When you choose the fixtures you will be using, it is well to keep four basic
ideas in mind. First, the location of work stations and the tasks performed in
an area are subject to frequent changes. The new lighting needs caused by
these changes can be met easily only when the system is flexible enough to permit
relocation of fixtures quickly, easily, and at low cost.
Second, the fixture should be an efficient source of light. As much light as possible should be able to get out of the fixture and onto the work surface. A fixture's efficiency is measured in terms of "coefficient of utilization." Manufacturers provide these data in their catalogs.
Third, the fixture should not be a source of glare. It shouldn't hurt your eyes when viewed in a normal work situation, such as when you are sitting at your desk or looking around the office. You shouldn't see the fixture or its lamps reflected on your desk or surrounding equipment, nor should light from the fixture create veiling reflections. Fourth, wherever possible, the heat generated by lighting fixtures should be integrated into the heating, ventilating, and air conditioning system to minimize energy use.
Fixtures that consume equal amounts of energy and provide the same amount of light output may not provide equal visibility of a seeing task. For example, a well shielded fixture can eliminate stray light that can hinder how well you can see. Likewise, there are certain fixtures that have been designed specifically to reduce veiling reflections, and many other types, each of which is designed for specific kinds of light control.
In addition to the overall design of the fixture, selecting the right diffusing material to let the light out of the fixture is important in determining its overall efficiency. Glass and acrylic prismatic lenses generally are more efficient transmitters of light than other materials, although some types of louvers that control the light distribution pattern of the fixture are equally efficient.
If you are considering a major lighting system overhaul of your lighting system, remember that you also must consider the relationship of lighting to your heating, ventilating and air conditioning (HVAC) system. In most cases, the heat generated by lighting was considered when your building's HVAC system was designed. This heat called "heat of light"comes from the lamps and ballasts. As room air passes over the outside of the fixture, it is warmed by the heat of light, thus increasing the temperature in the space.
There are techniques available for removing heat of light before it affects the conditioned space. Recessed air handling fixtures placed in the ceiling can capture and remove this heat before it becomes a problem. In some cases this heat can be used elsewhere in the building. This method helps avoid using still more energy.
There are two other factors that should be considered when choosing a lighting fixture. The first is the finish of the fixture, which should be suited to the environment of the space in which it will be located. If dampness or excess dirt is a consideration, your fixture's design and finish should minimize corrosion and accumulation of dirt. The second factor is the ease with which the fixture can be cleaned. It should not be difficult to remove the diffuser to get at the lamps and inside surfaces of the fixture.
