Lighting accounts for about 20 percent of total energy use in commercial buildings, making it a primary target in cost-saving upgrades. A number of factors can affect lighting choices, including the type of building, occupant traffic, and occupancy schedules. Understanding how different lighting technologies work, and how they compare, will help you select the right lighting for your application.
The linear fluorescent lights commonly used in offices and other commercial and industrial facilities come in T12, T8, and T5 varieties. The T stands for tubular while the number refers to the diameter of the lamp in eighths of an inch. For example, a T8 lamp has a diameter of 1 inch or 8/8 of an inch. T12 and T8 lamps can attach to the same fixture, while T5 models are slightly shorter. T8 and T5 lamps are more efficient because they are smaller in diameter and use electronic ballasts. Although standard T8 and T5 lamps have less light output than T12s, high-performance models are also available.
Due to federal energy-efficiency regulations, T12 lamps are no longer manufactured or imported for sale in the United States. Contact your lighting supplier for replacement options.
High-intensity discharge lamps
High-intensity discharge (HID) lamps are typically used for outdoor lighting or high-ceiling indoor applications. They generally require a warm-up time of several minutes and a cool-down time before restriking. Commonly used HID lamps include metal halide and high-pressure sodium.
- Metal halide lamps include both metal halide (rare earth metal salts) and mercury gases. The addition of metal halide gases improves efficacy and color quality.
- High-pressure sodium (HPS) lamps use sodium as the main light-emitting element, along with a small amount of mercury. They generally have a yellow tint but can produce a warm, white light. They are widely used because of their long lifespan and high efficacy.
Light-emitting diodes (LEDs) are highly energy efficient and have a long rated life—up to 50,000 hours or more. Made from solid materials, they are very durable and resistant to vibration. LEDs are dimmable, and can start instantly, making them applicable with lighting controls and daylighting strategies.
As a new technology, LEDs typically cost more than conventional light sources and product standards and testing are still in development. The performance of LED products can vary widely.
Comparing lighting technologies
Lighting technologies have different operating characteristics and some are only suitable for certain applications. However, a direct comparison of their performance can still be helpful. The following table provides an overview of the efficacy, color quality, and estimated operating life span of each lighting type. Efficacy is measured in lumens per watt. Color quality is quantified on a scale of 1 to 100 as color rendering index (CRI) where 100 CRI is equivalent to sunlight.
|Lighting Technology Comparison
|| Efficacy (lumens per watt)
|| Life span (hours)
Fluorescent lights are energy efficient and have a long life span, but a relatively poor color quality. HPS lamps compare favorably to metal halides in efficacy and have a longer operating life, but they have a very poor color rendition. LED lights combine efficiency, long life span, and good color quality. As technology advances, the use of LEDs in a variety of applications should continue to grow.
Develop a lighting strategy
A successful lighting upgrade includes careful design, energy-saving controls, and a preventive maintenance program that includes group relamping and proper disposal.
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