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Practical Daylighting
Use of large glazed openings does not guarantee good daylighting. One of the biggest challenges of daylighting is to provide illumination in areas where it is most needed, for instance on northern exposures, and on ground levels of buildings. There are several devices and architectural design techniques that achieve a desired quality and quantity of daylight. The devices serve three general functions: to redistribute sunlight by diffusion or reflection, to eliminate excessive illumination on interior surfaces, and to eliminate glare and direct radiation.

Tubular skylights collect and transmit natural light to areas difficult to light, such as buildings, with drop ceilings, lower floors of multi-floor buildings, museums and laboratories.

Daylighting falls into two general categories: sidelighting and toplighting.

For buildings with long, shallow floor geometries, it is feasible to daylight up to 70 percent of the footprint with a sidelighting system relying on ceiling-height glazing in perimeter walls. Effective daylighting requires a ceiling height of at least nine feet, and ceilings of 10 feet, or higher, are recommended.

Toplighting—through roof monitors, clerestories, skylights, sawtooth elements and atria—provides natural light through rooftop openings and their orientation is not dependent upon the building orientation. Clerestories use rooftop glazings that run parallel to vision glazing on perimeter walls. Sawtooth components incorporate a series of vertical or sloped glazed elements separated by sloped roof elements.

A technique known as reflected (or beam) daylighting, redirects daylight from one portion of a building to another. One method is to mount reflective blinds in the upper two feet of a vertical window. Another is to install reflective shelves at the base, inside or outside, of a window. Exterior window overhangs with downward-facing reflective surfaces also transmit light reflected from the ground or other structures into interior spaces. This reflected daylight does not cause glare or overheating.

Various exterior features limit excess direct or diffuse sunlight. Overhangs projecting from a building’s roof or exterior wall can shade windows. The depth of the overhang can be designed to block direct sunlight and to reduce heat gain in the summer, but still allow direct sunlight into a building to provide heat in the winter. Overhangs may be solid or opaque, and use flat or sloped designs. Fixed and movable exterior baffles or louvers running horizontally or vertically across windows can be used to reflect and diffuse sunlight. “Shading is the critical element in this equation,” says Loisos.

Fixed and movable interior features such as drapes, blinds, louvers, and baffles, can block and reflect direct sunlight entering through windows. Reflective baffles, located inside roof monitors or along the ceiling plane, redirect or diffuse sunlight entering through a monitor. Louvers may be necessary to control skylight glare and solar heat gain.

Tubular skylights consist of angular tubes that direct and transmit light to areas where it is needed. The tubes contain reflective surfaces that direct daylight entering the tube down or horizontally into building interiors. Tubular skylights can provide high quality light with little heat or glare. They are useful in areas that are difficult to light, and in buildings that have special lighting requirements, such as laboratories and museums. They can also provide “skylights” for the lower floors of multi-floor homes or buildings.