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Daylighting Design Aids and Tools

Analysis and simulation are important tools in daylighting design. You need both performance feedback and visual information to let you know how well the design functions in relation to your overall goals.

The terms analysis and simulation are often used interchangeably to describe the various methods and tools that aid in daylighting and energy efficient design. In general, analysis provides quantitative information (annual available natural light, thermal impacts of natural lighting, solar shading analysis, etc.). Simulation is used to create a qualitative visual interpretation of what the space may actually be like (renderings).

There are several tools and analysis methods available to help you assess your design. These include:

Simple tools and calculations
Physical modeling
Computer modeling

SIMPLE TOOLS AND CALCULATIONS

Simple tools and calculations are used in the most preliminary of design concept stages to help determine the viability of daylighting. With the advent of computer tools that are fairly easy to use, these simple methods are becoming obsolete.

Simple tools and calculations include:

Sunpath diagrams to calculate available daylight during different seasons at different latitudes
Daylight factor calculation for available interior daylight
Glazing factor calculation for available interior daylight
Fisheye photography for obstruction analysis

PHYSICAL MODELING

Physical modeling is exactly that—a physical to-scale model or full-scale mock-ups of your project to conduct daylighting availability analysis.

Advantages:

You are using real natural light
The subtle qualities of light are accurately demonstrated
Qualitative and quantitative information
Can represent any room geometry

Disadvantages:

Cannot control the sun or weather
Not easy to demonstrate design changes/iterations
Need to build the model
Local access to a heliodon or artificial sky
Difficult to create a model with the appropriate textures and reflectances
Difficult to mimic electric light sources
Does not provide information on thermal impacts of daylighting or potential energy savings

Physical model analysis methods include the use of the following as natural light sources:

Heliodon (model can be manipulated to mimic various latitudes and times of day)

Outdoor: use actual sky conditions and natural light to conduct analysis
Indoor: use artificial light sources to mimic natural light

Sky simulators (artificial sky)

Mirror box—overcast sky simulator. Reports results as daylight factors
Sky dome—can reproduce all types of skies
Spotlight sky simulator—can reproduce all types of skies
Scanning sky simulator

For more information on using these analysis techniques, visit the various daylighting lab websites. These labs offer analysis services but unfortunately are located in only a few areas in the country.

References:

Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000.

Overview of Daylight Simulation Tools / by Zack Rogers, PE, IESNA, LEED AP, Architectural Energy Corporation, LightLouver LLC, USA at the Daylight Symposium 2007.

Presentation by Barbara Erwine of Cascadia Conservation at the Daylighting Institute, LIGHTFAIR, 2004.

COMPUTER MODELING

Today, the trend is toward computer analysis to provide daylighting design information and feedback immediately to the design team. Historically, these tools were sufficiently complex that only researchers involved with product development and/or primary field research were able to use them. Today, however, there are many tools available that have varying levels of complexity in both input required and output obtained. There are free programs available as well as ones for purchase.

Advantages:

Parametric in nature - when you change one design element the resulting effects on other design elements are automatically changed
Some software provides three dimensional analysis
Can be easy to learn
Many programs have wizards to assist in model development

Disadvantages:

Some software can be costly
Often difficult to find team member capable of completing the modeling
Can be difficult to learn
Many programs have wizards to assist in model development (be warned - many wizards must be changed to accurately provide results for your project - ESPECIALLY if using software to evaluate thermal impacts of daylighting)

Depending on the goal of the analysis, software tools utilize different methods to achieve results and renderings. The categories of computer based tools are differentiated by the calculation methods they use:

Radiosity (see detailed description below)
Raytracing - backward and forward (see detailed description below)

Software Tools

This is not a comprehensive listing. If you would like information on a particular software tool, please contact us or refer to the resource links provided.

