Low Energy Facades & Daylighting

Low Energy Facades & Daylighting

indows Pioneers: Charlie Curcija, Steve Selkowitz and Eleanor Lee
Windows Pioneers: Charlie Curcija, Steve Selkowitz and Eleanor Lee


New fenestration technologies and systems that optimize the synergies between the façade, lighting, and mechanical systems can deliver high performance throughout a building's lifespan. These "integrated" solutions represent a key opportunity to significantly reduce energy and demand, helping to move us toward our goal of zero net energy buildings by 2030.

Daylight Systems

The challenge of daylighting buildings has been about how to achieve an efficient redistribution of flux within a building with a source that is both variable in intensity and position: the sun and the sky. Solving this problem will reduce or eliminate the need for electric lighting during the day.

Energy savings are achieved through daylight-controllable lighting systems, but interior shades can reduce daylighting potential, and glare poses significant challenges. If a low-cost technology can be devised for widespread applications, daylighting has the potential to reduce U.S. energy use by 1.0-1.5 quads (1.0-1.5 x 1015BTUs). Berkeley Lab researchers are working to develop new materials and systems for daylighting buildings in collaboration with industry.

Daylight Systems Technologies

Measuring Optically Complex Fenestration Systems 

Measuring light-scattering materials systems

Most daylighting and shading systems are “optically complex” in that incident light is not transmitted specularly (in the same direction as the incident light) like transparent glass. Light is scattered: transmitting in some directions and reflecting in others; the pattern of scattering differs as the angle of incident light changes. LBNL researchers are establishing protocols for measuring and characterizing the light-scattering properties of these systems.

Modeling Daylight 

Modeling daylighting systems for building applications

Evaluating the annual energy performance of daylighting systems used to take days and even weeks for a single point-in-time calculation. LBNL researchers are developing and validating the time-efficient simulation tools (i.e., Radiance, EnergyPlus) needed to evaluate the annual daylighting and window heat gain (and therefore, total energy use) impacts of fenestration systems, including more recent optically complex fenestration systems (CFS).

Virtual Prototyping

Radiance software and cloud computing to speed innovation

The ability to characterize the daylighting performance of an optically complex fenestration system (CFS) by simulation and to quickly simulate annual performance facilitates iterative design and optimization. LBNL’s GenOpt can be paired with Radiance and the new Radiance CFS capabilities to computationally derive optimal CFS designs. This modeling capability can significantly reduce the cost of early-stage R&D, enabling simultaneous development of prototypes and assessment of energy-savings potential for informed business decision making. This capability was applied to derive more optimal designs for microprismatic daylighting films.

Prismatic Window Films

Sunlight redirection with an indoor window film

Prismatic window films are made through embossing, with surface textures of depths between 10 nanometers up to 200 microns. They are manufactured in a cleanroom environment via roll-to-roll processes with widths that are applicable to large-area windows (e.g., 2 meters). LBNL researchers collaborate with industry to develop, characterize, simulate, and field test new materials that have the potential to displace lighting energy use up to 40 feet from the window.

Dynamic Metamaterials

Nanoscaled prismatic structures that shape-shift with applied voltage

Switchable daylight-redirecting structures can be fabricated from electro-responsive polymers by nano-imprinting or nano-hot embossing methods that are applicable to large areas and fine-feature resolution and are compatible with low-cost in-line industrial manufacturing processes. If dynamic glazings based on electro-actuated optical metamaterials can be developed, daylight redirection and diffraction efficiency could be externally modulated, thereby optimizing lighting energy savings over a larger fraction of building floor space.  In a collaborative project between the LBNL Material Science Division and LBNL Windows researchers, material science R&D was guided by detailed energy and comfort analysis of hypothetical prototype technologies.

Optical Light Shelves

Passive optical louvers for daylighting deep spaces

A passive optical light shelf relies on reflective materials and engineered profiles to redirect incident sunlight uniformly onto the ceiling and typically requires no adjustment over the year. The systems are designed to be installed in the upper clerestory portion of the window and must control specular sunlight and surface brightness to avoid glare. In some instances, the same system can be coupled with a plenum-installed light pipe or skylight for greater efficiency in core spaces. Research has been conducted to develop new designs and evaluate commercially-available daylight-redirecting technologies.

Multi-zone Daylighting + Shading Systems

Indoor and outdoor shading with an upper zone for daylighting

Zoning or assigning unique functions to specific areas of the window wall is a common approach to enhancing daylight and controlling glare. The lower window permits a view out and is controlled by the occupant, while the upper window is reserved for daylight admission. Zoned, interior venetian blind systems can provide such functions. The lowest-cost solution is a conventional blind where the slat angles of the upper and lower sections differ and are ganged to move together (dependent relationship). A variant of this is to use two separately mounted blinds so the slats can be controlled independently. LBNL conducted field tests of these types of systems to evaluate energy performance and impacts on visual comfort.

