Characteristics and Efficiency of Different Light Sources

Power & Energy Services, Residential and Business: APS

By using this Web site,
you accept our Terms of Use
and Privacy Policy agreements.

Characteristics and Efficiency of Different Light Sources

The performance and features of a light source needs to be matched to the lighting task being performed. In order to select the right light source for the job, you should consider important performance variables such as light output (Lumens), efficiency (Lumens/Watt – technically referred to as “efficacy”), lamp life, and color rendering properties measured in terms of the Color Rendering Index (CRI). The CRI is a measure of the degree to which a light source renders colors that are close to true color. For practical purposes it is a number from 0 to 100; the higher the number, the closer to true color. The efficiencies of each type of light source can vary dramatically, so the choice of light source can have a dramatic impact on lighting energy costs. The performance characteristics and efficiencies of common light sources are shown in the table and chart below.

Characteristics of Common Light Sources²

Light Source	Efficiency (Lumens/Watt)	Average Lamp Life (Hours)	Color Rendering Index
Standard Incandescent	5-20	750-1000	100
Tungsten-Halogen	15-25	2000-4000	100
Compact Fluorescent	20-55	10,000	80
Tubular Fluorescent	60-100	15,000-24,000	50-90
Mercury Vapor	25-50	Up to 24,000	15-30
Metal Halide	45-100	10,000-20,000	60-90
High Pressure Sodium	45-110	Up to 24,000	9-70

Cost Comparison of Incandescent and Fluorescent Lamps³

Lamp Type	Energy Costs	First Cost	Maintenance Costs
Incandescent	Much Higher	Lower	Higher
Fluorescent	Much Lower	Higher	Lower

² Lighting Fundamentals Handbook, EPRI, 1992.
³ Energy Star Small Business Guide, U.S. EPA, 1997.