To use of sunlight as a source of ambient illumination can cause glare and heat gain. These can be controlled with shading the openings. Shading devices can be categorized as horizontal, vertical, or a combination, often referred to an egg crate. All forms work best at the building scale, where they have an architectural impact and reduced obstruction of views.
Horizontal devices provide shade based on the altitude angle of the sun. Most commonly seen in the form of overhangs, they are particularly effective for shading north and south building elevations. Horizontal devices let in low angle sunlight and block high angle sunlight. This can be good for buildings which can benefit from winter (low-angle) heat gain.
Vertical devices provide shade based on the bearing angle of the sun. Their effectiveness varies daily, as the sun moves around the horizon.Vertical devices have the ability to block low-angle sun, and consequently the often used on openings facing east or west. Blocking the low angle sun, also blocks views. Adjustable vertical devices can be responsive to the changes in sun angle.
Sunlight Redirecting Devices
Sunlight redirecting devices have similar geometric patterns to those of shading devices. Redirecting devices should be oriented to receive maximum illumination and to redirect the light to locations within the space.
Light shelves are horizontal shading and redirecting devices. They improve the uniformity of natural light in a space by reducing the the level of illumination near the window and redirecting light deeply into space. For best distribution, light shelves should be located as low in a space as possible without causing glare, typically above standing eye level. Improve the effectiveness of light shelves by increasing the ceiling height.
To be effective minimum depth of a light shelf is determined by shading requirements. To prevent glare conditions, direct light from upper window should not penetrate past the edge of light shelf. Uniformity of light distribution can be improved by extending the depth of the shelf.
Projecting light shelves also provide additional shading for the lower window. Light shelves are typically level; sloping them downward outside will make them more efficient as shading devices, but less efficient at distributing light. Sloping the shelves toward interior does the opposite; they become better at distributing light, but less efficient as shading devices.
A technique combining both features is a level light shelf with an inward sloping wedge added to the leading edge.This has the effect of pushing high angle sunlight more deeply into space. See sketches below. This feature can be very beneficial, because light shelves typically provide less light when sun is high (summer) than when sun is low (winter).
Light shelves are most effective on the south side as shown below for various climates. Light shelves are not useful for light distribution on north side, but they do not substantially reduce illumination and may make views more comfortable by blocking sky glare.
Design of Suncatchers
Suncatchers are vertical sunlight-redirecting devices parallel to the building facade. As vertical devices, they are best for intercepting low-angle sunlight on the east and west side of buildings. Suncatchers shade low angle sun and may block views. Light they catch tends to be reflected downward, witch can result in glare. So they should be used to redirect light to ward walls or with a light shelf, to redirect the light toward the ceiling.
Follow us on our next article “ Toplighting ”.
Architectural Lighting by M. David Egan and Victor W. Olgyay