22 August 2006
ceilings and 50% or greater for walls)20.
ACTIVE DAYLIGHTING. Active daylighting strategies and devices utilize a
mechanical component to collect and distribute daylight. Such devices differ from the
passive strategies that have previously been discussed which are stationary. The
example shown in figure 4-10 turn a series of reflectors as the sun moves throughout
the day. These reflectors catch the direct sunlight and redirect it through the skylight.
Such devices add extra initial cost and also pose additional maintenance
issues. However, they also can make use of daylight for a longer period of time
throughout the day. With tracking devices, effective daylighting can begin earlier in the
morning and last later in the day than with stationary skylights. Careful evaluation of the
lifecycle cost and the energy savings must be considered.
Figure 4-10. Example of an active daylighting system that tracks the sun and
directs daylight into the building.
PHYSICAL MODELING. Daylight levels depend on many factors such as
window shapes, orientation, shading, and time of day. Therefore, physical models built
to scale can provide information on light quality, shade, shadows, and actual light levels.
By building the model with the actual proposed materials and orienting it with
adjustments for latitude, season, and time of day, the light quality can be seen in the
model. Such models inform the designer about quality issues including light patterns,
shade, shadows, contrast, and penetration in the space. An illuminance meter inside
the model will provide accurate predictions of expected light levels in the building.
COMPUTER SIMULATION. A wide range of software programs model the
sun's path and its impact on building geometry in addition to how it affects heat gain and
"Office Lighting", Lighting Handbook Reference and Application, Chapter 11, Ninth Edition (New York:
The Illuminating Engineering Society of North America, 2000), p. 11-2.