Updating lighting design for energy efficiency.

Aesthetics, cost, and performance are the traditional criteria by which lighting designers select components and systems. Energy efficiency has fast become the fourth criterion.

To enhance the marketability of their real estate properties, New York City building owners are being compelled to invest in energy-efficient lighting systems because of the need to reduce operating overhead, the introduction of new energy codes, and the availability of attractive utility rebates.

What constitutes energy efficiency depends on the point of reference. While New York State's energy construction codes allow 2.4 watts per square foot in offices, Con Edison's "New Construction" rebates require less than 1.7 watts per square foot. Yet, the offices of both the Natural Resources Defense Council (NRDC) and the National Audubon Society were designed at less than 1 watt per square foot.

According to the New York State Energy Research and Development Authority, the use of energy-efficient lighting systems in commercial office buildings can generate savings from 35 to 40 percent. Energy-reducing lighting technologies can also facilitate eligibility for utility rebates and shorten the investment payback period to less than two years. In addition, actual benefits can include improvements to the work environment. For the past 30 years, a typical lighting scheme consisted, for the most part, of a uniform lighting layout using a grid of 2-by-4 fluorescent fixtures that consumed at least 3 watts per square foot. Current energy-reducing lighting designs call for a task/ambient system, with ambient or general lighting at low but comfortable levels, and user-controlled task lighting at each workstation. For example, at Crown Home Furnishings' new 65,000-square-foot showrooms on New York's Park Avenue, perimeter offices have a task/ambient lighting plan with ambient light provided by recessed indirect/direct fixtures in the ceiling and task lighting mounted under wall-hung units.

The plan also incorporates the concept of "shared or borrowed lighting." This is accomplished using a recessed wall-wash cove system along the inside common wall between private offices and corridors. The system has dual benefits. Interior office light levels are supplemented and the outside corridors are illuminated by light spilling through frosted-glass clerestories and sidelites in the office/corridor wall, thereby eliminating the need or expense of ceiling-mounted fixtures.

After the selection of fixtures, the most important energy-saving tool is lighting control. NRDC, for instance, cuts its energy consumption in perimeter offices to half that used in core offices just by switching off lights and making efficient use of daylight. A more sophisticated system would incorporate automatic controls with light sensors that adjust artificial light levels to compensate for available daylight.

Studies show how effective occupancy sensors are as an energy-saving tool, whether wail mounted within a private office or linked together on the ceiling to form zones in an open-area plan. By limiting the use of light to the hours of occupancy, these lighting controls can provide as much as 30 percent savings.

Substituting compact fluorescent lamps for incandescent can greatly reduce energy costs. Such was the case in the expansion and renovation of St. Bernard's School library in Manhattan. To make the school's lighting scheme more energy efficient, the mostly incandescent plan was changed to an all compact fluorescent scheme, thereby cutting the expected annual energy costs from $2,500 to $900. To increase illumination in the bookstacks, fluorescent wall washers were added, and under-shelf task lighting was specified to boost brightness levels in reading carrels. Multilevel switching was employed to turn off fixtures along the library's exterior windows when natural (daylight) lighting was sufficient.

Complete retrofit of existing fixtures is another solution for reducing operating costs. This is exactly the tack Dean Witter took with Fuji Corp.'s offices in Elmsford, New York. To update Fuji's lighting systems, four components were replaced. The out-dated prismatic lens was replaced with a glare-free, custom-designed 24-cell, 3-inch deep parabolic louver, significantly enhancing user comfort; the original 40-watt cool white lamps were replaced with 34-watt tri-phosphor fluorescent lamps, thereby improving color rendering; specular reflectors were installed inside the fixtures to reflect light from the lamps down and out, thus avoiding wasted "trapped" light; and standard magnetic ballasts were replaced with more energy-efficient electronic ballasts.

As a result, the retrofit system's light output is approximately equal to that of the original. Energy usage has been reduced from 136 to 57 watts per fixture. Fifty-two percent of Fuji's capital expenditure has been recouped through Con Edison's rebate program. The remaining 48 percent will be paid back in energy savings in less than two years. And, the retrofit was accomplished in approximately three to four weeks, with little or no disruption in the workplace.