Resources Since the 1970s, Lawrence Berkeley National Laboratories (LBNL) Windows and Daylighting group has been leading the field with innovations in research, product concepts, design assistance, and software. Those interested in working at a detailed level with glazing systems should consider becoming familiar with lab’s numerous publications and software provisions. Start by downloading Window 5.2 (current version) and Optic 5.1 (current version) from the LBNL website, www.windows.lbl.gov. To support these important software systems, LBNL also maintains a database for a wide range of products, including windows, assemblies, coatings, and films, allowing complete analysis of glazing assemblies for their thermal as well as optical qualities.
Daylighting: The Once and Future King As we start designing more daylighting into buildings, many of the 20th century’s bad habits, such as overglazing and careless glazing orientation, will creep into designs. The tendency to favor style and view over solar concerns will continue to challenge architects and lighting designers, but going forward we must have better solutions and creative alternatives. Mastering the ability to address the many principles and side effects of glazing is new to most of us, but it can’t be for long.
In part two, (Sept/Oct 2007), the many alternatives to regular windows and skylights will be explored, including a wide range of concepts from distorting and diffusing panels to refracting and embedded optics.
When Daylight Isn’T Itself Daylight is the perfect-color light source. Even though the color temperature changes due to weather, time of day, and time of year, for all practical purposes the color rendering index (CRI) of daylight is 100, and color evaluations are often best made outdoors. With single-pane clear window glass, the CRI may drop a little (98+), but overall the color quality is close to perfect. However, when using multilayer glazing assemblies—and especially with tinted and lowE glass—daylight is altered. Here are a couple of interesting examples.
Pink Lights In an office building with dark-green tinted glass, electric lights in the core areas were described as “pink” even though they were actually modern 3500K T8 lamps. Upon inspection, workers in office areas near the windows had become adapted to green daylight with a CRI of about 55, worse than old-fashioned “cool white” fluorescent. When they left the area and entered the core of the building, they experienced transient color adaptation, which occurs when a viewer who is fully adapted to viewing a saturated color of light (green) will, upon entering a white light environment, see objects tinted to the color wheel opposite (magenta) until readapted to white light. Nothing could be done about it.
Daylighting for a Dental Clinic Housed in a modern medical office building with dark-bronze tinted glass, dentists and dental technicians complained about the color of daylight, which is important in the matching of crowns and cosmetic dental work. The approximate CRI of the filtered daylight was determined to be about 68 with a distinct greenish-brown tint. Although some energy efficiency was lost, the glass was replaced with clear glass, and the problem was solved.