The Science of Light
Oct 1, 2009 12:00 PM, By Amy Keller Gleed
The benefits of daylight modeling: a site-specific simulation that aids the process of intelligent daylighting design.
Light evaluation
One of the first steps in designing a space is to evaluate the effect of direct beams of sunlight. In educational settings, such as classrooms or libraries, balanced daylighting is essential for ambient light levels.
Figure 1 shows an example of a design submitted for daylight simulation. The architect asked for help in selecting light transmittance for the skylights. The model was run with different glazing options, and it provided the designer with information to help meet the target luminance for the space below.
First to be assessed was the skylight at noon on the equinox (Sept 21st); the sun is overhead where it is strongest and gives a good indication of typical light levels midday in the space for most of the year (noon in summer months is higher as the solar angle is more direct; winter months have a lower sun angle at noon). Using 30 percent glass for the skylight results in uneven light levels, as direct sunlight is not controlled. Shown here is a false-color plan view, which reveals excessive areas of direct sun (shown in bright yellow); light levels are not balanced within the space. This highlights the glare problem caused by sunlight coming through the glass.
An alternate toplighting strategy then was considered, changing to translucent sandwich panels to manage the direct beam penetration. This analysis is based on 8 percent light transmittance. Figure 2 shows the new plan view for the same space. Given the same sky condition, the translucent sandwich panels diffuse direct sunlight to fill the entire space evenly with controlled, balanced daylight.
Had the original plans been executed, the results would have been disappointing. Students and staff would have had difficulty dealing with imbalanced light levels and glare. Thanks to daylight simulation, alternatives were considered and decisions made that resulted in a more effective design and a more comfortable space. Balanced daylighting also will generate operational savings through reduced HVAC loads and electric consumption.
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