Indirect Lighting
Indirect lighting includes cove lighting, valance lighting, wall washers, and bounce lighting. Indirect lighting wastes energy by requiring light to be reflected repeatedly on the way from the lamp to the activity. A fraction of the light is lost at each reflection.
Even the most reflective surfaces absorb some light. For example, clean white paint has a reflectivity of about 90%. If light must reflect three times from such a surface, somewhat less than one third of the light is lost. If a the surface is dirty or has a pastel color, its reflectivity is reduced to about 60% to 80%. In this case, three reflections will result in well over half of the light being lost.
Eliminating cove and valance lighting may leave the walls too dark, especially if they have decor. The solution is to install ceiling fixtures near the wall that have enough lateral distribution to highlight the walls
reflections will result in well over half of the light being lost. Eliminating cove and valance lighting may leave the walls too dark, especially if they have decor. The solution is to install ceiling fixtures near the wall that have enough lateral distribution to highlight the walls.
Eliminating cove and valance lighting leaves a dark slot. You can cover this with a decorative frieze. If you want to create the appearance of illumination coming from the slot, you can create this effect with much less power by installing low-wattage lamps behind a translucent panel that covers the slot. Or, if you have budget for deco, install a neon tube along the slot.
Bounce lighting can be reasonably efficient if it involves only a single reflection. For example, you can use upward pointing HID lamps to reflect light off a white ceiling to provide area lighting. Make the surface very reflective. See Measure 9.6.2 about using bounce light for task lighting.
Fixtures Installed in Ceiling Plenums
In some commercial buildings, you may find fluorescent strip fixtures installed in the ceiling plenum, illuminating the space below through grilles installed in a suspended ceiling. This arrangement is especially inefficient. It traps most of the light that does not pass directly from the lamps through the opening. Such arrangements are usually installed for appearance, but they are not particularly attractive. Figure 5 shows an example.
To eliminate the energy waste while maintaining a flush ceiling, simply install flush-mounted fluorescent fixtures that have efficient reflectors. Surface-mounted fixtures also provide greater flexibility in fixture location and light distribution.