Diffusing Materials

Diffuse daylight from windows and skylights

Traditionally, light-diffusing materials have been used in skylights and sloped glazing to daylight interiors. Diffusing or translucent glass or panels placed in the clerestory portion of the window wall can transmit daylight in a diffuse, non-directional pattern to supplement daylight from the lower view window. For some commercial systems, the conductance of the panel is decreased with the use of an insulating infill material such as aerogels or polymer strands. Field studies have been conducted to evaluate the performance of these systems under real sun and sky conditions.

Holographic Glazings

Diffractive gratings for daylighting

The diffractive properties of holographic structures present an opportunity to improve the daylight performance in side-lit office spaces by redirecting sunlight to the ceiling plane. LBNL has characterized several prototype holographic structures using tabletop goniophotometric measurements, then conducted simulations to evaluate energy performance.

Spectrally Selective Low-e Glazing and Films

Clear glass without the solar heat gains

Spectrally selective low-emittance coatings transmit visible wavelengths while reflecting the near infrared. The result is a glass with a clear appearance that admits more daylight and provides solar control, replacing the conventional bronze tinted or reflective solar glazings that produced gloomy indoor environments. High-performance, low-emittance coatings continue to be developed by industry to improve solar-optical performance and durability.


Daylighting building interiors with toplighting

Skylights and sloped glazing can lower energy requirements for both space conditioning and lighting if the size, spacing, and properties of the skylights are properly specified. LBNL has conducted research to characterize and improve the daylighting and thermal performance of skylights using parametric simulations, calorimeter tests, and field demonstrations.

Integration with Daylighting Controls

Improving the reliability of photoelectric dimming control systems

Electric lighting systems can be switched or dimmed in proportion to available daylight to reduce annual energy use and peak electric demand in sidelit perimeter zones or skylit core zones. Historically, these daylighting control systems have had a poor reputation for responsiveness and reliability, and to this day, this reputation continues. One critical challenge is how to obtain proper proportional dimming using a ceiling-mounted photosensor when the relationship between the photosensor and the desired work plane illuminance is non-linear. LBNL researchers have characterized this behavior using field tests and developed modeling tools that enable more comprehensive detailed studies to be conducted.

Visual Comfort and IEQ

Evaluating comfort and indoor environmental quality impacts of daylighting systems

Discomfort glare, perceptions of interior brightness or gloom, and access and quality of outdoor view are all performance metrics used to evaluate window and daylighting systems. If the technology alone is incapable of delivering comfort on a routine basis, occupants will intervene, which in turn can reduce its effectiveness. LBNL has conducted research to develop both the tools for evaluating visual discomfort and to derive metrics for the evaluation of daylighting impacts.

IEA SHC Task 31

The International Energy Agency's Solar Heating and Cooling Programme's task to daylight buildings in the 21st century (focus on tools and occupant impacts)

The objective of the Solar Heating and Cooling (SHC) Programme of the International Energy Agency (IEA) under IEA Task 31 was to make daylighting the typical and preferred design solution for lighting buildings in the twenty-first century by integrating human response with the application of daylighting systems and shading and electric light control strategies. LBNL collaborated with researchers world-wide to develop guidance and tools for promoting the use of daylight in buildings.

IEA SHC Task 21

The International Energy Agency's Solar Heating and Cooling Programme's task to daylight buildings in the 21st century (focus on technologies)

The Solar Heating and Cooling (SHC) Programme of the International Energy Agency (IEA) under IEA Task 21, Energy Conservation in Buildings & Community Systems, Programme Annex 29 was a five-year international collaboration to advance daylighting technologies and promote daylight-conscious building design. A source book was one result of this coordinated effort to gather the most up-to-date information available about the application and evaluation of advanced daylighting systems. The book emphasizes the performance of daylighting systems and includes a survey of architectural solutions, which addresses both conventional and innovative systems, as well as their integration in building design.

Related Facilities
  • Solar Optical Properties Laboratory
  • Full-scale Testbeds
  • Spectrometer
  • Spectro-goniometer
  • Large Diameter Integrating Sphere
  • Advanced Windows Testbed Facility
  • Field Measurements
  • Facility for Low Energy Experiments in Buildings (FLEXLAB)
  • Rapid Prototyping

Explore the Facilities page. 

Switchable Glazings

Switchable windows — 'smart' windows that can adjust dynamically with changing weather and building conditions — offer a way to minimize lighting and HVAC energy use, minimize peak energy loads that can affect demands on the micro- or utility grid, and address the demands of occupants in real time. The challenge has been to craft low-cost switchable windows that can last 30-50 years.  

