lasers can also be modulated in this manner.
Light sources for machine vision systems
Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used to this purpose, and this field of application is likely to remain one of the major application areas until price drops low enough to make signaling and illumination applications more widespread. Barcode scanners are the most common example of machine vision, and many inexpensive ones used red LEDs instead of lasers.
LEDs constitute a nearly ideal light source for machine vision systems for several main reasons: