Hot Lighting Technology Hits Offices

While it is by no means a new development that almost all office workers have a personal computer on their desk, the installation of quality lighting that minimizes glare on computer screens is. In the recent past, recessed T8 parabolic troffers with semi-specular louvers were widely used to combat glare, but these fixtures can still cause glare because the bare lamps are exposed to the human eye.

08/01/2002


While it is by no means a new development that almost all office workers have a personal computer on their desk, the installation of quality lighting that minimizes glare on computer screens is. In the recent past, recessed T8 parabolic troffers with semi-specular louvers were widely used to combat glare, but these fixtures can still cause glare because the bare lamps are exposed to the human eye.

But the offerings for office lighting have matured a bit over the last few years, shifting to low profile, indirect fixtures with T5 high-output (HO) lamps. By lighting the ceiling and the walls with these lamps, glare can be significantly reduced.

Although indirect T8 fixtures have been available for quite some time, they have often been perceived as being more expensive to install than recessed troffers. As of late, the newer designs and installation features of suspended fixtures have made them more affordable, but by using indirect type fixtures with T5-HO lamps even fewer fixtures can be used, due to the improved fixture optics. Specifically, T5-HO fixtures can typically be spaced at 12- to 15-ft. centers whereas T8 fixtures are typically spaced at eight- to 10-ft. centers.

Thus, by using T5-HO lamps instead of T8, the total number of lamps can almost be cut in half. In addition, a wider range of light levels is possible with T5-HO that have dimming ballasts, and dimmable systems offer more opportunities for using daylight harvesting.

Also, with an eye on energy conservation there has been an increased use of occupancy sensors in private offices. In such applications, shorter lamp life due to frequent switching should not be a concern when T5-HO lamps are installed. Up to 100,000 starts are possible with T5-HO lamps, while T8 lamps on instant-start or rapid-start ballasts only provide up to 17,000 starts.

Office applications

Many companies, especially those with a high-tech profile, have already made the jump to T5-HO. Two such examples are a retrofit project at the Compaq Computer Corp. and a brand new Xilinx, Inc., facility.

Compaq's global services headquarters in Littleton, Mass., includes two buildings with a total of six stories of office space. Before the lighting retrofit, the facilities used 2-ft. by 4-ft. troffers with three-lamp, 34-watt lamps and ballasts. These have been replaced with V-shaped, indirect, single-lamp T5-HO fixtures.

The fixtures, installed in continuous rows on 12-ft. centers and suspended 24 in. from the ceiling, provide uniform illuminance of 30 to 35 footcandles at each desk. Aisles and corridors are defined by 4-ft. fixtures, while perimeter circulation aisles at windows take advantage of natural light. When required, 26-watt compact-fluorescent downlights illuminate vertical surfaces to provide added depth to the space. In conference rooms, single and double rows of two-lamp T5-HO fixtures provide uniform horizontal and required vertical illumination.

"Using these state-of-the-art T5-HO fluorescent systems, the lighting quality and efficiency goals of less than 1 watt per sq. ft. were achieved while meeting a budget of less than $3.50 per sq. ft.," says Bob Figuerido, electrical engineer and lighting designer for Compaq.

Figuerido also notes an unanticipated bonus: the perceived increase in ceiling height. "The gray furniture and silver gray fixtures create a depth of field that visually separates ceiling, lights and partitions three-dimensionally," he explains.

Dimming capability

In Longmont, Colo., T5-HO lamps were specified for the new, two-story, 130,000-sq.-ft. facility for the programmable-logic solutions provider Xilinx, Inc. In this case, the lighting design called for single-lamp indirect fixtures installed on 12-ft. mounting centers and suspended 21 in. from the ceiling, which provides approximately 30 footcandles to each cubicle. In addition, individual task lights are available in each cubicle for use as needed. Another row would have been required in some areas if T8 fixtures had been used—increasing labor, material and energy costs.

Tim Rohrbaugh, senior designer for Merit Electric, a full-service design build contractor based in Fort Collins, Colo., and the lighting designer on the job, notes that, all around, the goal of the lighting design was to save on energy and the T5 lamps were a key part of meeting that goal.

"Had we used dual-lamp T8 luminaires, approximately 25% more luminaires would have been required to provide uniform lighting," he asserts. "The final power density for the complete lighting system, excluding furniture-mounted lighting, is at a comfortable 0.9 watts per sq. ft."

In the spirit of energy efficiency, the Xilinx lighting design also includes the use of dimming controls, occupancy sensors and some daylight harvesting, other functions that the lamps are especially suited for.





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