Autodesk Viz. This 3D visualization software has tools for modeling, animation, lighting, and rendering.
- Radiosity engine
- Performs solar shading analysis and glare/luminance ratios to some degree
- Strength is in solar animations, photorealistic animations and interior illumination Interoperable with AutoCAD applications
Developed by: Autodesk
Cost: Contact for pricing
ADELINE (Advanced daylight and electric lighting integrated new environment). ADELINE is an integrated lighting design computer tool developed by an international research team within the framework of the International Energy Agency (IEA) Solar Heating and Cooling Programme Task 12.
- Analyzes daylighting and electric lighting
- Provides 3-D CAD modeling of space
- Automatically generates Superlite and Radiance input files
- Calculates interior illuminance levels in complex spaces primarily for large commercial buildings
Developed by: Fraunhofer-Institute f�r Bauphysik
Cost: Contact for pricing
AGi32. This lighting analysis software program provides lighting calculations and renderings for electric lighting and daylighting system analysis.
- Powerful and fast
- Produces full-color renderings for daylighting and electric lighting analysis
- Easily creates and analyzes complex environments
- Includes comprehensive library of manufacturers lighting product data
- Does solar shading analysis, solar animations, renderings, glare/luminance ratios, interior illuminace, electric lighting integration
- Uses a radiosity engine with post process raytrace for renderings
Developed by: Lighting Analysts
Cost: Contact David Speer at dave@agi32.com
DAYSIM. This daylighting analysis software calculates the annual daylight availability as well as the lighting energy use of automated lighting controls (occupancy sensors, photocells) compared to standard on/off switches
- Radiance interface - combines backward raytracing with daylight coefficients approach
- Excellent for solar shading analysis, solar animiations, renderings, glare/luminance ratios and interior illuminance
- Simulation speed is on the slow side
Developed by: NRC-CNRC Institute for Research in Construction
Cost: Free download
ECOTECT. Ecotect is a building design and environmental analysis tool.
- Radiance interface with fast simulation speeds
- Ability to conduct climate analysis, solar shading analysis, solar animations, renderings, glare/luminance ratios and interior illuminances
- Ability to export to Radiance and Energy + for additional analysis
Developed by: Square One
Cost: Contact for pricing
Lumen Designer. Lumen Designer is the next generation of the popular LumenMicro.
- Fast
- Does solar shading analysis, solar animations, renderings, glare/luminance ratios, interior illuminace, electric lighting integration
- Uses a radiosity engine with post process raytrace for renderings (lumen micro used only a radiosity engine so was subject to those limitation)
- Analyzes complex interior lighting and daylighting systems including indirect light sources
Developed by: Lighting Technologies
Cost: Contact for pricing
Radiance. Radiance is a suite of programs for the analysis and visualization of lighting in design.
- Uses ray-tracing
- Predicts light levels
- Produces photo realistic gray scale renderings in all sky conditions
- Advanced lighting simulation and rendering tool
- Predicts illumination and visual quality within spaces
- Image library contributed by Radiance users
- Provides solar shading analysis, renderings, glare/luminance ratios, interior illumination, annual illuminance and electric lighting integration
Developed by: Lawrence Berkeley National Laboratory
Cost: Free download and image library
SkyCalc™. This simple tool assists designers in determining an effective toplighitng strategy that will achieve both electric lighting and HVAC savings.
- Design strategy (placement and number of recommended skylights) and building energy use patterns
- Ability to create weather files using eQuest 3.61 allowing use of the tool for any location in the world
Developed by: Heschong Mahone Group for Energy Design Resources
Cost: Free download
Solar 5. This energy design tool has been replaced by HEED for home energy analysis, but may be useful for some applications.
- Plots hourly energy performance in 3-d images for the entire building or various selected components
- Plots heat flows, indoor air temperature, daylighting, cost of electricity and heating fuel and air pollution
- Uses hour by hour weather data
Developed by: UCLA Department of Architecture and Urban Design
(contact milne@ucla.edu)
Cost: Free download
SPOT™ (Sensor Placement and Orientation Tool). This program was developed for the State of California's PIER program to assist in correct photosensor placement. It accounts for room geometry, surface reflectances, solar orientation, electric lighting layout and window design.
Developed by: Architectural Energy Corporation for State of California
Cost: Free download

Resources:

U.S. Department of Energy, Energy Efficiency and Renewable Energy Building Energy Software Tools Directory

References:

Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000.

