A high-quality lighting solution for office workers could be to use suspended direct/indirect lighting with fixtures mounted over workstations and a downlight component of the fixture that is individually dimmable by the user.

Multiple research studies have linked these choices with comfort and satisfaction. Higher lighting satisfaction, in turn, has been linked to greater likelihood that workers “rate the space as more attractive, are happier, and are more comfortable and satisfied with their environment and their work,” according to the Light Right Consortium.

Two 2002 studies involving 288 participants in a simulated office environment in Albany, N.Y., found that about 70 percent of respondents rated a fairly typical 2-by-4 parabolic recessed troffer layout as comfortable, which rose to 80 percent for a suspended direct/indirect layout. These results confirmed previous research.

Direct/indirect fixtures combine the advantages of both types of distribution. The direct component provides modeling definition and focused illumination on the task, while the indirect component provides visually comfortable ambient lighting. Illuminating ceilings and walls can make a room appear brighter and more spacious.

The Albany studies further found that, by dedicating a single overhead direct/indirect fixture to each workstation and giving users control of their task light levels, the fraction finding the lighting comfortable rose to about 90 percent.

Lighting systems are typically designed on a one-size-fits-all basis in terms of light level, but people exhibit different preferences. According to the 1999 Steelcase Workplace Index Survey, three out of four office workers want more control over their lighting, with about half saying they want the ability to adjust light levels using a dimmer switch.

In a suspended direct/indirect design, these office workers can be satisfied by positioning fixtures directly over the workstations and then giving each occupant the ability to dim the direct lighting component of their fixture using a readily accessible control.

In 2010, the National Research Council Canada—Institute for Research in Construction published the results of a real-world open-office lighting study, based on the lighting perceptions of 1,750 occupants. These buildings underwent a retrofit from parabolic recessed troffers to dedicated suspended direct/indirect with personal dimming control. The results confirmed previous research, with 65 percent of respondents finding the parabolics to be comfortable and 100 percent finding the new individually controllable direct/indirect design to be comfortable.

The researchers found: “The workstation-specific luminaires with individual control were rated as providing lighting that was better than in other similar workplaces … . Pleasure, room attractiveness and illumination, lighting satisfaction, overall environmental satisfaction, job satisfaction and organizational commitment were all higher for the people in offices with workstation-specific luminaires.”

This lighting and control scheme is more sophisticated than traditional designs that emphasize direct distribution on horizontal surfaces and automatic shutoff control. An individually zoned, dimmable ballast would be required with an appropriate user interface. However, installation of the dimming ballast presents the opportunity to integrate additional control inputs to maximize, energy-cost savings and make the investment more profitable.

In 2007, National Research Council Canada published another study, based on data collected over the course of a year from a real-world open-office environment, that not only put the benefits of personal dimming to the test, but also explored energy savings potential through integrated control.

Four years prior to the study, the building had installed 195 suspended direct/indirect lighting fixtures to replace 530 recessed, 2-by-4, T8, deep-cell, parabolic fixtures. The new fixtures, centered over the workstations and containing 3-by-32-watt T8 lamps powered by two electronic ballasts, reduced installed lighting wattage by about 40 percent.

Dimmable ballasts controlled each fixture’s direct distribution (two outboard lamps) along with user controls and onboard occupancy sensor and photosensor. The occupancy sensor monitored the workstation and dimmed the direct lighting component to “off” after detecting no one around. If the sensor detected occupancy, it signaled the ballast to start the lamps and restore light output to the last user-set level. The photosensor monitored light levels reflected from the task, which received daylight contribution through windows and dimmed the direct lighting component when a target threshold was reached. The indirect lighting component, meanwhile, remained on at 100 percent to provide ambient illumination throughout hours of occupancy.

The result was average energy savings of 42–47 percent, while correlating with higher occupant job and environmental satisfaction. Overall, the direct/indirect design with integrated controls produced 67–69 percent energy savings compared to the parabolic design. If installed alone, the occupancy sensors would have produced an estimated average of 35 percent savings; daylight harvesting, 20 percent; and personal dimming control, 11 percent.

Although more sophisticated, this setup provides a lighting option that can save significant amounts of energy and enhance worker job and environmental satisfaction, with associated economic benefits.


DILOUIE, L.C., a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.