The United States Energy Information Administration (EIA) estimates that lighting in the United States represents about 25 percent of our total energy usage. As a result, considerable effort is underway in academia and industry to develop more efficient light sources to replace incandescent bulbs that are only 10 percent efficient in converting electrical current into light.
The first lighting improvement in over one-hundred years is the curly-cue shaped compact fluorescent lamp (CFL) that is three times more efficient than the incandescent lamp. Still, most of its output energy is lost as heat.
The invention of the blue light-emitting-diode (LED) is three times more efficient than the CFL but has serious color problems. Its color is often referred to as ghostly, flat, cold, harsh and unpleasant. A banana looks forever green under its glow. The addition of a phosphor coating to simulate white light decreases the otherwise improved efficiency.
However, there could be a revolution in lighting if the highly efficient LED light could be softened - without a loss in efficiency - to more closely match the warmer and richer color of the low cost incandescent bulb. The incandescent bulb partially emulates the natural white color of the Sun.
That is exactly what Lexington-based QD Vision, Inc., a spinoff of MIT, has accomplished using nanotechnology. The product name is Quantum LightTM Optic and the lamp is termed a quantum LED (QLED). This product is used by LED lighting manufacturers to produce both lamps and downlighting fixtures that emulate the warm colors of an incandescent bulb but provide much greater light power and lamp life-time.
QD Vision estimates that the “full conversion of existing down-lights and track heads in the United States represents an annual savings of more than 35 billion kW hours of electricity (nearly $4 billion at U.S average pricing), which is the equivalent of nearly 6 power plants or more than 60 million barrels of oil per year."
The mechanism behind this extraordinary development is the redistribution of color by means of “quantum dots”. Quantum dots are microscopic (less than 100 nanometer in diameter) semiconductor elements that possess unusual properties when compared to the properties of the same material when it is large enough (macroscopic) to be seen with the naked eye. At least 100 million quantum dots would be needed to cover the flat-head of a typical sewing-pin.
To understand how quantum dots work requires a brief discussion of what happens to a semiconductor when it becomes the size of a quantum dot. A typical semiconductor material like gallium arsenide (GaAs), used to manufacture red-colored light-emitting diodes, when reduced to a quantum dot begins to display optical properties that are more like a molecule than those associated with a macroscopic sample. The emitted colors of the dot when excited by blue light become constrained by the dimensions of its structure. In particular, the emitted colors can be tuned through size reduction to emit more energetic colors than red - such as orange, yellow and green.
The ability to tune the color of a quantum dot offers a way to redistribute the harsh LED light by placing a specially designed layer of quantum dots in front of the LED lamp thereby effectively transforming a portion of the overly abundant LED blue light into a warmer red light. The overall effect of the quantum dots is to produce illumination that is much closer to natural light.
This ability to redistribute color using a quantum dot is extraordinary. The fact that the conversion efficiency from turning blue light into red, or orange, or yellow is almost one-hundred percent was the final breakthrough. The light power of the LED is retained, only its color is changed. QD Vision uses this mechanism to manufacture a quantum dot thin-film-plate optic that is placed over the LED (refer to photo).
The QDVision Optic uses photoluminescence to achieve QLED performance. Photoluminescence occurs when incident light excites the quantum dot to emit. However, quantum dots can also be excited electrically (electroluminescence) and this characteristic opens up another realm of marketing possibilities. In fact, the company was recently awarded a 1.38 million dollar contract by the U. S. Department of Defense to develop specialized devices based on electroluminescent quantum dots.
QD Vision’s achievement in quantum dot nanotechnology has led to the creation of a more natural light that requires less power. In addition, the color of the light is precisely tunable. The quantum dots are also reliable and stable and manufactured at a competitive price. This breakthrough has opened the door to new possibilities in energy conservation.
The QD Vision Optic has arrived. The revolution in lighting has begun.