Luminaire Ratings On The US Agenda
Luminaire Ratings On The US Agenda
Standards are one method that governments use to effect a change in the way energy is utilized. Even if standards are voluntary, they can still significantly impact the product line of manufacturers whose equipment fails to meet the standards. "Luminaire efficacy ratings", and voluntary standards based on those ratings, are currently under consideration in the US.
Mention the subject of efficiency standards to a group of US luminaire manufacturers and you'll find yourself as popular as a teetotaler at a Bacchanalia. But as part of the 1992 Energy Policy Act (See IAEEL Newsletter 1/93) voluntary fixture efficiency standards are-together with luminaire testing procedures and product labeling-being considered by the US Federal Government as one way to reduce the energy consumption of building lighting systems. A few states already incorporate fixture efficiency standards in their building codes.
A fixture efficiency standard would specify minimum fixture efficiency values for various classes of commonly used luminaires. By carefully setting minimum performance values, standards would help "weed out" inefficient fixtures within each product class (lensed troffers, wraparound lensed, and parabolic-louvered fixtures are examples of fluorescent fixture product classes) and manufacturers would be encouraged to produce fixtures that are more efficient. (Fixture efficiency (FE) is the ratio of the lumens emitted by the fixture divided by the total lamp lumens). Most modern fluorescent downlight fixtures have fixture efficiencies between 65% and 70%. But some fixtures (for example fluorescent downlight fixtures with small-cell parabolic louvers) have efficiencies well under 50%.
Critics argue that fixture efficiency standards are inherently flawed because they address only one component of the whole lighting system-the fixture-while ignoring that a luminaire is in fact a system, consisting of lamps and ballasts as well as the fixture. In an effort to address this criticism, the National Electrical Manufacturers Association (NEMA) has floated the concept of a standard based on a luminaire efficacy rating (LER). LER is a figure of merit that can be used to unambiguously rate luminaires according to their efficacy-the luminaire's light output divided by the luminaire's input power. LER is defined as follows:
| . | . | Total rated lamp lumens x Ballast factor x Fixture efficiency |
| LER | = | ____________________________________ |
| . | . | Luminaire input watts |
Note that the fixture efficiency is one term in the LER. But LER also includes the ballast factor (which expresses the actual lumens delivered by a lamp/ballast system relative to the lamp lumen ratings as published in the lamp catalogs) and luminaire input watts (as provided in a standard photometric test). That is, LER considers the efficacy of the lamp/ballast system in addition to the fixture efficiency.
LER has several potential advantages over a simple fixture efficiency standard.
First, LER has units of lumens per watt; thus it explicitly addresses the question of luminaire efficacy.
Second, LER lends itself to labeling. Manufacturers could easily label their luminaires according to LER in a similar manner as refrigerators and all other major household appliances are now labeled.
Third, since the LER approach is system-based rather than component-based, it would be easier for manufacturers to comply with a luminaire efficacy standard than a standard based strictly on fixture efficiency.
For example, a luminaire that would not otherwise meet the minimum LER for that product class using standard energy-efficient ballasts and lamps, would comply if it was equipped with a more efficient ballast (such as an electronic ballast). The manufacturer could demonstrate through testing that the luminaire complied using the advanced ballast.
Perhaps the most intriguing aspect of LER is its simplicity- it is simply the ratio of how much light we get from a fixture divided by the amount of power we must supply to get that light. LER gets to the core of what energy efficiency is all about -to get more energy service using less energy.
A successful LER standard must address the question of luminaire classification. Different LERs should be required for different luminaire classes since a high-end luminaire intended for computer tasks, for example, should be allowed a lower LER than a lensed troffer. NEMA has circulated a luminaire classification scheme which, in this writer's opinion, is too complex for effective standards. Nonetheless, it should serve as a point of departure for the development of a simpler classification scheme.
Luminaire efficacy standards will never be popular with luminaire manufacturers whose products will be affected. But a properly-framed LER standard may be more attractive than a simple fixture efficiency standard while still providing federal policymakers with a tool to increase the efficiency of the nation's lighting systems.
Francis Rubinstein
Technical Editor, IAEEL Newsletter
The author is leading the Lighting Systems Research Group at Lawrence Berkeley Laboratory, California, USA.
Address:
LBL, MS 46-125, CA 94720, USA
Fax: +1 510 486 6940
E-mail: FMRubinstein@lbl.gov