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It's Not Easy Being Green

Jul 1, 2008 12:00 PM, By Carla Gallina, Lighting Designer

Environmental impact

In addition to lighting and energy performance, environmental emissions and toxic waste disposal are of primary importance when considering sustainable lamp choices. All discharge lamps, including fluorescent and M-H, contain mercury. Not all discharge lamps are disposed of in accordance with national and local hazardous waste disposal laws. Incandescent/halogen lamps do not contain mercury; therefore, they have no potential of contributing to the toxic waste stream.

Power plants emit CO₂ and airborne mercury during the production of energy from fossil fuels, such as coal. The debate over the contained mercury of a CFL versus the airborne mercury emissions from the energy production required to operate incandescent and CFL lamps loses impact if the incandescent/halogen lamp requires less energy to operate than the CFL. It's an even more difficult argument if the halogen source consumes less energy and provides more usable light to the space, as is the case when comparing the 37W MR16IR lamp to a 42W CFL when installed in a commercial downlight.

In addition to the amount of energy required to simply produce light, each lamp contains embodied energy, which is the energy required to manufacture, package, transport, and dispose of the lamp and its base materials (i.e., glass, metals, plastics, electronics, rare earth phosphors, and mercury). Assume for a moment that it takes the same amount of energy to produce the MR16/IR as it does to produce a CFL or M-H lamp. It's appropriate to conclude that the embodied energy of the MR16/IR is twice that of the CFL or M-H lamp because its rated life of 5,000 hours is about half of that either discharge source. The net result is twice as many MR16 lamp changes over time. Incandescent system design has the advantage of strategies to increase lamp life and consequently reduce the embodied energy of the lamp due to maintenance. Current energy codes require overall building control systems and local dimming controls. If the MR16/IR is trimmed to 90% via a lighting control system, it will operate for approximately 20,000 hours, which exceeds either the CFL or M-H lamp documented in this report. Upon further observation, there is little or no embodied energy involved with halogen lamp disposal. Because they do not contain mercury, they do not require special packaging, transportation, or recycling at end-of-life.

Getting down to business

Downlights are typical to both commercial and retail design. In application, fluorescent downlights are often used for general illumination because they provide a soft-edged uniformity with height to distance ratios between 1-to-1.0 and 1-to-1.3, and the lamp plus ballast efficacy is relatively high. Unfortunately, commercial fluorescent downlights are extremely inefficient (Table 2). Every lighting professional should question whether soft-edged uniformity is a necessary design requirement. If the answer is yes, then is a fluorescent downlight the most appropriate and sustainable design solution, or should an alternative method for general illumination be considered?

Downlights designed for use with reflector lamps operate at much higher efficiencies, typically around 85%. Basically, the reflector lamp does all of the work of the internal luminaire reflector, and it is positioned within the downlight housing such that little light is lost. The difference in light distribution and spacing distances varies by lamp selection and should be carefully evaluated for each design. If the space does not require absolute soft-edged uniformity, and if a downlight is indeed the right design solution for the space, then a reflector lamp may be a better choice than a non-reflector lamp, such as a CFL.

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© 2012 Penton Business Media, Inc.

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