Volume 7 Issue 3
May 2003    
beam angle - The angle at which luminous intensity is 50 percent of the maximum intensity. bin - To sort or classify light sources (such as light emitting diodes) into groups according to their luminous intensity or color appearance. conduction - The process of removing heat from an object via physical contact with other objects or materials, usually metals. convection - The process of removing heat from an object through the surrounding air. cosine distribution - A property of a light source such that its luminous intensity in a particular direction is proportional to the cosine of the angle from the normal to the source. driver - For light emitting diodes, a device that regulates the voltage and current powering the source. heat sinking - Adding a material, usually metal, adjacent to an object in order to cool it through conduction. illumination - The process of using light to see objects at a particular location. indication - The process of using a light source as something to be seen as in signaling. junction temperature - For light emitting diodes, the temperature of the light-emitting portion of the device (see PN junction), which is inversely correlated with its light output. lumen maintenance - The lumens produced by a light source at any given time during its operating life as a percentage of its lumens at the beginning of life. monochromatic - For light, consisting of a single wavelength and having a very saturated color. PN junction - For light emitting diodes, the portion of the device where positive and negative charges combine to produce light. pulse-width modulation - Operating a light source by very rapidly (faster than can be detected visually) switching it on and off to achieve intermediate values of average light output; the frequency and the duty cycle (percentage of time the source is switched on) are important parameters in the modulation. semiconductor - A material whose electrical conductivity is between that of a conductor and an insulator; the conductivity of most semiconductors is temperature dependent. spectral power distribution (SPD) - A representation of the radiant power emitted by a light source as a function of wavelength. substrate - For light emitting diodes, the material on which the devices are constructed. tri-phosphor - A mixture of three phosphors to convert ultraviolet radiation to visible light in fluorescent lamps; each of the phosphors emits light that is blue, green or red in appearance with the combination producing white light.

Sponsors

California Energy Commission
Iowa Energy Center
Lighting Research Center
New York State Energy Research and Development Authority
Northwest Energy Efficiency Alliance
U.S. Department of Energy
U.S. Environmental Protection Agency
Wisconsin Focus on Energy

Credits

Lighting Answers: Light Emitting Diode Lighting Systems
Volume 7, Issue 3                      May 2003
Authors: John D. Bullough
Program Director: Conan O'Rourke
Editor: Dennis Guyon
Designer/Graphics Developer: James Gross
Julie Bailey
Jonas Concepcion
Technical Developers: Rick Hadley
Joann Coffey
Robert Wolsey


Acknowledgements

NLPIP thanks Stephen Johnson of the Lawrence Berkeley National Laboratory and N. Narendran and Andrew Bierman of the Lighting Research Center for providing technical review of this publication. Other Lighting Research Center personnel who provided technical contributions include Julia Ceriotti, Lei Deng, Russ Leslie, Lenda Lyman, and Ramesh Raghavan.
© 2003 Rensselaer Polytechnic Institute. All rights reserved.

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