Using solid state lighting

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[edit] Introduction

There are thousands of technological advances in our world that help thousands of people everyday. These technologies range from access to clean water all the way to keeping buildings lit at night. While these technologies are helpful to those that live in a developed country, there are many others around the world that do not have this opportunity. In underdeveloped countries, there are no lamps or lights that can be turned on to continue work inside and outside of the home. This leads to less productivity which could make or break a family. But with Light Emitting Diodes (LEDs) becoming more and more accessible, there is a new type of appropriate technology which could revolutionize the way that countries see light. Solid state lighting that uses LED lamps is being created to show countries a new way to look at light.

[edit] Defining Solid State Lighting (SSL)

Solid State lighting is different because instead of using gas or filaments to illuminate, it uses Organic light emitting diodes(OLED), Light Emitting Diodes (LED), and also polymer light-emitting diodes (OLED). In solid state lighting, electrons and holes are injected into a forward-biased semiconductor p-n junction; they recombine creating photons; the resulting photons are extracted from the chip; then the photons are either mixed with different-color photons from other LEDs, or are energy down-converted into a distribution of colors using phosphors or other down-conversion materials, with the colors chosen so as to create the appearance of white.

The reason for the name solid state simply means that the semiconductor is a block instead of some other device like a gas tube. Unlike traditional lighting, however, SSL creates visible light with reduced heat generation or parasitic energy dissipation. Also, the solid state helps it last longer and makes it a better investment.

[edit] Comparing other methods of Light

[edit] Fluorescent Bulbs

Fluorescent lamps are glass tubes that contain mercury vapor and argon gas. When electricity flows through the tube, it causes the vaporized mercury to give off ultraviolet energy. This energy then strikes phosphors that coat the inside of the lamp, giving off visible light.

While these are good sources of light, they are known to have flickering problems from time to time and have to be used properly in order to last long. Another big problem is individuals who are sensitive to light can have health problems from the slight amount of ultraviolet light being given off.

[edit] Incandescent Bulbs

Incandescent bulbs work via the element called tungsten, which is the coiled part at the top of the bulb. An electrical current passes through the filament which causes heating until it produces light. while these bulbs are easily reproduced and are cheap, they burn out quicker and use up a lot more energy then they give off.

this chart shows different forms of light and how they compare in Lu/W

Type Efficacy in lm / W
Incandescent 5 - 17
Halogen 16 - 24
CFL 45 -60
FL up to 100
Current generation LED's 26 - 70
Next generation LED's up to 150

[edit] Calculations Behind LED

The wavelength (and color) of light emitted in a radiative recombination of carriers injected across a p-n junction is determined by the difference in energy between the recombining electron-hole pair of the valence and conduction bands. The approximate energies of the carriers correspond to the upper energy level of the valence band and the lowest energy of the conduction band, due to the tendency of the electrons and holes to equilibrate at these levels. Consequently, the wavelength (l) of an emitted photon is approximated by the following expression:

                                  l = hc/Ebg

where h represents Planck's constant, c is the velocity of light, and Ebg is the band gap energy. In order to change the wavelength of emitted radiation, the band gap of the semiconducting material utilized to fabricate the LED must be changed. Gallium arsenide is a common diode material, and may be used as an example illustrating the manner in which a semiconductor's band structure can be altered to vary the emission wavelength of the device.[1] To see pictures of what LED lamps look like, look here You can see how each individual LED light fits into the shape of a lamp.

[edit] Benefits of Solid State Lighting

In times like these, scientists have been able to utilize LED lights for more than just everyday bulb replacements. With the people working for the Light Up the World Foundation, solid state lighting is now helping out thousands of people who don't have the proper means of getting artificial lighting. The foundation has been able to provide a simple technology using solid state lighting and LED lamps to under developed countries. Using a special design, the benefits of the lamps range from low maintenance to providing long lasting light. The reason this program is so beneficial is because having proper lighting will not only allow more work to be done to help families but to also provide protection to communities that are potentially dangerous at night. The lighting used by the foundation is fairly simple to set up and does not need any form of electricity to work, but instead uses solar photovoltaic panels. The foundation will provide a kit that gets sent to different countries in need and there can be assembled in the appropriate way. The best and most beneficial part of these systems is how positively they effect the environment. With low energy and very little pollution, they provide clean energy that can last up to a year without replacement.

[edit] Components Used

Light up the World uses the following components to create their solid state lighting kits:

  • Two Modular 1 Watt Luxeon WLED lamps Currently we use 1.5. Watt Lamps
  • 12 Volt 7 Ah Sealed Lead Acid Battery–Rechargeable maintenance free battery
  • 5 Watt Kyocera Solar Panel

[edit] Cost of Product

Light Up the World says that a $200 donation will provide light for one household. They also will work with people of the community who would be able to install the lights. LED lamps used in a conventional way like for homes or projects around the house can range from 30 to 80 dollars depending on size and power.[2]

[edit] Disadvantages of Solid State Lighting

  • LED lights are expensive because the market for them is not big enough to be mass producing them at a cheaper cost. Therefore, many shy away at switching their existing structures for new ones.
  • phosphors are used for there abilities to emit a broader spectrum of light. Unfortunately, there have have been problems with the inability to function properly.
  • Another hindrance of a worldwide switch to LED lamps or lighting is the technological switch that households will have to make to accommodate to the lights. For the lights to be energy efficient, the fixtures would need to be switched.


[edit] References

  • Light Up the World Foundation (2007) [3]
  • Ningbo G-Nor Electronics Co.,Ltd.(2007) [4]
  • Molecular Expressions: Optical Microscopy Primer, Physics of Light and Color(2005) Available: [5]