IESNA Recommended Practice of Daylighting, IES: New York, 1999.

Presentation by Richard Keleher of Richard Keleher Architect at the Daylight Institute at LIGHTFAIR. May 6, 2007.

Presentation by Zack Rogers of AEC at the Velux Daylight Symposium, 2007.

Wasley, James. Integrated Daylight and Electric Lighting Laboratory Symposium Final Report. 2002.

Whole Building Design Guide.

RADIOSITY

< return to calculation methods

A basic description of radiosity is "the calculation method for expressing reflection." It is a computer graphics method to calculate diffuse light distribution and reflection in three dimensional environments. The resulting 3-D images are characterized by soft gradual shadows.

Calculation of radiosity is performed before rendering. Radiosity methods are used to determine the illuminace and luminance of a set of point located at the center of deferent surface elements. This determination can be made independent of view, before any surface rendering is made from a desired point of view. The calculation results provide information on the interaction of light with all surfaces in a room and the visibility of the shaded surfaces from different viewpoints.. When the result are applied to a rendered image, extremely realistic images can easily be created.

Radiosity algorithms compute how photons emitted from lights affect surfaces and store these results. The resulting information can then be used by a ray tracer to create a more realistic and physically correct image of a project. Radiosity methods are computationally intense, due to the use of linear systems of equations and the spatial complexity of large scenes.

Radiosity algorithms were originally developed for energy calculations to track surface elements exchanging light (radiant energy).

Exceptionally good for indoor spaces as it considers all light inter-reflections.

Radiosity software:

Agi32
AutoDesk VIZ
LumenDesigner

References:

Lighting Design Glossary / Lighting Design Knowledgebase.

Radiosity / by Allen Martin, Worcester Polytechnic Institute.

What is Radiosity? / by Fr�do Durand, Associate Professor in Electrical Engineering and Computer Science at the Massachusetts Institute of Technology.

Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000.

RAYTRACING

< return to calculation methods

Raytracing is a rendering technique that calculates an image of a scene by simulating the way rays of light travel in the real world. It is called raytracing because it tries to simulate the path that light rays take as they bounce around within a space - they are traced through the scene.

Raytracing is defined as the process of determining the visibility of surfaces by tracing imaginary rays of light from the viewer's eye to the objects of a rendered scene. This "backward" approach to tracing the rays of light from their end point to their source is most common, but there are other methods of raytracing calculations. Following is a more detailed explanation:

Backwards Raytracing is the process of following rays of light from the eye to the light source to produce an image (the opposite direction photons actually travel). A backward raytracing (the common approach, therefore referred to as simply ray-tracing) program calculates the illumination effects of a surface by tracking, or tracing, the path of a light ray as it bounces off or is refracted through the surface. Backward raytracing follows a light ray in the reverse direction, from the eye to the light source.

Forward Raytracing follows a ray from a light source in an arbitrary direction. Rays of light are emitted from a light source and illuminate objects. The light reflects off of the objects or passes through transparent objects. This reflected light hits our eyes. Forward raytracing programs simulate rays of light emanating from a light source, and determine where they end up when following a number of reflections on scene surfaces.

Because the vast majority of rays never hit an observer, it would take forever to trace a scene. Therefore, backwards raytracing has become the accepted method for this type of analysis.

Raytracing is normally used in the design of luminaire reflectors and other optical equipment.

Distributed Raytracing or Stochastic Raytracing simulates the diffuse light distribution and reflection in three dimensional environments. It is used in the Radiance software. Distributed raytracing simulates complex scenarios quite effectively. Radiosity is a better approach Exceptionally good for indoor spaces as it considers all light inter-reflections for scenes with high numbers of light sources.

Raytracing software:

Radiance
Ecotect
DAYSIM
SPOT
Adeline

References:

Ray Tracing: Graphics for the Masses / by Paul Rademacher.

Persistence of Vision™ Ray-Tracer POV-Ray™ Version 3.1g: What is Ray-Tracing? / Caltech's Center for Advanced Computing Research.

What is Raytracing? / by Siddhartha Chaudhuri.

Lighting Design Glossary / Lighting Design Knowledgebase.

