APPLICATION NOTE An In-Depth Examination of an Energy Summary Efficiency Technology Fluorescent lighting is the preferred system for general lighting in many commercial applications. Many types of ballasts, lamps, and fixtures are avail- Efficient Lighting able for energy-efficient, cost-effective, high-quality installations. This Applica- tion Note reviews these components, Using Full-Size including their operating characteristics Fluorescent Lamps and application. Full-sized fluorescent systems (those and Fixtures with lamps an inch or more in diameter) can be optimized in a number of ways. Simply removing lamps in overlit areas often yields large energy savings and rapid paybacks. The right lamp-ballast combination can improve efficiency sig- nificantly. For example, nearly any facil- ity using magnetic ballasts and T12 lamps can be retrofitted with electronic ballasts and T8 lamps for energy sav- Summary .............................................1 ings. Improving fixtures so that light is distributed efficiently can also reduce How This Technology Saves energy use as well as improve visual Energy .................................................2 comfort. Types of Energy-Efficiency Measures .............................................3 Energy savings of 50 to 80 percent are possible with retrofits of old fluorescent Applicability ........................................8 systems. Designs for new construction can also be significantly more efficient Field Observations to Assess than conventional practice. Continued Feasibility............................................9 energy savings can be assured by proper maintenance, including a pro- Estimation of Energy Savings .........11 gram of inventory control, and a well- Cost and Service Life .......................11 designed operation and maintenance program that includes relamping and Laws, Codes, and Regulations........13 cleaning schedules. Definitions of Key Terms .................14 References to More Information......15 Major Manufacturers ........................15 Copyright © May 1997, Pacific Gas and Electric Company, all rights reserved. Revised 4/25/97 visible photons, or “fluoresce.” About 22 How This Technology percent of the energy used by the lamp Saves Energy is converted to light. Altering the phos- phors produces different qualities of white light. A fluorescent lighting system (Figure 1) consists of a line voltage and/or low- While several mechanisms exist to voltage controls to switch the lights 1 strike the arc, all fluorescent lamps use on/off or dim them; a ballast , which is a a power conditioning device called a power regulator; a lamp which gener- 20a Lighting Circuit (480/277v or 208/120v) Light Fixture Line Voltage Ballast Switching Breaker Panel Lamps Other Other Switched Lights on Other Zones Switch Lighting Circuits Low Voltage Controls (Timers, Occupancy, Dimming, etc.) Figure 2: Schematic of Fluorescent Lighting System (Source: E Source) ates light; and a fixture that houses the ballast which amplifies line voltage to lamp and determines distribution of the start the lamp, and limits current to light. A luminaire is a complete lighting maintain its arc. Ballasts also ensure unit including lamp(s), ballasts, reflec- control and safety in a variety of failure tors, and shielding and diffusion com- modes. For optimum performance, a ponents. particular ballast must match a specific lamp’s current requirements. The basic fluorescent lamp contains low-pressure mercury vapor and inert Visible Photon gases in a partially evacuated glass tube (Figure 2) lined with specially for- UV Photon mulated compounds called phosphors. - + - + - The action of an electric arc in this at- - Hg + mosphere causes the phosphors to emit - + 1 Bold italicized words are defined in the section Figure 1: Fluorescent Lamp titled “Definition of Key Terms” Operation (Source: E Source) PG&E Energy Efficiency Information© “Full-Size Fluorescents” Page 2 Three different methods can start fluo- lamps in the fixture. The fixture may be rescent discharge in lamps. With a few below the ceiling, lighting ceiling and exceptions, the starting method of the walls as well as floor. There may be a lamp and the ballast must match. metallized reflector in the fixture to more (Mismatches either do not start, or burn efficiently distribute the light from the out the lamp, the ballast, or both.) Pre- lamps. Instead of T12s, lamps will be heat starting is an older method that skinnier “T8” units, only one inch in di- causes flickering for several seconds ameter. The ballast will use electronic before the lamps ignites. Rapid starting switching to regulate power to the is the most common method; lamps lamps, operating at high frequency come on within a second with only a (greater