Fixing the Fixtures

Michael Siminovitch is a staff scientist with the Lighting Systems Research Group and Evan Mills is assistant director of the Center for Building Science, both at Lawrence Berkeley Laboratory, in Berkeley, California.

With U.S. sales approaching 50 million lamps per year (and 250 million globally), compact fluorescent systems are increasingly popular. However, efforts to promote their use in the residential market have mostly been limited to utility rebate programs for screw-based lamps. Concerns about performance and economics suggest that integral screw-based (as opposed to modular pin-based) technologies are, at best, a short-term approach to the ultimate, widespread residential application of the CFL.

The fundamental reason that screw-based CFLs are only a temporary solution is the so-called snapback effect: When these units burn out--or perhaps even sooner--they can easily be replaced with the inexpensive and inefficient incandescent lamp, eroding the conservation potential. This occurs in part because consumers generally will not keep $10-$15 screw-based CFLs in their home inventory, and because of the likelihood of unacceptable performance for this type of a CFL strategy.

The push for affordability has led to the availability of some inexpensive screw-based CFL products that have marginal quality, leading to premature failures and consumer dissatisfaction. Some CFLs are now being made smaller so that they fit into more existing home fixtures (see Downsizing the CFL, HE Jan/Feb '94, p. 5). But reducing dimensional characteristics can result in constricted ballast compartments, compromising quality and operation of the electronic components.

Part of the problem stems from the fact that most existing home fixtures are designed for the incandescent A-lamp, which has a very different luminous distribution than the more linear and non-symmetrical CFL. Replacing an incandescent A-lamp with a CFL noticeably changes the optical distribution of the overall fixture, sometimes reducing perceived brightness. Efficiency should be assessed using the total lumen output and light distribution of the fixture system where the lamp is installed, not just the output of the screw-based assembly by itself.

Since consumers are interested in the total light output and the quality of the illumination, component efficiency (for instance lamp efficacy, measured in lumens per watt) is not as important as actual system performance characteristics--how well a lamp system works when inserted into a fixture. When retrofit into existing fixtures, some CFLs perform dramatically differently from others.

Pin-based lamps in dedicated fixtures, on the other hand, allow for easy re-lamping with maximum lifetime energy savings and economic benefits. Dedicated fixtures can be designed to optimize the optical performance and appearance of the CFL.

Taking Advantage of Technology

Screw-based retrofit systems typically combine a lamp, a ballast and a familiar threaded Edison base for quick-and-dirty connection with existing incandescent sockets inside fixtures. The lamp may be integral with the ballast or removable for re-lamping (see Figure 1).

Dedicated systems include a fixture whose elements (electrical connections, ballasting, and optical control) are integrated. A separate, replaceable pin-based lamp can be positioned appropriately to maximize optical distribution and maintain an optimum thermal environment (lamp overheating can result in up to a 25% reduction in light output). As in a commercial fixture, the pin-based lamp plugs into a socket within the fixture.

Fixture geometry can be designed to maximize the optical distribution of the unique compact fluorescent shape, thereby maintaining high fixture efficiency. When the lamps burn out, the fixture can be re-lamped only with a pin-based CFL, for continued savings. A pin-based compact fluorescent lamp is much cheaper than the more complicated screw-based system, so consumers are more likely to stockpile a few. Another benefit is that less solid waste is produced upon disposal, and mercury recovery is less expensive (approximately 50cents for the bulb alone, versus $1 for an integrated lamp).

Other advantages of pin-based systems include greater ability to address power quality issues in the ballast, and easier implementation of dimmable ballasts.

Moving the Market

The only way to ensure that CFL technology's conservation potential is realized is to replace both the incandescent lamp and socket with a dedicated fixture system. Looking at the history of lighting reveals several successful examples of this approach; one is the lighting of commercial interiors. Consider the way pin-based long fluorescent lamps displaced incandescents in the commercial sector in the 1940s, and pin-based halogen lamps swept into popularity in homes in the 1980s.

