Education

Announcements

2011-12 IES Roadshow Schedule
Click Here >

The Lighting Handbook, 10th Edition
PDF version >
Print version >

Standard 189.1 Design of High-Performance Green Buildings >

Advanced Energy Design Guides: Free Download >

TM-23-11 - Lighting Control Protocols: Free Download >

Model Lighting Ordinance – 2011:
Free Download >
Undocumented Changes - Memorandum >

2012 LIGHTFAIR International >
May 9-11, 2012 | Las Vegas, NV

LD+A The Magazine of the Illuminating Engineering Society of North America

Lamps & Fixtures in the Field

Don’t Let BUG Drive You Batty

There’s an old saying that “good intentions sometimes produce unintended results.” Consider this example: Concerned about noise pollution, a local airport authority set stricter limits on the allowable sound levels produced from jet engines. As a result, an aircraft manufacturer developed a smaller, quieter version of its jet engine to meet the newly prescribed levels. But because the new engine was also less powerful, the number of engines per plane had to be increased from two to six to power the same aircraft. The new six-engine plane, however, required considerably more fuel and maintenance than the twin-engine version, meaning ticket prices increased. And as it happened, the new plane actually produced more sound than the previous version, causing local residents to be even angrier than they were before the new ordinance was adopted.

The above scenario is the “law of unintended consequences” in action. The lighting industry may also susceptible to this law as a result of the BUG rating system for outdoor luminaires, argue Michael Smolyansky (Cooper Lighting Canada) and Paul Mitchell (Sternberg Lighting). The Backlight, Uplight and Glare (BUG) rating is the new luminaire classification system (LCS) intended to measure the absolute value of obtrusive light emitted by a luminaire, with no relation to the luminaire’s ability to accomplish its main task--which is to provide needed outdoor lighting to a specific area. While BUG is a significantly improved metric for evaluating a single luminaire, when misapplied to develop a site plan, the results can be very similar to the airplane scenario.

The figure below shows two options for lighting a typical parking lot. The layout on the left uses two 30-ft poles with single 400-W luminaires. The layout on the right uses two 30-ft poles with three 150-W luminaires per pole (six luminaires total). Both lighting designs meet the requirements of IES RP-20 for enhanced security light in parking lots. Both meet the Model Lighting Ordinance (MLO, currently under public review) requirements in terms of lumens per site for lighting zone LZ-2. Both also conform to the MLO requirement for total spill light outside the boundary line.

	400w	150w
Luminaires	2	6
Initial lumens per site	84,000	84,000
Illuminance Average	1.1 fc	1.07 fc
Illuminance Minimum	0.6 fc	0.5 fc
Lumens per site	2.83 lm/sf	2.83 lm/sf
Total watts	904	1110
Average Illumination on "box" surrounding the site	0.04 fc	0.05 fc
% of spill light outside boundary line	5.90	7.40;
BUG rating	B5-U3-G5	B3-U2-G2

According to the currently proposed MLO, the only permissible solution for LZ-2 is the use of luminaires with a Glare rating of G2 or less. As the table here indicates, a 150-W luminaire meets this rating, but the 400-W fixture does not. However further anaylsis shows that the 400-W luminaires produce less light spill than the 150-W luminaires. In addition, the design utilizing 400-W luminaires would have a lower carbon footprint based on the conservation of energy and resources.

Utilizing only 150-W luminaires, with the currently mandated G rating of 2 or less, in lieu of using 400-W luminaires with a G rating of 5, produces the following negative results:

Total light trespass increases from 5.9 to 7.4 percent.
Energy consumption increases 19 percent.
The carbon footprint from the manufacture and operation of six fixtures instead of two is substantially increased.

The adage “the right tool for the right job” applies to this scenario. Indeed, BUG is an effective tool for comparing individual luminaires of similar lumen output, but it should not be utilized as either a metric or limiting factor in the design of a site plan.

July 2011