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 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).

Figure 1 – Sunshade at Rutgers Visitor Center (Source: Rutgers University).

Building orientation, in combination with window selection and placement and reflection and glare from adjacent buildings, impacts daylighting levels, thermal comfort, ventilation, and views to nature (see Natural Ventilation and Views and Operable 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 more favorable sources of direct and indirect natural light, respectively.^[1] The design and choice of window glazing also 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] Introducing daylight from skylights or solar tubes can also help 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, louvers, and reflecting systems 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 bounce light throughout interior spaces. For example, dark interior finishes can compromise an otherwise successful daylighting design.^[5] Furniture, cubicles, and workstations can block light and have a substantial impact on the light levels in a given space. Model any partition systems or permanent furniture in the design phase as they can have a significant impact on interior light levels.^[6] 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 into new commercial buildings.^[7]

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 that can effectively simulate a range of scenarios and outcomes.^[8]

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.

Examples

The Hoffmann-La Roche Ltd. Office Building, NJ

This building uses several design strategies to bring daylight into a massive central core building including small interior atriums, light shelves, and prismatic glazing.

Perimeter Office Zones, Washington, DC

This case study and design guide examine combinations of window area, shading devices, and glazing types to maximize daylighting and save energy.

Benefits

Controlled, natural lighting provides multiple benefits:

• Reduced operating costs through reductions in electrical lighting usage.^[9]
• Reduced cooling loads and downsized HVAC systems through less heat gain from electrical lighting (see Properly-Sized HVAC Equipment).^[10]
• Improved employee productivity and satisfaction based on a shared preference for naturally daylit spaces, reinforcement of circadian rhythms, and connection to nature.^[11]
• Above average lease rates and lower tenant turnover.^[12]

Costs

Daylighting design should not impose a significant impact to project costs if considered early in the design phase and integrated throughout the design process.  The costs of hiring an expert daylighting consultant and electrical lighting designer often pay for themselves through electrical lighting reductions and associated energy cost savings.

Resiliency

In the event of a power outage, a daylighting-optimized building provides interior light to building occupants, 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] US DOE. Lighting Design. https://www.energy.gov/energysaver/save-electricity-and-fuel/lighting-choices-save-you-money/lighting-design  (accessed September 10, 2018).

^[6] Whole Building Design Guide (WBDG) Daylighting. September 2016. https://www.wbdg.org/resources/daylighting (accessed September 10, 2018)

^[7] 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).

^[8] WBDG. Daylighting. http://www.wbdg.org/resources/daylighting.php (accessed April 4, 2018).

^[9] Ibid WBDG.

^[10] Efficient Windows Collaborative. 2018. Daylight Controls. Windows for High-Performance Buildings. http://www.commercialwindows.org/daycontrols.php (accessed July 5, 2018).

^[11] California Energy Commission and Heschong Mahone Group. 2013 “Office Daylighting Potential”

http://www.sunlightindoors.com/resources/SunlightBenefits/OfficeDaylightPotential.pdf (accessed April 5, 2018).

^[12] Daylight Dividends, Rensselaer Polytechnic Institute. “Daylighting Resources – Productivity.” http://www.lrc.rpi.edu/programs/daylighting/dr_productivity.asp (accessed April 4, 2018).