than 20,000 cycles per sec- brief flicker. Instant starting jolts the ond). Compared to T12/magnetic tech- lamp with a high-voltage (400 to 1,000 nology, T8 lamps and electronic ballasts V) pulse that starts it in under a tenth of have better lumen maintenance, an op- a second. timal operating temperature that matches conditions in fixtures more Baseline Fluorescent Lighting closely, and higher intrinsic efficiency System because of the greater frequency of ex- citation in the arc. The typical or “baseline” system in commercial facilities uses 4-foot lamps in a 2’ by 4’ fixture installed in the grid of Types of Energy- a suspended ceiling. The lamps are one Efficiency Measures and one-half inches in diameter, com- monly called “F40/T12,” where “40” in- dicates nominal power consumption in Fluorescent lighting can be optimized in watts and “12” denotes diameter in several ways: correcting overlit situa- eighths of an inch. The ballast uses tions by delamping, using the highest magnetic transformers operating at line efficacy lamp-ballast systems, and ap- frequency (60 cycles per second). Al- plying appropriate control strategies. though there are more efficient types, Each of these measures is discussed today’s magnetic ballasts are some- below. times called “energy-efficient magnetic ballasts” because they are slightly im- Savings from Reducing Over- proved from those manufactured before lighting the early 1980s. Many spaces simply have too much Energy-Efficient Fluorescent electric lighting, and substantial energy Lighting System can be saved by reducing total light output. This can be done by removing An energy-efficient fluorescent system lamps, converting 3- or 4-lamp fixtures look much like the baseline, but its to 1-, 2-, or 3-lamp fixtures, retrofitting components and configuration signifi- with lower output lamp-ballast systems, cantly reduce energy consumption. If or using dimming or other control sys- overlighting existed, there may be fewer tems. Such retrofits typically provide PG&E Energy Efficiency Information© “Full-Size Fluorescents” Page 3 large energy savings and rapid pay- levels, with minimal energy savings and backs. Reducing light output should be a payback of nearly 5 years. done with attention to the quality of the resulting light, its distribution, surface Improving Fixture Efficiency brightness, and glare potential. Distributing light efficiently is as impor- Illuminance is measured in footcan- tant as generating it efficiently, and can dles, using an illuminance meter. The dramatically affect visual comfort. Illuminating Engineering Society of North America recommends typical av- Fixture efficiency refers to how well the erage illuminance levels in its Lighting unit gets the light from the lamps out of Handbook, 8th edition. If measurements the fixture. The main components of a in a space show that average levels are typical fluorescent direct downlight fix- significantly higher than these, the ture are the housing, a lens or louver space is a candidate for some kind of system, and possibly a reflector. See light output reduction. Figure 3. Reducing overlighting saves energy and Reflector Retrofits reduces the cost of lamp and ballast re- placement. There are no disadvantages Reflectors are specially shaped retro- as long as the distribution of light is not fittable metal sheets that improve (or compromised. attempt to improve) the efficiency of and distribution of light from conventional Case Study: Light Levels Affect ceiling-mounted fluorescent downlight Efficiency Opportunities at fixtures. They can significantly decrease University Facilities the internal losses of fixtures and widen or narrow their light distribution, often At a large university, foot-candle meas- allowing significant energy savings from urements showed some spaces overlit delamping. and some underlit. In one building, classroom light levels exceeded 75 footcandles, and one-third of the lamps Fixture Housing were removed to reduce light to the de- sign level of 60 footcandles. With a Reflector switch to electronically ballasted T8 lamps, this resulted in energy savings of over 50 percent with a payback of under two years. Parabolic Louver In the nearby library, however, half the ceiling-mounted fluorescent fixtures had Figure 3: Typical Fluorescent been disconnected years ago as an Downlight Fixture (Source: Metal Optics) “energy savings” measure and light lev- els were below recommendations. A ret- rofit with electronically ballasted T8 lamps increased light output to design PG&E Energy Efficiency Information© “Full-Size Fluorescents” Page 4 Reflectors are available from over two goal to achieve, and is less a function of dozen manufacturers. Innovative de- how good the reflector is than how bad signs, mounting