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Lighting in Commercial Buildings

Characteristics of Lighting Types

Efficacy
Efficacy is the amount of light produced per unit of energy consumed, expressed in lumens per watt (lm/W). Lamps with a higher efficacy value are more energy efficient.

Average Rated Life
The average rated life of a particular type of lamp is defined by the number of hours when 50 percent of a large sample of that type of lamp has failed.

Color Rendering Index (CRI)
The CRI is a measurement of a light source’s accuracy in rendering different colors when compared to a reference light source. The highest attainable CRI is 100. Lamps with CRIs above 70 are typically used in office and living environments.

Correlated Color Temperature (CCT)
The CCT is an indicator of the “warmth” or “coolness” of the color appearance of the lamp’s light. The CCT is given in the Kelvin (K) temperature scale, and the higher the color temperature, the cooler the appearance of the light. Below 3,200 K, the light has a “warm” appearance and above 4,000 K the light has a “cool” appearance.

Typical Values of Major Lighting Characteristics

Type of Lighting Efficacy
(lumens/W)
Typical Rated Lifetime
(hours)
Color Rendering Index Correlated Color Temperature
(K)
Incandescent 10-19 750-2,500 97 2,500-3,000
Halogen 14-20 2,000-3,500 99 2,800-3,000
Standard Fluorescent        
—T5 25-55 6,000-7,500 52-75 3,000-6,500
—T8 35-87 7,500-20,000 52-90 3,000-6,500
—T12 35-92 7,500-20,000 50-92 3,000-7,500
Compact Fluorescent 40-70 10,000 82 2,700-6,500
High Intensity Discharge (HID)        
—Mercury Vapor 25-50 29,000 15-50 4,000-7,000
—Metal Halide 50-115 3,000-20,000 65-90 3,000-4,400
—High Pressure Sodium 50-124 29,000 22 1,900-2,200

Source: 2008 Buildings Energy Data Book, Table 5.6.9, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (buildingsdatabook.eren.doe.gov); U.S. Lighting Market Characterization, Vol. 1: National Lighting Inventory and Energy Consumption Estimate, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (www1.eere.energy.gov/buildings/ssl/tech_reports.html/lmc_vol1_final.pdf.

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