Happy Autumn Equinox!

Did you know Autumn Equinox is the day most modeling programs want to measure daylight?  And Here are 5 Other Things You May Not Know About Daylight in Buildings.


Windows account for only a portion of a building’s design, but architects go to great lengths to ensure exposure to daylight is maximized (Why? Just keep reading). Where should the windows go? How big should they be? How many? These are all questions architects ask when designing a building in cooperation with budgets, planning, and other space and materials requirements.


Morgan St U CBEIS seminar rooms

(Abundant natural light in a classroom at the Morgan State University Center for the Built Environment and Infrastructure Studies.)

Basically…it’s hard work.  Here are five things you probably didn’t know about daylight.

1.   Glazing isn’t just for cakes.

 Architects often refer to windows as glazing.  There are certain characteristics of glazing that architects specify such as the “U-Value,” “Solar Heat Gain Coefficient” and the “Visible Light Transmittance,” or VLT.  While the first two are extremely important for controlling heat gain and energy transfer through the windows, the VLT is what matters most for the amount of daylight entering your building.

2.  There are several different design standards for daylight and also several different ways to comply.

If you’re entrenched in the architecture or sustainability world, chances are you’re familiar with LEED (Leadership in Energy and Environmental Design). It’s been the go-to standard for green buildings since it was unveiled in 2000. But LEED has changed over the years (we are now up to version 4!) and LEED is not the only green standard out there. You may have heard of the International Green Construction Code (IgCC,) or the WELL Building Standard – both of which also talk about Daylight but with different specific requirements.



To figure out how much daylight is in your building, there are three paths – you can calculate, model, or measure.  But beware – not all standards accept all the different paths.  For example, LEED v4 and the WELL standard do not allow calculations.  Also, as shown in the chart here, the specific standards for modeling daylight, shown in the unit of “Foot-candle,” differ with each standard.

3.  A Foot-Candle?

Daylight is modeled and measured in the unit of foot-candles (fc) or lux.  While some may think of this as a sophisticated unit of measure – it really is the most basic. One fc is the amount of light reaching a 1-foot x 1-foot square one foot away from one candle.  Some standards reference lux, which is just the metric version of fc – so one lux is the amount of light of 1 candle that falls on a 1-meter x 1-meter square that is one meter away. (You can convert one to the other using this equation:1 footcandle = 10.7639 lux!)













4. There are a ton of software programs to model daylight.

So how do we choose – and are there any programs that architects already use that can do this?

  • Revit is a BIM (Building Information Modeling) program that architects use for Construction Documents. There is a plug in within Revit to analyze daylight –preset to model against only the LEED v3 and v4 standards.
  • 3D Studio Max (3DS) is a program architects often used for renderings. 3DS has a “Lighting Analysis Assistant” – which has no preset standard, meaning the modeler can analyze all of the data based on each standard’s minimum and maximum levels.
  • Trane TRACE 700 is a program that an engineer may be using for the building’s energy model. It also has a “Daylight Module” but this program is better used to predict the energy savings from daylight – rather then what is needed to comply with the standards.


 5.  Daylight is more important than you might think.

 You may be thinking, “Why do we care so much about sunshine?” Simply put: Because it’s really, really important.

The quality of daylight distribution has a direct impact on the health and wellness of the people who live and work within a building. For example, many studies have shown that students who study in day-lit classrooms demonstrate better work habits, improved academic performance, and are less likely to feel tired than students in classrooms lit solely by artificial lighting.

But it’s not just students who benefit from daylight. We all need natural lighting because sunlight regulates our circadian rhythm – and improving your circadian rhythm has dramatically positive effects on your body and your mood. Not to mention improved visibility and vitamin D production. Important? We think so. Because at the end of the day, designing buildings that help people live better and be better is what we’re all about.



Credit for above image:

Want to know more? Click here for “Design Tools for Daylight”- a comparative research analysis of the daylight tools available to designers.



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