Ray Tracing (presentation) / Carnegie Mellon School of Computer Science.

Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000.

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contact us join us	tools > design aids Daylighting Design Aids and Tools Analysis and simulation are important tools in daylighting design. You need both performance feedback and visual information to let you know how well the design functions in relation to your overall goals. The terms analysis and simulation are often used interchangeably to describe the various methods and tools that aid in daylighting and energy efficient design. In general, analysis provides quantitative information (annual available natural light, thermal impacts of natural lighting, solar shading analysis, etc.). Simulation is used to create a qualitative visual interpretation of what the space may actually be like (renderings). There are several tools and analysis methods available to help you assess your design. These include: Simple tools and calculations Physical modeling Computer modeling SIMPLE TOOLS AND CALCULATIONS Simple tools and calculations are used in the most preliminary of design concept stages to help determine the viability of daylighting. With the advent of computer tools that are fairly easy to use, these simple methods are becoming obsolete. Simple tools and calculations include: Sunpath diagrams to calculate available daylight during different seasons at different latitudes Daylight factor calculation for available interior daylight Glazing factor calculation for available interior daylight Fisheye photography for obstruction analysis PHYSICAL MODELING Physical modeling is exactly that—a physical to-scale model or full-scale mock-ups of your project to conduct daylighting availability analysis. Advantages: You are using real natural light The subtle qualities of light are accurately demonstrated Qualitative and quantitative information Can represent any room geometry Disadvantages: Cannot control the sun or weather Not easy to demonstrate design changes/iterations Need to build the model Local access to a heliodon or artificial sky Difficult to create a model with the appropriate textures and reflectances Difficult to mimic electric light sources Does not provide information on thermal impacts of daylighting or potential energy savings Physical model analysis methods include the use of the following as natural light sources: Heliodon (model can be manipulated to mimic various latitudes and times of day) Outdoor: use actual sky conditions and natural light to conduct analysis Indoor: use artificial light sources to mimic natural light Sky simulators (artificial sky) Mirror box—overcast sky simulator. Reports results as daylight factors Sky dome—can reproduce all types of skies Spotlight sky simulator—can reproduce all types of skies Scanning sky simulator For more information on using these analysis techniques, visit the various daylighting lab websites. These labs offer analysis services but unfortunately are located in only a few areas in the country. References: Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000. Overview of Daylight Simulation Tools / by Zack Rogers, PE, IESNA, LEED AP, Architectural Energy Corporation, LightLouver LLC, USA at the Daylight Symposium 2007. Presentation by Barbara Erwine of Cascadia Conservation at the Daylighting Institute, LIGHTFAIR, 2004. COMPUTER MODELING Today, the trend is toward computer analysis to provide daylighting design information and feedback immediately to the design team. Historically, these tools were sufficiently complex that only researchers involved with product development and/or primary field research were able to use them. Today, however, there are many tools available that have varying levels of complexity in both input required and output obtained. There are free programs available as well as ones for purchase. Advantages: Parametric in nature - when you change one design element the resulting effects on other design elements are automatically changed Some software provides three dimensional analysis Can be easy to learn Many programs have wizards to assist in model development Disadvantages: Some software can be costly Often difficult to find team member capable of completing the modeling Can be difficult to learn Many programs have wizards to assist in model development (be warned - many wizards must be changed to accurately provide results for your project - ESPECIALLY if using software to evaluate thermal impacts of daylighting) Depending on the goal of the analysis, software tools utilize different methods to achieve results and renderings. The categories of computer based tools are differentiated by the calculation methods they use: Radiosity (see detailed description below) Raytracing - backward and forward (see detailed description below) Software Tools This is not a comprehensive listing. If you would like information on a particular software tool, please contact us or refer to the resource links provided. Autodesk Viz. This 3D visualization software has tools for modeling, animation, lighting, and