Daylight Control

A light shelf (Fig. 33-4) is a construction that cuts horizontally through a window and bounces sunlight into the room without glare. Light shelves shade glazing from direct sun, and reflect daylight onto the ceiling of the room. Both the direct sunlight and diffuse light from the sky are distributed indirectly deeper into the space. The light shelf shades the glazing below it from direct sun, but leaves ground-reflected light near the window. It increases uniformity of illumination by increasing daylight farther toward the back of the room while decreasing the amount of light near the window. Groups of parallel opaque white louvers are used in a similar way. Louvers and light shelves may let some sun filter in with lower winter angles, but cut glare. Light shelves can be used to keep light glare off computer screens.

Trying to resolve problems with the orientation of the building with mechanical shading devices rather than by proper building design is prone to problems. Bill Lam cites Oscar Niemeyer's Ministry of Education in Brazil, which faces east and west, as an example. Heavy exterior crank blinds were installed to block the intense sun, resulting in a very dark interior. The blinds ultimately rusted and had to be removed. Reliability is most important in selecting movable shading devices, or they won't be adjusted or used.

There are many types of shading and reflecting devices for controlling the sun's heat and glare. Trees and vines cool as well as shade, and deciduous plants admit more light in winter when they lose their leaves. Overhangs block or filter direct sunlight and allow only reflected light from the sky or ground to enter the window. Overhangs necessitate early planning and coordination between architects and interior designers. Awnings and shutters provide adjustable shade, and can be manually, mechanically, or automatically controlled.

Horizontal louvers on southern exposure windows work well to reflect light onto high-reflectance ceilings. Vertical louvers are effective for low sun angles on east and west facing windows. Eggcrate louvers, which have both horizontal and vertical elements, block both high and low sun angles, and reflect daylight into the space.

Figure 33-4 Light shelf.

Louvers convert direct sun to softer, reflected light and can reduce the apparent brightness of large areas of sky. Exterior louvers are usually fixed, but some can be raised up out of the way when not needed.

Venetian blinds adjust to changing exterior and interior conditions. Venetian blinds can block all daylight and view if desired. They permit light to enter the room by reflection back and forth between the slats, while still blocking glare. Venetian blinds can exclude direct sun and reflect light onto the ceiling, where it will bounce into the interior. When mirrored on one or two sides, they redirect daylight more deeply into the room. In the upper 61 cm (2 ft) of the window, they can beam daylight 9 to 12 meters (30-40 ft) into the space to provide illumination at the work surface. It is possible to rig blinds to cover only the lower half of the window. Units are available with slender blinds between two window panels, eliminating dirt and clumsy control strings.

Roller shades diffuse direct sunlight, eliminate glare, and increase the uniformity of illumination. When illuminated by direct sun, they can be so bright that they become a source of glare themselves. Off-white fabric colors or additional opaque drapery can be used to reduce brightness. If pulled up from the bottom of the window, opaque shades can eliminate glare while still permitting daylight into the room.

When blinds or shades are controlled individually and manually, blinds may be raised or lowered to different heights from window to window, and the appearance of a building facade may suffer. Automatic motorized shading systems that respond to sensors and constantly adjust the amount of daylight are usually impractical in all but the highest-end installations because of their substantial cost.

The effectiveness of draperies for sun control depends upon the weave and the reflectivity of the fabric. Any amount of light transmission, from blackout through transparency, can be achieved. Even more flexibility is available with two separately tracked drapes over the same opening. Shades and curtains allow user adjustment and soften the interior environment. For maximum effectiveness, the exterior surfaces of shades, drapes, blinds, and insulating panels should be mirrored or highly reflective.

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