Frequently Asked Queestions - Daylight Modeling
Daylight Modeling/Simulation
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Frequently Asked Questions


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What is daylight?
What is daylighting?
What is daylight modeling?
What is daylight modeling used for?
What information can I expect on a daylight modeling report?
How is daylight measured?
What software do you use?
How do I know what amount of daylight is appropriate for my project?
Do you offer LEED Credit 8.1 documentation?
Can you model glass?
Should I be concerned about solar heat gain?
Does daylighting let in too much heat?
What are the health benefits of daylight?
Do you offer accredited presentations?
Where can I find more information about daylight and daylight modeling?


What is daylight?

Daylight is controlled natural light, from the visible the part of the solar electromagnetic spectrum between 380 and 780 nm. Daylight is not direct sunlight.

Wavelength

Wavelength (nanometers)

What is daylighting?

Daylighting is the practice of using controlled natural light to illuminate a space. By starting with the concept of using the building itself as a luminaire, efficient daylight design reduces the need for artificial/electric lighting, supplemental HVAC and improves the environment within for the occupants, both mentally & physically. There are many ways to manage sunlight, including use of diffusing and light reducing fenestration materials, as well as employing design techniques such as light wells and solar shading devices.

What is daylight modeling?

Daylight modeling is a software or physical scale model calculation of interior light levels in a space, using specific sky scenarios, such as clear sky or overcast, or real world weather data files for a specific location. For the purposes of this web site, we are referring to software simulation. The building is built within software, and design options can be tested early in design phase. For accurate simulation results, several factors should be taken into consideration, such as the building orientation, location, local climate data, and interior finishes, which all impact the amount of available daylight for a specific project. Results can be displayed through a false color grid and renderings. After an initial analysis, the building model can then be modified to reflect options that may improve the daylight design, such as changing glazing location or light transmittance.

What is daylight modeling used for?

Daylight modeling may be used to:
  • Compare different design options
  • Verify that a proposed design will provide adequate daylight
  • Predict sources of potential glare, look at contrast ratios or balance of daylight within a space
  • Indicate potential energy savings from electric lighting use
  • Document daylighting code compliance

What information can I expect on a daylight modeling report?

See an example of a Daylight Modeling Report.

How is daylight measured?

Daylight can be measured in a number of different ways. We use Radiance to show illuminance and luminance for static analysis, ie. looking at light levels at a particular point in time. For dynamic analysis we use daylight autonomy.

Illuminance = The amount of luminous flux (quantity of light emitted by a source) that falls on a surface. Illuminance is measured in lux (lumens per meter squared) or footcandles (lumens per foot squared) 1 fc = 10.76 lux

Luminance = The luminous intensity (power emitting by a light source or reflected from a surface in a given direction) that is received by the human eye. It is based on a specific direction and is used to detect glare. Luminance is measured in candelas per meters squared (cd/m2). This measurement also helps understand whether GLARE might be an issue in a project design.

Daylight Autonomy = The percent of occupied times of the year for which the minimum illuminance requirement is met by daylight alone. Target illuminance levels guidelines by space type and task type are available from the Illuminating Engineering Society for North America, and the CIE. Daylight autonomy software imports historical data sets of solar radiation and meteorological elements, leading to an analysis that considers all sky conditions throughout the year for the specified location.

What software do you use?

We build most of our daylight models in Ecotect. Then the model is exported to Radiance and/or DAYSIM for analysis. Radiance and DAYSIM are both validated software packages. These programs can be used to generate several forms of daylight analysis. View examples of Daylight Modeling Reports. Other software packages we may use include Rhinoceros, DIVA and Grasshopper.

How do I know what amount of daylight is appropriate for my project?

The amount of daylight required varies with the specific task(s) being performed in the space and the age of the occupants. There are several creditable organizations that make light level recommendations. Some of those organizations are:

Illuminating Engineering Society of North America
International Commission on Illumination (CIE)
U.S. Green Building Council

Do you offer LEED Credit 8.1 documentation?

Yes, we can assist you with documenting LEED IEQ Credit 8.1 - Daylight & Views. Visit the US Green Building Council website for the current requirements of this LEED credit.

Can you model glass?

Yes, we can include glass in the daylight model. To do so, we will need to be provided with the visible light transmittance of the glass.

Should I be concerned about solar heat gain?

Yes. Failure to contemplate the effects of solar heat gain can have a negative impact on both the occupants and the cooling system. With proper knowledge and planning, the appropriate materials can be selected and uncomfortable conditions can be avoided.

Does daylighting let in too much heat?

The light-to-heat ratio for daylighting is better than even the most efficient electric lights. Well designed, daylit spaces reduce the need for electric lighting, supplemental cooling and result in both energy savings and a reduction in heat gain.

What are the health benefits of daylight?

Studies have shown there are many health benefits associated with natural light. These include, but are not limited to:
  • Improved mood and energy
  • Increased productivity
  • Reduction in eye strain
  • Higher academic performance
  • Stimulation and regulation of the nervous and endocrine systems
  • Increased safety
  • Decreased stress levels
  • Improved patient recovery in health care facilities
Although sometimes overlooked in building design, the physiological and psychological benefits of natural light are important considerations.

Do you offer accredited presentations?

Yes. Kalwall Corporation offers an AIA Continuing Education System (CES) presentation that includes daylighting learning objectives. It provides 1 Learning Unit Contact Hour in Sustainable Design and Health Safety and Welfare. To learn more about scheduling these presentations, please contact info@kalwall.com.

Where can I find more information about daylight and daylight modeling?

Kalwall Corporation   www.kalwall.com
IES - Illuminating Engineering Society   www.iesna.org
CIE - International Commission on Illumination   www.cie.co.at
Radiance   www.radsite.lbl.gov/radiance/
DAYSIM   www.daysim.com
EnergyPlus Energy Simulation Software - Weather Data
    www.apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm
US Green Building Council - LEED    www.usgbc.org/DisplayPage.aspx?CategoryID=19
Daylighting Collaborative   www.daylighting.org
NCEF - National Clearinghouse For Educational Facilities   www.ncef.org/

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