Tuesday, October 7, 2014

Light Bulb

A common symbol or icon for an idea is a picture of a light bulb. Thomas Edison, famous for inventing the modern light bulb (among many other useful things including the record player), is the archetype for the American Inventor and even for American innovation.

Now three Japanese scientists have been awarded for their innovation. Isamu Akasaki, Hiroshi Amano and Shuji Nakamura have been given the Nobel Prize for Physics for their invention of the blue LED (light emitting diode). When they produced bright blue light beams from their semi-conductors in the early 1990s, they triggered a fundamental transformation of lighting technology. Red and green diodes had been around for a long time but without blue light, white lamps could not be created. (Color television … even before LED flat screens … used the three primary colors of red, green, and blue to produce the full rainbow (spectrum) of colors.)

Despite considerable efforts, both in the scientific community and in industry, the blue LED had remained a challenge for three decades. These three succeeded where everyone else had failed. Akasaki worked together with Amano at the University of Nagoya, while Nakamura was employed at Nichia Chemicals, a small company in Tokushima.

Their inventions were revolutionary. Although incandescent light bulbs lit the 20th century, the 21st century will be lit by LED lamps. Thanks to their invention, LED lamps can emit a bright white light, are long-lasting, and energy-efficient. They are constantly being improved, getting more efficient with higher luminous flux (measured in lumens) per unit electrical input power (measured in watts). The most recent record is just over 300 lm/W, which can be compared to 16 for regular light bulbs and close to 70 for fluorescent lamps. That works out to around 5% efficiency for incandescents and the much improved, but still very poor 25% efficiency for CFLs.

As about one fourth of world electricity consumption is used for lighting purposes, these LEDs contribute to saving the Earth's resources. Materials consumption is also diminished as LEDs last up to 100,000 hours, compared to 1,000 for incandescent bulbs and 10,000 hours for fluorescent lights.

It appears to me that the current shift from incandescent to compact fluorescent lamps (CFL) (driven by "green" concerns for both the environment and the wallet) is starting to transition to LEDs. Price remains the biggest disincentive, but volume production is bringing the prices of LED lamps down quickly. A trip down the aisle at Home Depot or Lowe's will quickly demonstrate the surge in LED products.

Improved manufacturing techniques and economy of scale is bringing LED prices down further, and the long life of LEDs improves the economics for home users. CFLs were long lasting compared to the often “burnt out” incandescents, but LEDs are much longer lasting than CFLs. In fact, with modern LEDs, storing replacement bulbs in the closet may become as antique as outdoor plumbing and the dial phone.

A significant feature of LEDs is that the light is directional, as opposed to incandescent and CFL bulbs which spread the light more spherically. This is an advantage with recessed lighting or under-cabinet lighting, but it is a disadvantage for table lamps. New LED bulb designs address the directional limitation by using diffuser lenses and reflectors to disperse the light more like an incandescent bulb. LED lamps can also be designed to support dimmers, a problem for CFLs, and there are more options for size and shape; no need for curly-Q glass designs.

The LED lamp holds great promise for increasing the quality of life for over 1.5 billion people around the world who lack access to electricity grids: due to low power requirements it can be powered by cheap local solar power.

Because of the low power requirement for LEDs, using solar panels becomes more practical and less expensive than running an electric line or using a generator for lighting in remote or off-grid areas. We are already experiencing a wave of garden lighting powered by the sun and rechargeable batteries. LED light bulbs are also ideal for use with small portable generators which homeowners use for backup power in emergencies. Even the trusty flashlight is using LED bulbs.

This may lead to other changes in the future and the power distribution systems and wiring in the modern home may change in response to this new lighting appliance. The 115 volt power in the US, which is optimal for incandescent lamps, is much too high for LEDs. Ironically it is too low for CFLs and they contain circuits to jump the voltage.

In a CFL, electrons from a heated filament flow through the bulb and collide with mercury atoms in the tube. As a result of these collisions, photons are released, but they are in the UV wavelength range and thus not useful for illumination. To convert UV to visible light, the inside of the fluorescent tube is coated with a phosphor. As the emitted UV photons hit this phosphor, the coating glows and gives off the visible light of the bulb.

Although this sounds simple, it requires three different voltage levels to get started and to operate. That’s why older fluorescent lights had starters and ballast and other additional circuits to produce the starting current and maintain operation. Modern CFLs contain miniature circuits in the base to provide for starting and operation.

LEDs, on the other hand, operate at the voltage of a semiconductor junction, about 1.5 volts. So the base of an LED lamp must contain circuitry to reduce the 115 volt to a lower value. It is possible, once LED lights become the only bulbs in the home, that low voltage circuits will become as common as today’s 115 volt wall socket juice. As LED lighting is adopted, 12 volt house wiring may become the standard. (Most modern electronics would operate well on 12 volts, although there are a few home appliances that need higher voltage. Perhaps the house or office of the future will have both 12 volt and 115 volt circuits like many travel trailers and motor homes do now.)

When I finished my basement, I put in two 12v circuits to run low voltage LED lighting in my entertainment/family room and the downstairs bathroom. In the future, this will become much more common.

The lower voltage would be safer from electrical shock, short circuits, and fires. In addition, CFLs contain very hazardous materials including mercury, making waste disposal an issue. So the ultimate shift to LEDs will be good for the environment and for society in many ways.

Although the Nobel Prize is usually given for theoretical discoveries, this invention of the blue LED ranks up there with Edison’s equivalent invention in how it will ultimately change the world. I believe the 20th century was enabled by the light bulb. Now the 21st century may see an equal transition due to the LED lamp.

LED lights. Now that’s a BRIGHT idea!

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