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).

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).

Figure 1 – Daylighting strategies incorporated into Atrium II, an office building in Secaucus, NJ. (Source: Rutgers Center for Green Building)

How to Implement Daylighting

Designing for daylighting in existing buildings involves complex interactions among multiple building systems and disciplines, requiring an integrated design process. Renovations provide an opportunity to assess current daylight levels and identify opportunities for improvement.

The first step to a daylighting and lighting upgrade is to conduct a lighting audit or survey that establishes information about all the lighting technologies and consumption patterns in a building.  Use Energy Star Portfolio Manager to benchmark energy usage and identify lighting upgrade opportunities.

The following steps outline strategies to integrate daylighting and electrical lighting into lighting upgrade projects.^[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.

While daylighting strategies, such as maximizing southern building orientation, may not be technically or financially feasible for a renovation project, many daylighting strategies are available for existing buildings, including:^[8]

• Opening the building perimeter to office space.
• Transferring light through perimeter spaces through lower partitions or by replacing opaque panels with transparent or translucent panels.^[9]
• Exposing closed-off overhead glazing.
• Creating light shelves for high spaces.
• Adding skylights, clerestories, atria, or roof monitors.
• Improving reflectance values for ceiling tiles, walls, and carpet.^[10]

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.^[11]

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.

For daylighting strategies specific to existing commercial projects, see Guide 5 of the Philadelphia High-Performance Building Renovation Guidelines.

Examples

Atrium II, Secaucus, NJ

Renovations to Atrium II, a 260,000 square foot office building in Secaucus, NJ, included improved daylighting through upgrades to the building envelope and the installation of lighting controls such as timers, photocells, and motion sensors.

Perimeter Office Zones, Washington, DC

This case study and design guide examine the best combination of window area, shading device and glazing type to save energy.

Benefits

Controlled, natural lighting can lead to many improvements:

• Reduced operating costs through reductions in electrical lighting usage.^[12]
• Reduced cooling loads and downsized HVAC systems through less heat gain from electrical lighting (see Properly-Sized, High-Efficiency HVAC and Controls).^[13]
• Improved employee productivity and satisfaction based on a shared preference for naturally daylit spaces, reinforcement of circadian rhythms, and connection to nature.^[14]
• Above average lease rates and lower tenant turnover.^[15]

Costs

The cost associated with integrating daylighting strategies into an existing building varies depending on the scope of the project. The design and material selected for interior or exterior shading and solar control devices, for example, impacts the cost. There is a range of options available from very low-cost solutions such as rearranging the layout of a room to a more comprehensive approach of adding integrated lighting controls and shading devices. 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 continues to provide interior light to building 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] 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] Philadelphia High-Performance Building Renovation Guidelines. www.phila.gov/pdfs/PhiladelphiaGreenGuidelines.pdf (accessed April 4, 2018).

^[9] California Energy Commission (CEC) and Heschong Mahone Group. 2013 “Office Daylighting Potential”

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

^[10] Ibid. CEC and Heschong Mahone Group.

^[11] WBDG. Daylighting. http://www.wbdg.org/resources/daylighting.php (accessed April 4, 2018).

^[12] Ibid WBDG.

^[13] Efficient Windows Collaborative. 2018. Daylight Controls. Windows for High-Performance Buildings. http://www.commercialwindows.org/daycontrols.php (accessed July 5, 2018).

^[14] California Energy Commission and Heschong Mahone Group. 2013 “Office Daylighting Potential”

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

^[15] Daylight Dividends, Rensselaer Polytechnic Institute. “Daylighting Resources – Productivity.” http://www.lrc.rpi.edu/programs/daylighting/dr_productivity.asp (accessed April 4, 2018).