Characteristics of Lighting Types
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
|Typical Rated Lifetime
|Color Rendering Index||Correlated Color Temperature
|High Intensity Discharge (HID)|
|—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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