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mit the most heat in summer, adding to the cooling load. Horizontal skylights need shades where artificial cooling is used. Controlling brightness and glare may also require louvers, shades, or reflector panels. Horizontal skylights don't collect much solar heat in winter, are covered by snow, and inevitably leak in rain. Horizontal skylights work best in overcast conditions. However, where an angled skylight may not be possible, a well-designed and installed horizontal skylight with a domed surface can bring daylight into an interior space and provide a view of sky.

Skylights are glazed with acrylic or polycarbonate plastic, or with wired, laminated, heat-strengthened, or fully tempered glass. Building codes limit the maximum area of each glazed skylight panel. Building codes also require wire screening below glazing to prevent broken glass injuries when wired glazing, heat-strengthened glass, or fully tempered glass is used in multiple-layer glazing systems. There are exemptions to these regulations for individual dwelling units. Double-glazing a skylight promotes energy conservation and reduces condensation. Skylights with translucent glazing provide daylight from above without excessive heat gain. The way that translucent materials diffuse light reduces contrast for a restful long-term environment, but the light appears as dull as that from an overcast sky. Clear glass should be used where you want the sparkle of sunlight.

Other Toplighting Options

Light pipes were first introduced in the early 1990s. They are basically a metal or plastic tube that delivers light from the roof into an otherwise dark room. The typical light pipe includes a roof-mounted plastic dome to capture sunlight, a reflective tube that stretches from the dome to the interior ceiling, and a ceiling-mounted diffuser that spreads the light around the room. There are a number of brands currently on the market. Most companies offer two sizes: a 33-cm (13-in.) model to fit between 41-cm (16-in.) on-center framing, and a 53-cm (21-in.) model to fit between 61-cm (2-ft) on-center framing. Tests done by the Alberta Research Council in Canada found a light pipe's output to be the equivalent of a 1200-W incandescent lamp. Light pipes won't give a view, but will bring light to spaces where a skylight won't, including walk-in closets, small interior bathrooms, and hallways. Installation is relatively simple.

Roof monitors (Fig. 33-3) reflect daylight into a space. The light enters a scoop-like construction on the roof, and bounces off the surfaces of the monitor opening and down into the space. Mirror systems using a

Skylights (Fig. 33-2) allow daylight to enter an interior space from above. Skylights are metal-framed units pre-assembled with glass or plastic glazing and flashing. They come in stock sizes and shapes or can be custom fabricated. They are efficient and cost-effective sources of daylighting.

Skylights can be mounted flat or angled with the slope of a roof. Skylights that are angled on a north-facing or shaded roof avoid the heat and glare associated with direct sun. The angled sunbeams can be bounced off angled interior ceilings to further diffuse the brightness. Angled skylights can also sometimes offer a view of sky and trees from the interior.

Horizontal skylights get less of the low-angle winter sun than skylights on sloped surfaces, minimizing their contribution to cold weather heating. They also ad-

Monitors protect from direct overhead sun, and allow indirect sun to bounce off interiors and diffuse into space.

Figure 33-3 Roof monitor.

periscope-like device can bring daylight and views underground by reflecting them down through the space.

Roof windows are stock wood windows designed for installation in a sloping roof. They either pivot or swing open for ventilation and cleaning. They are typically 61 to 122 cm (2-4 ft) wide and 92 to 183 cm (3-6 ft) high, and are available with shades, blinds, and electric operators. Sloped glazing systems are essentially glazed curtain walls engineered to serve as pitched glass roofs.

Active techniques for daylighting include heliostats and tracking devices. A heliostat is a dish-shaped mirror that focuses sunlight onto a stationary second mirror. It dynamically readjusts the primary mirror to track the sun and maximize the capture and use of sunlight at all times of the day. Once the light is captured, it is distributed, often with a light pipe. The downside to this device is that it must be maintained to prevent dirt and dust accumulation from affecting its performance, and it requires a source of energy (perhaps solar).

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