rendering. - Radiosity engine - Performs solar shading analysis and glare/luminance ratios to some degree - Strength is in solar animations, photorealistic animations and interior illumination Interoperable with AutoCAD applications Developed by: Autodesk Cost: Contact for pricing ADELINE (Advanced daylight and electric lighting integrated new environment). ADELINE is an integrated lighting design computer tool developed by an international research team within the framework of the International Energy Agency (IEA) Solar Heating and Cooling Programme Task 12. - Analyzes daylighting and electric lighting - Provides 3-D CAD modeling of space - Automatically generates Superlite and Radiance input files - Calculates interior illuminance levels in complex spaces primarily for large commercial buildings Developed by: Fraunhofer-Institute f�r Bauphysik Cost: Contact for pricing AGi32. This lighting analysis software program provides lighting calculations and renderings for electric lighting and daylighting system analysis. - Powerful and fast - Produces full-color renderings for daylighting and electric lighting analysis - Easily creates and analyzes complex environments - Includes comprehensive library of manufacturers lighting product data - Does solar shading analysis, solar animations, renderings, glare/luminance ratios, interior illuminace, electric lighting integration - Uses a radiosity engine with post process raytrace for renderings Developed by: Lighting Analysts Cost: Contact David Speer at dave@agi32.com DAYSIM. This daylighting analysis software calculates the annual daylight availability as well as the lighting energy use of automated lighting controls (occupancy sensors, photocells) compared to standard on/off switches - Radiance interface - combines backward raytracing with daylight coefficients approach - Excellent for solar shading analysis, solar animiations, renderings, glare/luminance ratios and interior illuminance - Simulation speed is on the slow side Developed by: NRC-CNRC Institute for Research in Construction Cost: Free download ECOTECT. Ecotect is a building design and environmental analysis tool. - Radiance interface with fast simulation speeds - Ability to conduct climate analysis, solar shading analysis, solar animations, renderings, glare/luminance ratios and interior illuminances - Ability to export to Radiance and Energy + for additional analysis Developed by: Square One Cost: Contact for pricing Lumen Designer. Lumen Designer is the next generation of the popular LumenMicro. - Fast - Does solar shading analysis, solar animations, renderings, glare/luminance ratios, interior illuminace, electric lighting integration - Uses a radiosity engine with post process raytrace for renderings (lumen micro used only a radiosity engine so was subject to those limitation) - Analyzes complex interior lighting and daylighting systems including indirect light sources Developed by: Lighting Technologies Cost: Contact for pricing Radiance. Radiance is a suite of programs for the analysis and visualization of lighting in design. - Uses ray-tracing - Predicts light levels - Produces photo realistic gray scale renderings in all sky conditions - Advanced lighting simulation and rendering tool - Predicts illumination and visual quality within spaces - Image library contributed by Radiance users - Provides solar shading analysis, renderings, glare/luminance ratios, interior illumination, annual illuminance and electric lighting integration Developed by: Lawrence Berkeley National Laboratory Cost: Free download and image library SkyCalc™. This simple tool assists designers in determining an effective toplighitng strategy that will achieve both electric lighting and HVAC savings. - Design strategy (placement and number of recommended skylights) and building energy use patterns - Ability to create weather files using eQuest 3.61 allowing use of the tool for any location in the world Developed by: Heschong Mahone Group for Energy Design Resources Cost: Free download Solar 5. This energy design tool has been replaced by HEED for home energy analysis, but may be useful for some applications. - Plots hourly energy performance in 3-d images for the entire building or various selected components - Plots heat flows, indoor air temperature, daylighting, cost of electricity and heating fuel and air pollution - Uses hour by hour weather data Developed by: UCLA Department of Architecture and Urban Design (contact milne@ucla.edu) Cost: Free download SPOT™ (Sensor Placement and Orientation Tool). This program was developed for the State of California's PIER program to assist in correct photosensor placement. It accounts for room geometry, surface reflectances, solar orientation, electric lighting layout and window design. Developed by: Architectural Energy Corporation for State of California Cost: Free download Resources: U.S. Department of Energy, Energy Efficiency and Renewable Energy Building Energy Software Tools Directory References: Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000. IESNA Recommended Practice of Daylighting, IES: New York, 1999. Presentation by Richard Keleher of Richard Keleher Architect at the Daylight Institute at LIGHTFAIR. May 6, 2007. Presentation by Zack Rogers of AEC at the Velux Daylight Symposium, 2007. Wasley, James. Integrated Daylight and Electric Lighting Laboratory Symposium Final Report. 