Advances in material science have resulted in the development of durable large-area switchable coatings on glass, or films that passively vary with incident light or heat or can be modulated at whim, either manually or automatically. Material science continues to improve device properties and durability. Berkeley Lab has been investigating the design, control, energy performance, and occupant impacts of switchable windows in commercial and residential buildings over the past two decades.

Related Facilities

Related Research Facilities

  • Solar Optical Properties Laboratory
  • Spectrometer

Explore the Facilities page. 

Intelligent Dynamic Façades

While static window technologies provide practical low-cost technological options to manage both space conditioning and lighting energy use, automated fenestration systems offer the potential for greater, more optimized total energy savings in response to variable conditions. 

With this in mind, the future design of high-performance buildings is expected to involve active façade technologies, acting in intelligent collaboration with HVAC and lighting systems to produce comfortable indoor environments with reduced energy consumption. In collaboration with industry, LBNL researchers are working to develop, test, and increase market adoption of innovative, intelligent dynamic façade systems.

Intelligent Dynamic Façades Technologies

Motorized Shades

Motorized venetian blinds, louvers, roller shades, and awnings

Automated, motorized shading has been commercially available for decades. Most products are designed to block direct sun either through the height of a roller shade or the slat angle of a louvered system. More recently, products have begun to tackle glare, exterior obstructions, integration with other building systems, and fault detection and diagnostics to improve end-user satisfaction and facilitate operation and maintenance. LBNL has conducted research in collaboration with industry to understand the performance impacts of automated systems on energy use, peak demand, and most important, end user comfort, satisfaction, and acceptance of automated shading.

Switchable Windows

Switchable coatings on glass or films that modulate daylight and solar heat transmission

See our section on Switchable Windows on this page. 

Model Predictive Controls

Multi-parameter control for more optimized performance

Model predictive controls (MPC) can yield significant reductions in energy use and peak demand, enable greater responsiveness and stability of the utility grid as alternative renewable energy sources come on line, and improve occupant comfort and the indoor environmental quality of buildings. It is a common control technique in other fields, particularly in the chemical, automotive, and aerospace industries, and has been shown to be potentially beneficial for many aspects of building controls.

The central idea of model predictive control is that a model of the system is repetitively interrogated to determine the best control strategy given some particular set of weather conditions and other sensor readings or other building or occupant-related information, potentially including weather forecasts. LBNL research and development is focused on developing and evaluating low-cost methods of producing controllers that approximate MPC. A field testbed environment has been established that enables real-time co-simulation and testing of prototype systems under real sun and sky conditions.

Occupant Behavior

End-user comfort, satisfaction, and acceptance of automated façade systems

Market adoption of automated façade systems is critically dependent on how well occupants accept the systems and whether they are satisfied and comfortable with the resultant indoor environment. End-user acceptance is in part dependent on the properties of the device, such as: how quickly the system responds to conditions of discomfort, how well it can mitigate sources of discomfort, and the quality of the indoor environment when the system is deployed. Acceptance is also critically dependent on how the system is actuated: if inadequate, the system will be disabled, and the anticipated benefits will not be obtained. LBNL has conducted research to better understand end-user behavior and its impact on projected energy performance.


Monitored case studies of buildings using intelligent façade systems

Demonstrations provide the critical third-party performance data for pre-commercial, emerging technologies in real occupied buildings, helping to speed market adoption by lowering the risk of innovation. LBNL researchers work with industry partners, building owners, and architects and engineers to develop procurement specifications, understand installation methods, develop commissioning guidelines, and evaluate impacts on building operation and maintenance. Monitored energy performance data and subjective surveys are used to determine energy and occupant impacts and improve performance, when possible.

Related Facilities

Related Research Facilities

  • Solar Optical Properties Laboratory
  • Spectrometer
  • Advanced Windows Testbed Facility

Explore the Facilities page. 

Angular selective systems

Angular Selective Systems 

Static angular selective shading systems block direct sunlight and admit daylight within a specific range of incident solar angles.

Berkeley Lab researchers work to harness this potential to reduce energy use and peak demand in commercial buildings using state-of-the art whole-building computer simulation software that allows accurate modeling of the behavior of optically-complex fenestration systems such as angular selective systems. 

Ventilating Facades

Ventilating Façades

A ventilated facade is a cladding system with an air cushion or cavity immediately behind which provides with a drainage, ventilation and thermal solution.

Our research focuses on utilizing this technique in building design to provide the optimal energy-efficiency and cost savings for building owners, while ensuring the comfort and safety of building occupants.