Few design elements are more impactful than windows and glazing. In this first in a series on window selection, we’ll take a look at glare - how to understand what causes it and strategies for reducing and/or mitigating it.
For daylighting that is balanced and comfortable, it’s important to avoid glare. Our eyes adjust to brightness but aren’t as comfortable with high contrast in one space. Avoid contrasting light levels greater than 1:10, and even 1:3 depending on task.
For example, a room with a large south-facing window could easily get up to 300 foot-candles of light on that side of the room, so be sure the other areas of the room achieve 30-60 fc. For a work space, target perhaps 100 fc at the brightest and 30 for darkest areas. A few strategies:
Modeling: Consider daylight modeling to help determine light levels and potential for glare.
Light on Two Sides: Use strategically placed windows or skylights on opposite sides of the space. Big beautiful window? Consider adding a suntube or clerestory at the opposite end of the room.
Adjust Visible Light Transmittance (Tvis): In a recent project, the architect selected large windows for views and the particular aesthetic style, but the quantity of daylight on the one wall was so high that glare would have been uncomfortable. Tvis is the measure of how much light is let through the window vs. reflected back out. For small windows, we usually want a high Tvis to optimize the daylight, but in this case, we needed to turn-down the light levels. The daylight study below shows light levels at three times throughout the day, the first with a Tvis of 50% (pretty typical of clear windows) and the second with a Tvis of 30% for more even – and comfortable – light levels.
Focused Window Area: If there is only one available wall, consider reducing window area, focusing on a key view rather a broad swatch of daylight.
Electric Lighting: Another option is designing high efficiency electric lighting on an opposite wall, such as an LED wall wash or uplighting from above a cabinet.
With attention to detail, the right windows can improve energy efficiency, cost and comfort while allowing the beauty of the design to shine through.
Interested in Daylight Modeling for your next project? Contact us!