14-08-2013, 03:48 PM
HARNESSING PHOTONICS FOR LIGHTING
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INTRODUCTION
Photonics as per dictionary is “a branch of electronics that deals with devices for emitting, modulating, transmitting and sensing light”. However, Photonics has established itself beyond the realm of electronics, as one of the new branches of science and technology. Photonics, as we understand today, is the technology of generating and harnessing light and other forms of radiant energy whose quantum unit is photon. It is the technology for generating photons, controlling photons, detecting photons and utilizing photons for the progress of society and civilization.
PHOTONICS FOR LIGHTING APPLICATIONS
In the area of lighting and illumination technology, the application and progress of photonics is path breaking though not that spectacular as in communication technology. However, there are enough indications that the photonics technology is going to replace many of the present day applications of conventional lighting and illumination technology in near future. There are three main products of photonics technology that demand attention for lighting applications. These are (i) light emitting diode (ii) the lasers and (iii) the optical fiber. At the outset it is safe to comment that the full potential of all three major product of photonics are yet to be exploited fully in lighting applications at the present stage. However, each of these has shown enough potential for exploitation.
The light emitting diode (LED)
The first practical LED was developed in 1962 and was made of a compound semiconductor alloy, gallium arsenide phosphide, which emitted red light. The first commercial LEDs were introduced in 1968, at 0.001 lm/LED using GaAsP. Earlier LEDs were p-n junction devices constructed of gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP), or gallium phosphide (GaP). The junction is forward biased and when electrons cross the junction from the n- to the p-type material, the electron-hole recombination process produces photons in the IR or visible region through a process called injection electroluminescence. The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules. Only photons in a very narrow frequency range can be emitted by any material. The colour of the light emitted by a LED depends on the bandgap of the semiconductor is made of and is given by the relation λ = 1240 / (bandgap energy in eV), where λ is the wave length emitted
Organic Light Emitting Diode (OLED) Technology
An OLED uses a carbon based molecule that emits light when an electric current passes through it . The phenomenon known as photoluminescence was discovered by Kodak in 1985 and now OLED generates a 3B$ business. OLED displays can be produced in the same way an ink jet printer sprays ink into a sheet of paper, making manufacturing technology cheap and simple. OLEDs can be printed on flexible plastic sheets, thus opening a new vistas for product designer, for displays that can be rolled up or woven on fabric. OLEDs have distinct advantages over existing LCD flat panels in brightness, power efficiency, viewing angle and refresh rate. And they have come a long way when the glow from OLED would fede after 10 minutes.
It has been very recently reported that white light OLED can be made by mixing light of at least two different colours, one from the blue (short-wavelength) end of the spectrum and one from the red/yellow (long-wavelength) end. White light with two blue-light emitters has been attempted. Thin films from mixtures of two different organic molecules that glow blue when stimulated by an ultraviolet laser, are used. Such 'photoluminescence' often accompanies the electric-current-stimulated emission, or electroluminescence, needed for LEDs. The mixture produces white photoluminescence because it seems the two kinds of molecules exchange electrons when excited by ultraviolet light. This sharing of electrons creates a new light-emitting state with a broad band of emission wavelengths across the visible spectrum, which we perceive as white.
CONCLUSION
We have shown only three major applications of photonics in the area of lighting. There are enough scope of business and development activities in the area as the area is yet to mature into a fully grown industry. At the same time it must be mentioned that , there is no industry that can truly called photonics industry itself. In fact photonics germinates from the conglomeration of many technologies, which culminate to a single photonics product and photonics lighting is no exception.
The trend in industrial and research activities in photonics lighting are expected to center round the need for integration with other technologies. Making of photons, controlling photons, transmitting photons, catching photons and utilizing photons will be beyond the present imaginations and would encompass the areas of energy efficient sources to entertainment.