Online Guide to Energy-Efficient Commercial Equipment

Note: The lighting community generally uses the term "lamp" to mean the actual source of light--what the public usually calls the "light bulb."  In this chapter, we use "lamp" to refer to the light source. 

The amount of light radiated by a lamp is measured in lumens.  The lamp's "efficacy" is given as the ratio of lumens per watt of electric input. Generally speaking, higher-efficacy lamps are more energy efficient, but lamps with the greatest efficacies also tend to have the highest wattages. So purchasers and specifiers should choose the most efficacious lamp that is appropriate (in terms of light output, color, and other factors) for a given application.

The most commonly used light sources in commercial applications include:

• Incandescent 
• Fluorescent 
• High-intensity discharge (HID) lamps 
• Other sources

Fluorescent lamps are the most common lamp type in commercial buildings and are by far the largest source of lighting energy use in commercial buildings -- accounting for 56 percent of lighting energy use (77 percent of lamps, 78 percent of lumen output). These are followed by incandescent lamps, which account for 32 percent of lighting energy (22 percent of lamps, 8 percent of lumen output), and HID sources which use 12 percent of lighting energy (2 percent of lamps, 14 percent of lumen output) [U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Technologies Program. 2002. U.S. Lighting Market Characterization, Volume 1: National Lighting Inventory and Energy Consumption Estimate. Prepared by Navigant Consulting. Washington, D.C.: U.S. Department of Energy]. See the table below for a sense of the features that distinguish these lamps.

Comparing Commercial Lamp Types
	Incandescent		Fluorescent		HID
	Standard	Halogen	Full-Size or U-bent	Compact	Metal Halide	High-Pressure Sodium
Wattage	3-1,500	10-1,500	4-215	5-58	32-2,000	35-1,000
Lamp Efficacy (a) (lumens per watt)	6-24	8-35	26-105	28-84	50-110	50-120
Average Rated Life (hours)	750-2,000	2,000-4,000	7,500-24,000	10,000-20,000	6,000-20,000	16,000-24,000
CRI (b)	99	99	49-96	82-86	65-96	21-65
Start-to-Full Brightness	immediate	immediate	0-5 seconds	0-5 minutes	1-15 minutes	4-6 minutes
Restrike Time (c)	immediate	immediate	immediate	immediate	2-20 minutes	1 minute
Lumen Maintenance	very good	excellent	very good	good	fair/good	very good

Notes:
(a) For fluorescent and HID lamps, lamp efficacy includes ballast losses.
(b) CRI (the color rendering index) describes the effect of a light source on the color appearance of an object. The highest CRI attainable is 100. CRI values of 70-85 are typical for modern T-8 and compact fluorescent lamps.
(c) Restrike time is the cool-down period required before a lamp can be restarted once it has been turned off.  The shorter restrike times for metal halide lamps are achieved with pulse-start lamps and ballasts. When considering lighting systems requiring frequent or automatic switching, note warm-up and restrike times. 

Sources: Updated by ACEEE in 1999 from New York State Energy Research and Development Authority. 1991. Commercial Lighting Technology Assessment. Albany, N.Y.: New York State Energy Research and Development Authority; Foley, G. (Alliance to Save Energy). 1997. Personal communication. August.

Incandescent Lamps

The original lamp invented by Edison was an incandescent lamp that generated about 5 lumens per watt. Modern incandescent lamps (including tungsten halogen lamps) are generally rated between 10 and 20 lumens per watt. Relatively recent advances in halogen lamps have resulted in halogen infrared reflecting (HIR) lamps that can achieve 25 to 35 lumens per watt. Within the incandescent reflector product group, there is a range of HIR products now available. In general, however, incandescent and halogen lamps are relatively low efficacy sources and their use should be limited. In contrast, fluorescent, compact fluorescent, and high-intensity discharge (HID) lamps have high efficacies, typically 60 to 100 lumens per watt. As a general rule of thumb, 1 watt of fluorescent or HID lighting equals the light output of 3 to 4 watts of incandescent lighting. This difference is so significant as to make lamp selection the single greatest energy efficiency decision in commercial lighting systems.  Looked at another way, a good incandescent converts roughly 5% of the input energy to light.  

Fluorescent Lamps

Fluorescent lamps range in efficacy from 40 to about 100 lumens per watt, making them generally the most energy-efficient source of electric light for general purpose uses. They are long-lived, offer a range of color quality from fair to excellent, and maintain their light output longer than most other lamps. There are a number of specific fluorescent lamp types in use today:

• Standard full-size and U-bent fluorescent lamps. These lamps are the most widely used light sources for commercial, industrial, and institutional space. They include common 4-foot and 8-foot straight lamps for most commercial lighting as well as other straight lamps and U-shaped lamps. Traditionally, most lamps have been T-12 (i.e., 12/8, or 1.5 inches in diameter).  However, advances in lamp technology are gradually making the T-12 lamps obsolete.  Modern lamps such as T-8s and, most recently, T-5 lamps have many benefits relative to T-12s. Efficacies range from about 80 lumens to as much as 105 lumens per watt for T-8 or T-5 lamps with electronic ballasts.

