In November we began a discussion on daylighting and continue looking into that subject this month. When looking at daylighting, an integrated design balances the cooling load of the window against required daylight illumination levels, thereby capturing both cooling and lighting energy savings without creating discomfort. A poor design imposes a substantial cooling load and creates glare. Achieving this balance requires careful and informed design and engineering.

Daylighting requires the participation and cooperation of multiple disciplines — architecture, lighting design and mechanical system design in conjunction with proper glass selection. Even when the proper components are selected, poor design and commissioning practices often lead to unreliable performance and uncomfortable work environments.

Control the Glare

Glare from natural sunlight can offset any positive attributes of daylighting. Glare will contribute to eyestrain and reduced productivity. Care must be taken in how daylight is allowed into the building without causing glare.

Some design elements may include:

• Exterior sunshades – Effective on south facing elevations only and may not have a positive effect during the winter months when the sun is low in the sky;

Image courtesy of Tubelite Inc.

• Translucent (as opposed to transparent) glazing – Very effective when used in skylighting applications;

• Light redirecting systems – Light louvers or light shelves are effective at both controlling the glare as well as redirecting light toward the ceiling;

Image courtesy of LightLouver LLC

• Manually or automatically controlled blinds – Consider blinds between the glass to avoid damage and eliminate cleaning; and

Image courtesy of Wausau Window and Wall Systems

• Electrochromic or thermochromic glazing – Tints the glass either electronically or by natural solar heat.

Image courtesy of SAGE Electrochromics