22 August 2006
CRITICAL DESIGN ISSUES:
Direct Glare: Lamps in the luminaire are shielded with louvers, perforations,
or lenses to avoid a view of the lamps and the resultant direct glare.
Luminances of Room Surfaces: Room surfaces need to be illuminated to
control the contrast between the occupant's task and the surrounding
surfaces in that person's field of view. This is especially important with
computer use when a person views a bright screen in the foreground. If the
background is too dark, the contrast will lead to eyestrain and fatigue.
Uniformity: Luminance uniformity should not exceed 5:1 in immediate work
surrounds, not including accent lighting.
Reflected Glare: When viewing tasks with a glossy finish, bright luminaire
components such as visible lamps or bright lenses reflect in the surface of
the task. This situation can make reading tasks annoying and at times
Source / Task eye geometry: Task areas and luminaire locations need to
be identified to avoid shadows and direct and reflected glare.
Target Horizontal Illuminance ( 10%): 300 lux (30 fc) ambient, 500 lux (50
fc) on the task
A task/ambient approach to the lighting in an individual office results in separate control
over an ambient system (typically a pendant mounted direct/indirect luminaire) and task
lighting (a desk or undercabinet light). In larger offices or interior offices, additional
wallwashing may be necessary to add wall surface brightness. By providing a high
illuminance level on the task only and not the entire room, energy is saved in the
ambient system, which does not have to produce as much light. This approach also
provides a comfortable and flexible lighting environment.
Control devices could be as simple as manual on/off or dimming of the separate
systems. Occupancy sensors (individual or incorporated into wall switches) save
additional energy when someone is not in the office.