• Compact fluorescent lamps. These lamps are designed to be used in a variety of architectural and decorative fixtures, as well as task lights, often displacing an incandescent lamp. They can be found in a number of different shapes, including twin tube ("biaxial"), quad tube, triple twin tube ("triple"), flat quad tube, flat 2-D lamp, circline, and twist (looks somewhat like an ice cream cone). Self-ballasted CFLs, consisting of a CFL, a ballast, and a medium screw base, are used primarily to retrofit existing incandescent lamps. Most of these lamps generate between 40 and 70 lumens per watt depending on lamp size and type of ballast.

Modern full-size and U-bent fluorescent lamps, such as T-5s, T-8s, and some T-12s, as well as CFLs offer good to excellent color quality and lamp-to-lamp consistency with a choice of color temperature. These lamps also maintain light output longer than other fluorescent lamps and most others. Many modern fluorescent lamps and CFLs can be dimmed with modern electronic ballasts to achieve additional energy efficiency through daylighting and other power reduction strategies. See the table on fluorescent lamp comparison for performance and cost comparisons of fluorescent lamp types matched with electronic ballasts (similar lamps matched with efficient magnetic ballasts use 15 to 20 percent more energy). There are also a few limitations to fluorescent sources. Fluorescent lamps are not suited for use as spotlights, and most fluorescent lamps do not operate properly in very cold or hot spaces. Otherwise, their qualities and cost-effectiveness are superior to most other lamps. Fluorescent lamps also require a small amount of mercury inside to operate. Because lamp mercury content presents an environmental risk on disposal, a number of lamps have been redesigned to use an extremely small amount of mercury.

High-Intensity Discharge Lamps

High-intensity discharge lamps offer efficacies that range from 50 to 120 lumens per watt. Their greatest advantage is their ability to generate a lot of light in a relatively small envelope, making these lamps suitable as spot lights, industrial lights, and street lights, and in other applications where a compact yet intense light source is needed. Further, HID lamps operate over a wide temperature range and have a long life expectancy. However, there are several drawbacks to HID lamps: they require more time than other lamps to warm up and are not well suited for dimming (although recent advances are addressing these limitations).

HID lamps all operate on the same principle. The discharge lamp produces light from a gas or vapor inside an arc tube that is excited by an electrical current passing through it. All HID lamps require a ballast to operate and an initial start-up time of 1 to 10 minutes to achieve full brightness. When the lamps are turned off, the arc tubes require a cool-down period of as much as 20 minutes before they can be restarted. There are three primary types of HID lamps: mercury vapor, metal halide (MH), and high-pressure sodium (HPS). Of these, mercury vapor lamps are the least efficient and should be avoided.  Additionally, low-pressure sodium lamps, while extremely efficacious (180 lumens per watt), have very poor color rendering; as a result, they are typically used only in applications where color is not important, such as outdoor lighting. 

• Metal halide lamps: These lamps offers the best color while maintaining high efficacy. Lamps between 30 and 150 watts are generally compact and exhibit efficacy between 50 and 80 lumens per watt. Larger lamps of 175 to 2,000 watts can reach over 100 lumens per watt. As a result of recent breakthroughs, ceramic MH lamps achieve color quality nearly as good as fluorescent lamps. Future advances are also expected to make these lamps smaller, warm up faster, and operate more consistently over their life.
• High-pressure sodium lamps: HPS lamps offer extremely long life, consistent performance, and excellent economy. Lamp efficacy ranges from 50 to 120 lumens per watt. They have become the standard for roadway lighting throughout most of the United States. However, their modest color quality (distinctly pink-orange) can affect human visual performance as well as color recognition. So indoor applications have been limited to warehouses and heavy industry. Improved-color HPS lamps have been developed but energy efficiency and other characteristics of these so-called "white" HPS lamps are mediocre and therefore they have limited applications in comparison to MH lamps.

Other Sources

Keep an eye out for emerging lighting technologies, particularly solid state lighting such as light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) for task lighting and (eventually) general illumination. These technologies have been used effectively for signal indication and signage (e.g., LED traffic signals and exit signs) as well as for flat displays (OLEDs). But as the technology improves and the costs come down, these options may present significant energy and operating cost savings for broader, general lighting applications.