Window Covering Design

The selection of blinds, window coverings, or the lack thereof is likely the most crucial choice a designer will make when seeking to ensure visual comfort while maintaining daylight performance over time. We have all seen buildings where blinds are down continuously. Typically, this is associated with visual discomfort (glare). The most common source of glare issues in daylighting is a line of sight to the disk of the sun. Selecting a window covering that is opaque enough to block the sun, such as fabric window shades with 3% or less openness or horizontal blinds, can control this phenomena.

Manually operated blind systems can be very effective if properly used. More specifically, a 2" horizontal blind with a white finish can function as a series of mini light shelves casting indirect light into the space when desired. However, they rely on and require constant user attention to maintain complete glare control while achieving maximum daylight performance. For this reason, blinds or shades are often permanently deployed at the ¡°worst case scenario¡± position to maintain visual comfort throughout the day and year. This typically results in poor daylight performance and the elimination of views to the exterior.

Automated glare control has the distinct advantage of being deployed only when needed and retracting without user intervention when direct sunlight is no longer present to allow for unimpeded diffuse daylight. In most cases, this will deliver longer periods of effective daylight contribution, increased electric lighting power savings, and longer durations of unobstructed views to the exterior. Automation of glare control may provide the most persistent daylight performance where low angle direct sun is present during extended periods of occupancy.

Shading and Exposure Tips:

• North - Shading may only be needed in early morning or late afternoon.
• South - Good access to strong illumination but varies throughout the year. Shading is easier than East/West.
• East/West - Shading is difficult but critical for comfort.