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Redirecting light is the use of building elements to bounce sunlight into more desirable locations in the building. Light shelves and baffles are two strategies that can distribute light more evenly.
To evenly distribute light, it is often desirable to bounce sunlight off of surfaces. Direct sunlight on work surfaces often causes glare. Light shelves are devices that both shade view windows from glare and bounce light upward to improve light penetration and distribution.
A light shelf is generally a horizontal element positioned above eye level that divides a window into a view area on the bottom and a daylighting area on the top. It can be external, internal, or combined and can either be integral to the building, or mounted upon the building.
A light shelf avoiding glare and pulling daylight deeper into the room
Light shelves are most effective on walls facing the sun's path; on pole-facing walls they simply act as shades. Light shelves on east and west orientations may not bounce light that much further into the spaces, but are an effective means of reducing direct heat gain and glare.
Exterior light shelves reduce daylight near the window but improves the light uniformity. The recommended depth of an external light shelf is roughly equal to its height above the work plane.
To reduce cooling loads and solar gain, an exterior light shelf is the best compromise between requirements for shading and distribution of daylight. Because they are only shades, they do not change the ratio of incoming light to heat, but better distribution of light can reduce the amount needed in a space, which helps with cooling.
Light shelves may be constructed of many materials, such as wood, metal panels, glass, plastic, fabric, or acoustic ceiling materials. Considerations that affect the choice of material include structural strength, ease of maintenance, cost, and aesthetics.
Light shelves and vertical fins do not need to be opaque; when they are transparent but diffusive, they can help evenly distribute light without reducing the total amount of light significantly.
Diffusing glass fins on a west-facing wall help distribute light evenly without reducing incident light.
Sizing Light Shelves
The orientation, height, position (internal, external, or both), and depth of the light shelf are critical. A rule of thumb is that the depth of the internal light shelf be approximately equal to the height of the clerestory window head above the shelf. The optimal width and placement of light shelves depends on the site's location and climate.
When light shelves are oriented vertically, they are known as baffles. They are used with skylights or roof monitors to better distribute daylight and avoid glare. Designing the optimal height and placement of baffles is done the same way as designing light shelves.
Baffles in a roof monitor avoid direct glare while bringing in the sun's full brightness