Until the 1940s, nearly all offices were illuminated with incandescent downlights. With the emergence of the long fluorescent lamp, dedicated pin-based fixtures were produced, and now almost all commercial interiors use linear fluorescent illumination.

We are now seeing a significant movement towards dedicated fixtures for commercial applications of the compact fluorescent lamp. The recessed downlight designed for compact fluorescent lamps is one of the fastest-growing fixture markets in the United States, growing at 5% per year (about twice as fast as floor space).

The dramatic market success of pin-based halogen lighting in the residential sector shows that consumers will accept new lighting approaches and hardware given a clear advance in technology or lighting quality. The key to this success was the design and marketing of the new generation of halogen fixtures. Compact fluorescents, too, can offer some distinct advantages when coupled with well-designed fixtures.

One of the best residential applications for CFLs is outdoors, because of the extended hours of operation. Currently, there are a variety of pin-based CFL outdoor fixtures on the market. These systems, designed specifically for operation of the CFL, are an excellent example of new fixture technology leading to success in the residential sector. Other dedicated fixtures for compact fluorescent lamps on the market include CFL table lamps, surface-mounted fixtures for kitchens and hallways, sconces for wall applications, and recessed downlights. As with any new industry or product, manufacturers depend on increased demand and acceptance of their wares in order to justify manufacture.

Editor's Note: The authors are supporting efforts by the U.S. Department of Energy and Environmental Protection Agency on accelerating the use of dedicated CFL systems in the home. Individuals interested in participating in this project are invited to contact the authors.

• Optimize Thermal and Optical Performance - allows for conductive and convective ventilation strategies, and CFL-specific reflector design

• Aesthetic Integration - easier to design fixtures to minimize glare and be more visually appealing

• Specific Candlepower Distribution - the pattern of light distribution can be precisely determined

• Economic Home Inventory - replacement lamps (without ballast) are less expensive and smaller than integral lamps

• Power Quality and Dimming - availability of extra ballast space within fixture allows for additional components for dimming or controlling power factor and harmonic distortion

• Fixtures Cannot Be Relamped with Incandescent Lamps - the built-in ballast and pin-based socket requires that replacement lamps be CFLs; incandescent lamps won't fit

   

A frequent criticism of CFLs--they don't give enough light--can be traced partly to overheating, either due to the CFLs being used in fixtures designed for incandescent lamps, or simply because they are installed base down. Lamp temperature depends on several factors: lamp and fixture geometry, lamp wattage, ballasting, ambient temperature, lamp orientation, and air circulation.

A compact fluorescent lamp operates most efficiently at a specific mercury vapor pressure. High temperatures can cause more of the liquid mercury to vaporize, lowering the lumen output of the lamp below what it would be under design conditions. Enclosed fixtures that allow heat to build up around the lamp can thus lower the efficicacy of the lamp.

Lamp positioning also affects the vaporization of mercury. The mercury inside a compact fluorescent lamp condenses at the coldest point on the lamp. When the lamp is in base-down position, the mercury drips down near the ballast, where it revaporizes because of the higher temperatures generated by the lamp electrodes and ballast. As a result, some CFLs operating in a base-down position produce 15% to 20% less light than when installed base up. Circlines and CFLs with coiled tubes or other shapes that allow the mercury to collect away from the ballast are not as affected by position.

Several adjustments can be made to both the lamps and the fixtures to alleviate thermal efficiency problems. Lamp adjustments include fitting a small copper strip within the bottom of the lamp to conduct heat away. Dedicated CFL fixtures can be designed to minimize temperature by adding ventilation slots and adjusting the lamp's position. Many manufacturers make vented fixtures for recessed CFL downlights that are designed to tilt the lamp downward by 5 to 10 degrees so that the mercury collects at the cooler tip of the lamp. This lamp design, developed at Lawrence Berkeley Laboratory, increases light ouput by up to 20% and adds little or nothing to the production cost of the fixture.

Figure 1. Base location affects performance in a compact fluorescent lamp.

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