Fixtures That Can be Aimed
At present, aiming fixtures are available as standard equipment only for incandescent lamps. Compact fluorescent lamps can be used in many incandescent fixtures in a way that provides adequate illumination levels and beam control for task lighting. However, compact fluorescent lamps are too small in frontal area to avoid shadowing.
To explore task lighting with fixtures of large surface area, Wulfinghoff Energy Services, Inc. conducted experiments with a variety of fixtures. By far the best results were obtained by using two large parabolic aluminum photoflood fixtures for each task area. These reflectors have some surface etching to soften the beam. The fixtures were installed on opposite sides of the viewer, just below the ceiling, in the “standard” task lighting configuration described previously. Each photoflood fixture used one 23-watt screw-in fluorescent lamp. The combination of a compact fluorescent lamp inside a deep reflector fixture works well because the lamp emits most of its light perpendicular to its axis, so there is little direct light from the small lamp in comparison with the light coming from the reflector.
In experiments conducted in a typical office, the beam of each reflector was aimed at its respective side of the desk. The beams overlapped, providing illumination that was essentially uniform within the task area. The average illumination level was about 25 footcandles (250 lux), which was more than adequate for typical office paperwork and word processing. (25 footcandles is considered a low illumination level for office work in the United States, but not in most other countries. This illustrates that illumination levels can be reduced substantially if glare and veiling reflections are eliminated.) Shadows were light and diffuse. There were no bright reflections in the computer screen or elsewhere, but the screen had a light haze from being directly illuminated by the fixtures. Visual comfort remained good over a test period of several weeks. There was no discomfort when facing either side of the desk. lamp. The combination of a compact fluorescent lamp inside a deep reflector fixture works well because the lamp emits most of its light perpendicular to its axis, so there is little direct light from the small lamp in comparison with the light coming from the reflector. In experiments conducted in a typical office, the beam of each reflector was aimed at its respective side of the desk. The beams overlapped, providing illumination that was essentially uniform within the task area. The average illumination level was about 25 footcandles (250 lux), which was more than adequate for typical office paperwork and word processing. (25 footcandles is considered a low illumination level for office work in the United States, but not in most other countries. This illustrates that illumination levels can be reduced substantially if glare and veiling reflections are eliminated.) Shadows were light and diffuse. There were no bright reflections in the computer screen or elsewhere, but the screen had a light haze from being directly illuminated by the fixtures. Visual comfort remained good over a test period of several weeks. There was no discomfort when facing either side of the desk.
In summary, this arrangement provided illumination of high quality with an energy expenditure of only 50 watts per work station.
Good results were also achieved using a pair of industrial-type skirted fluorescent fixtures for each work station. The fixtures were fitted with brackets to allow aiming, and were installed just below ceiling level. Each fixture has two 24-inch, 20-watt tubes, for a total power of about 100 watts per work station. The illumination level was somewhat lower, about 20 footcandles (200 lux), which was satisfactory for routine word processing. The fixtures spread light well outside the task area, which was a desk of normal size. This factor accounts for the lower illumination level. The illumination was uniform and pleasant.
These experiments demonstrated the feasibility of task lighting for general office work using aiming fixtures. They also showed that fluorescent task lighting fixtures can be produced at low cost. If appearance is not a major factor, task lighting fixtures can be adapted from fixtures that are readily available.
Note that fluorescent and HID lamps may have limitations in mounting position. These are explained in Subsections 9.2 and 9.3, respectively.