Like occupancy sensors, dimmer switches are connected to a relay panel. Preset
dimming controls from a relay panel provide predetermined dimming for several
channels or loads. Presets are tamper-proof, that is, they will not allow anyone
except authorized lighting control personnel to override the presets.
Dimming can be use to implement several energy-savings strategies. For
example, lights can be dimmed when the demand for electricity exceeds a
predetermined level, possibly as part of an overall load-shedding policy. Such
reductions are typically unnoticeable by most users.
Another example involves fluorescent lamps. The light output of fluorescent
lamps decreases over the life of the lamp (the expected depreciated output may
be used as an initial design factor). Dimming can be used with new fluorescent
lamps to produce the desired light level, then gradually manage the lighting
level over the life of the lamps to produce both a constant level of light output
as well as longer lamp life.
Daylight Harvesting
Photoelectric controls are designed to strategically use daylight to reduce the need
for artificial lighting, a process called “daylight harvesting.” They may be located
in perimeter offices, atriums, hallways or in areas with skylights. Ambient light
sensors measure natural and ambient light then based on the amount of natural
light, adjust the lighting to maintain a constant light level. In some spaces manual
or automatic blinds, or other means of reducing the direct solar exposure glare,
excessive light levels, and heat gain, can be used to supplement photoelectric
controls. These may include motorized window shades or blackout shutters.
Proper daylight-harvesting design not only includes providing adequate
daylight to an area but does so without undesirable side effects such as heat
gain and glare. Successful daylight-harvesting designs will incorporate shading
devices to reduce glare and excess contrast.
Window size and spacing,glass type, and the reflectance of interior finishes must
be taken into account as well. Despite all of these design considerations, daylight
harvesting provides little benefit without an integrated electric lighting system
due to the increased thermal loads from the sun. The electric lighting and
thermal loads must be reduced while simultaneously increasing daylight to an area.
Ballasts
An electrical ballast is a device that limits the amount of current in an electric
circuit. In electrical gas-discharge lights such as fluorescent and neon lights
ballasts control the current flowing through the light.
54 Smart Building Systems for Architects, Owners, and Builders