2002. Whole Building Design Guide. RADIOSITY < return to calculation methods A basic description of radiosity is "the calculation method for expressing reflection." It is a computer graphics method to calculate diffuse light distribution and reflection in three dimensional environments. The resulting 3-D images are characterized by soft gradual shadows. Calculation of radiosity is performed before rendering. Radiosity methods are used to determine the illuminace and luminance of a set of point located at the center of deferent surface elements. This determination can be made independent of view, before any surface rendering is made from a desired point of view. The calculation results provide information on the interaction of light with all surfaces in a room and the visibility of the shaded surfaces from different viewpoints.. When the result are applied to a rendered image, extremely realistic images can easily be created. Radiosity algorithms compute how photons emitted from lights affect surfaces and store these results. The resulting information can then be used by a ray tracer to create a more realistic and physically correct image of a project. Radiosity methods are computationally intense, due to the use of linear systems of equations and the spatial complexity of large scenes. Radiosity algorithms were originally developed for energy calculations to track surface elements exchanging light (radiant energy). Exceptionally good for indoor spaces as it considers all light inter-reflections. Radiosity software: Agi32 AutoDesk VIZ LumenDesigner References: Lighting Design Glossary / Lighting Design Knowledgebase. Radiosity / by Allen Martin, Worcester Polytechnic Institute. What is Radiosity? / by Fr�do Durand, Associate Professor in Electrical Engineering and Computer Science at the Massachusetts Institute of Technology. Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000. RAYTRACING < return to calculation methods Raytracing is a rendering technique that calculates an image of a scene by simulating the way rays of light travel in the real world. It is called raytracing because it tries to simulate the path that light rays take as they bounce around within a space - they are traced through the scene. Raytracing is defined as the process of determining the visibility of surfaces by tracing imaginary rays of light from the viewer's eye to the objects of a rendered scene. This "backward" approach to tracing the rays of light from their end point to their source is most common, but there are other methods of raytracing calculations. Following is a more detailed explanation: Backwards Raytracing is the process of following rays of light from the eye to the light source to produce an image (the opposite direction photons actually travel). A backward raytracing (the common approach, therefore referred to as simply ray-tracing) program calculates the illumination effects of a surface by tracking, or tracing, the path of a light ray as it bounces off or is refracted through the surface. Backward raytracing follows a light ray in the reverse direction, from the eye to the light source. Forward Raytracing follows a ray from a light source in an arbitrary direction. Rays of light are emitted from a light source and illuminate objects. The light reflects off of the objects or passes through transparent objects. This reflected light hits our eyes. Forward raytracing programs simulate rays of light emanating from a light source, and determine where they end up when following a number of reflections on scene surfaces. Because the vast majority of rays never hit an observer, it would take forever to trace a scene. Therefore, backwards raytracing has become the accepted method for this type of analysis. Raytracing is normally used in the design of luminaire reflectors and other optical equipment. Distributed Raytracing or Stochastic Raytracing simulates the diffuse light distribution and reflection in three dimensional environments. It is used in the Radiance software. Distributed raytracing simulates complex scenarios quite effectively. Radiosity is a better approach Exceptionally good for indoor spaces as it considers all light inter-reflections for scenes with high numbers of light sources. Raytracing software: Radiance Ecotect DAYSIM SPOT Adeline References: Ray Tracing: Graphics for the Masses / by Paul Rademacher. Persistence of Vision™ Ray-Tracer POV-Ray™ Version 3.1g: What is Ray-Tracing? / Caltech's Center for Advanced Computing Research. What is Raytracing? / by Siddhartha Chaudhuri. Lighting Design Glossary / Lighting Design Knowledgebase. Ray Tracing (presentation) / Carnegie Mellon School of Computer Science. Daylight in Buildings: A Source Book on Daylighting Systems and Components, International Energy Agency - A Report of IEA SHC Task 21; Lawrence Berkeley National Laboratory, Berkeley, CA: 2000.