Daylighting

What is Daylighting?

Daylighting combines building orientation, fenestration (e.g., the location of windows and openings in a building), shading devices, interior design, and lighting and controls.  Daylighting design illuminates indoor spaces with appropriate levels of natural light, minimizes glare and heat gain, and reduces electrical lighting needs (see Integrated Design Process, Building Orientation, High-Efficiency Lighting Systems and Networked Lighting Controls, Glare and Heat Gain Reduction and Sensor Controls).

Building orientation, in combination with window selection and placement, impacts daylighting levels, thermal comfort, ventilation, and views to nature (see Natural Ventilation and Energy Efficient Windows). A daylighting-optimized building maximizes south and north exposures and minimizes east and west exposures. Low sun angles make it more difficult to shade and to avoid glare and heat gain from east and west facing windows compared to south and north facing windows that receive direct and indirect natural light, respectively.^[1] The design and choice of window glazing affect the amount, distribution, and quality of daylight.^[2] For example, glazing systems with tinted glass and low-solar low-E coatings reduce solar heat gain with little reduction in visible transmittance or the amount of light in the visible portion of the spectrum.^[3] Skylights, solar tubes, clerestory windows, and cupolas can also help introduce and balance daylight in a room. Utilize the upper portion of windows to introduce high levels of daylight and avoid glare issues, while taking advantage of views from the lower portion of windows, balanced by proper shading.^[4] Exterior shading and control devices such as light shelves, overhangs, awnings, and self-shading elements of building form such as wings and deep-set windows can reduce heat gains, soften harsh light contrasts, and diffuse natural light. Interior designs that incorporate open layouts and light-colored surfaces also help distribute natural light. Reduce electrical lighting consumption and costs, and associated waste heat by pairing harvested daylight with automated dimmers and photosensors (see High-Efficiency Lighting Systems and Networked Lighting Controls).

How to Implement Daylighting

Designing for daylighting involves complex interactions among multiple building systems and disciplines, requiring an integrated design process. For example, window glazing influences interior electrical lighting design, sizing of mechanical systems, and interior design layouts. The following outlines steps to integrate daylighting and electrical lighting.^[5]

1. Set a Maximum Lighting Power Density (LPD) goal to avoid overlit spaces and to achieve an appropriate level of lighting per area lit or watts per square foot.
2. Set a Daylight Sufficiency Goal that establishes the amount of daylighting, measured in lumens or foot-candles, required to perform a typical task in each space without electrical lighting.
3. Develop a layered lighting strategy that first utilizes daylight to provide basic or ambient lighting levels, and then adds electrical lighting options and controls to vary lighting levels for a variety of tasks and occupant preferences.

Daylighting guidelines provide general principles and examples, but project specific solutions often require hiring a daylighting expert familiar with advanced computer simulation software and tools, which can effectively simulate a range of scenarios and outcomes.^[6]

The Facade Design Tool by the Efficient Windows Collaborative compares several design parameters including orientation, window area, controls, shading, and window type to predict performance outcomes such as annual energy use and savings, daylight levels, glare, and thermal comfort.

Low Energy – High Performance:  Building Façade Solutions by Berkeley Lab offers a list of simulation software for modeling window system performance.

Benefits

• Improved life-cycle cost, reduced emissions, and reduced operating costs through reductions in electrical lighting usage.
• Reduced operating costs through reductions in electrical lighting usage.^[7]
• Reduced cooling loads and downsized HVAC systems through less heat gain from electrical lighting (see Properly-Sized HVAC Equipment).^[8]
• Improved occupant satisfaction and comfort based on a shared preference for naturally daylit spaces, reinforcement of circadian rhythms, and connection to nature.^[9]

Costs

Planning for daylighting should be integral to the design process and should not impose a significant impact on project costs if considered from the early stages of design. Windows with more than one pane and glazing to control temperature fluctuations and reduce UV exposure tend to cost more than conventional windows. Increasing the window to wall ratio to promote natural daylighting cost more than the construction of standard walls. The average national cost of window installation is $5,040, with most homeowners spending between $2,584 and $7,497 depending on materials, features, and size.^[10] Structures such as a copula require more materials and are more technically challenging to build and incur additional costs.  Additional upfront costs associated with daylighting strategies or hiring a daylighting consultant typically pay for themselves through electrical lighting reductions and associated energy cost savings.

Resiliency

In the event of a power outage, a daylighting-optimized home continues to provide interior light to occupants, while at the same time reducing reliance and stress on the grid and providing energy savings.

^[1] Lawrence Berkeley Laboratory and US DOE. 2013. The Integrated Approach: Tips for Daylighting with Windows. Page 32. https://facades.lbl.gov/sites/all/files/tips-for-daylighting-2013.pdf (accessed July 6, 2018).

^[2] Efficient Windows Collaborative. 2018. Daylighting. http://www.commercialwindows.org/daylight.php (accessed July 6, 2018).

^[3] Efficient Windows Collaborative. 2018. Window Technologies: Transmittance. http://www.commercialwindows.org/transmittance.php (accessed July 6, 2018).

^[4] General Service Administration (GSA) Office of Federal High-Performance Green Buildings. 2018. “Saving Energy Through Lighting and Daylighting Strategies.” https://www.gsa.gov/cdnstatic/Lighting_and_Daylighting_Two_Pager_508_compliant_2-9-15.pdf (accessed Dec 11, 2018).

^[5] General Service Administration (GSA) Office of Federal High-Performance Green Buildings. 2018. “Saving Energy Through Lighting and Daylighting Strategies.” https://www.gsa.gov/cdnstatic/Lighting_and_Daylighting_Two_Pager_508_compliant_2-9-15.pdf (accessed Dec 11, 2018).

^[6] WBDG. Daylighting. http://www.wbdg.org/resources/daylighting.php (accessed April 4, 2018).

^[7] Ibid WBDG.

^[8] Efficient Windows Collaborative. 2018. Daylight Controls. Windows for High-Performance Buildings. http://www.commercialwindows.org/daycontrols.php (accessed July 5, 2018).

^[9] California Energy Commission and Heschong Mahone Group. 2013 “Office Daylighting Potential” http://www.sunlightindoors.com/resources/SunlightBenefits/OfficeDaylightPotential.pdf (accessed April 5, 2018).

^[10] HomeAdvisor – True Cost Guide – Installing Windows https://www.homeadvisor.com/cost/doors-and-windows/install-windows/ (accessed April 6, 2018).