Sustainable Building Technical Manual - Etn-presco.net

installations require diffuse glazing for solar control, they do not provide views tothe outside. When skylights are used in a daylighting strategy, be sure to:– Angle light wells to prevent loss of efficiency. The finished vertical surfaces belowthe skylight opening are known as the “light well.” As the depth of the constructionor the distance from the roof to the ceiling plane increases, it becomes more importantthat the light well be angled to prevent loss of efficiency of the skylight system.– Use baffles below the skylight to reflect some of the incident light up onto theceiling surface. This technique reduces the ratio of source-to-background contrastby making the ceiling a relatively large indirect light source.– Consider roof design. When a skylight is used in conjunction with a sloped roof surface,the efficiency of the skylight is reduced in proportion to the slope of the roof,and the light distribution pattern becomes more like that of a sidelighting strategy.If the slope of the roof is to the north, solar control is less of a concern; if it is to theeast, south or west, it is more of a concern.Light Distribution Strategies❑ Use sloped or curved ceiling planes.Ceiling shape is the simplest mechanism for distributing light in a space. Slopingthe ceiling from a high point at the window or skylight essentially has the sameimpact as maintaining a high ceiling throughout the space. Curving the ceiling canproduce dramatic effects. The light from the window or skylight can be focused orcollimated in the case of a concave surface or further diffused and spread in thecase of a convex surface.❑ Optimize overhangs based on window height and latitude (solar altitude).Although usually necessary to exclude light and solar gain at unwanted times, overhangsalways reduce the overall amount of daylight in the space and should thereforebe designed with care, including an analysis of their year-round effect.❑ Incorporate light shelves with windows where appropriate.The light shelf is an extremely useful tool when used in conjunction with sidelightingstrategies. This mechanism, a horizontal surface at or above eye level, serves to reflectlight falling above the vision window up onto the ceiling and therefore deeper intothe room (Figure 5). At the same time, it reduces illumination immediately adjacent tothe window, where illumination levels are typically too great to work comfortably.This has the effect of creating more even illumination throughout the space, eventhough the overall amount of light flux into the space is reduced.❑ Employ baffles, louvers, and reflectors as appropriate in conjunction with any ofthe above mentioned strategies for solar control.❑ Integrate daylighting with luminous ceiling systems.Locating clerestories and skylights above luminous ceiling systems provides a uniquemethod of integrating natural and electrical light sources. However, increased maintenancemay be a concern.Innovative Sidelighting SystemsThe primary challenges in sidelighting applications are: (1) the need for control of solarlight and heat gains near windows; and (2) the transfer of light to the deeper zones awayfrom the windows in order to extend the effective depth to which daylighting may beachieved. The following innovations can address these issues.❑ Consider using the currently available techniques:– Solar optic lens film (SOLF) applied to acrylic panels;– Molded acrylic prismatic glazings or prismatic panels;– Specular blinds or mirror panels;– Holographic or diffraction-grating glazings; and– Reflective films.