Sources & Auxiliaries
 
Last Update: November 1, 2011
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Technical Background

This section is intended to provide an overview of the technical background needed to understand and evaluate energy efficient lighting systems.  Key metrics, such as those for evaluating efficiency, color, and life, are introduced and discussed.  An initial introduction and comparison of key light sources is presented in this section, while more detailed information that is specific to particular lighting technologies is presented in the sections that follow.   

Energy Efficiency Terminology
The efficient use of lighting has never been more important than it is today given the environmental and economic concerns that are driving the lighting market.  Figure 6.1.1 illustrates the dominate role that energy usage plays on the overall life cycle cost of a lighting system. 
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Lamp Life
The life of a lamp is typically quoted as a single value, usually in hours. In reality, it is one point on a statistical function. The single value is the number of hours a group of lamps can be expected to operate before 50% have failed.
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Maintenance of Light Output
Plots of light output versus time for lamps, known as lumen maintenance curves, are published by lamp manufacturers. Lumen maintenance curves can vary significantly between different light sources and sometimes even within lamp groups themselves. 
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Color
There are several metrics that relate to color and lighting.  These metrics include chromaticity, which defines how “warm” or “cool” a light appears, and color rendering index (CRI), which attempts to quantify how accurately a light source renders colors. 
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Power Quality 
The power that a lighting system draws, expressed in watts (W) or kilowatts (kW), and the energy the system consumes, expressed in watt-hours (Wh) or kilowatt-hours (kWh), are the primary power-related metrics for evaluating lighting systems. 
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Lamp Temperature Characteristics
Electric lamps generally operate over the range of ambient temperatures they encounter with limited affect on their performance. The major exceptions are fluorescent lamps and LEDs which will be briefly discussed here and reviewed in more detail in their respective sections.  
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Sources & Auxiliaries

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