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Daylighting Resources - Windows and Window Treatments

Mechanical Shade Control Device
A small demonstration and evaluation of a mechanical shade control device developed by the University of Oregon's Energy Studies in Buildings Laboratory was undertaken to determine the device's operational issues, building occupant acceptance and energy saving capabilities when used with lighting photocell controls. There are two reports on the mechanical shade controll device, one from the test sites at the University of Oregon and the second from the test sites at the Lighting Research Center.

How Much Energy Do Sidelighting Strategies Save? PDF - (2006): Windows can introduce considerable heat gains and losses that may offset the benefits of electric light energy savings and cause an increase in yearly net energy use. The use of shading devices is necessary to prevent overheating and to provide a glare-free visual environment. The most common shading devices that have been in use in buildings are exterior overhangs, interior blinds and roller shades. This study examines the impacts of these devices on the toatl yearly energy loads of a building.

Are Windows and Views Really Better? PDF - (2005): A quantitative analysis of the Economic and Psychological Value of Views.

Blinds

Title: Innovative daylighting: Review of systems and evaluation methods
Author(s): Littlefair, PJ
Reference: Littlefair, P.J. (1990). Innovative daylighting: review of systems and evaluation methods. Lighting Research and Technology 22(1), 1-17.
Abstract: A survey of advanced daylighting technologies, including sun-gathering heliostat-lightpipe systems, light shelves, prismatic and holographic glazing. This report finds that heliostat systems are ineffective for general illumination; a 2m (6’) diameter mirror would produce only as much useful light as seven 1.5m (5’) fluorescent tubes, and would only work when the sun shines. Light shelves are found to be effective at increasing the light level at the back of a room, but only when the sun shines; otherwise they reduce the total amount of daylight in the room. Blinds are still required in addition to light shelves, to block low-angle winter sun. In general, light-gathering and redirecting systems are found to reduce the total amount of daylight entering a space, although they subdue glare from direct sunlight, and redirect diffuse light onto surfaces around the window to reduce window glare.

Title: Window blind occlusion: A pilot study, building and environment
Author(s): Rea, MS
Reference: Rea, M.S., (1984) Window blind occlusion: A pilot study, Building and Environment, 19, 133-137.
Abstract: Building occupants seldom adjust their window blinds during the course of the day; they tend to leave their blinds closed even when glare-free diffuse daylight could be admitted. Window blinds are typically more than 50% occluded. It might be expected that occupants would close blinds to exclude sunlight, and open them again under cloudy skies to admit more daylight, but results suggest that occupants set their blinds to a position in which solar glare is sufficiently excluded under most sky conditions, and leave the blinds in that position for weeks, months or years. 555 window blinds in an office building were monitored using photographs of the façade. The east, south and west facades had an average of 50%, 66% and 62% occlusion respectively. Between cloudy days and sunny days, these occlusions varied up or down from the average by 10%, 1% and 2% respectively. The east façade showed significantly more variation than the other facades, though no explanation for this is offered. These results are similar to results found previously by Rubin.

Title: Advanced optical daylighting systems: Light shelves and light pipes
Author(s): Beltran, LO, Lee, ES, Selkowitz, SE
Reference: Beltran, L.O., Lee, E.S. and Selkowitz, S.E. (1997). Advanced optical daylighting systems : light shelves and light pipes. Journal of the Illuminating Engineering Society of North America, 26(2), 91-106
Abstract: This study gives numerical values for light levels and potential lighting energy savings for several daylight redirection systems. These included single and multi-level light shelves with both matt and specular top surfaces, and sealed specular ‘light pipes’ hidden within the ceiling void. All systems were intended to reduce light levels near the window and redirect light to the back of the space. Calculations under one year of ‘average’ skies, i.e., a statistically typical combination of sunny and overcast conditions, showed that standard clear glass windows gave the highest light levels and highest potential lighting energy savings. Prismatic light pipes gave the second highest energy savings, and light shelves the lowest. Of the light shelf designs tested, the ‘base case’ design gave highest potential lighting electricity saving. Under sunny skies, all the specular light shelves and light pipes were effective at increasing light levels at the back of the space, compared to standard clear glass windows. The light pipes used in the study take up a significant proportion of the ceiling void and would necessitate unorthodox HVAC ducting.

Title: Effects of interior design on daylight availability in open-plan offices
Author(s): Reinhart, CF
Publication Organization: National Research Council of Canada
Publication URL: http://irc.nrc-cnrc.gc.ca/fulltext/nrcc45374/nrcc45374.pdf
Abstract: An investigation of the daylighting effect of design variables including: blinds, partition height, and ceiling and partition reflectance. The results show that, when complemented by a daylight-linked lighting system, blinds closed at 45 degrees can save up to 26% of lighting energy, manual blinds can save 41%, and automatic blinds 58%; all energy savings are in comparison to full installed load. Peripheral offices can typically save 25%-60% of their lighting energy by daylight-linking, and second-row offices can save 20%-40%. The results were obtained by computer modelling of a south-facing office with ribbon windows and clear glazing, using New York City climatic data.

Title: Tips for daylighting with windows: Shading strategy (pages 5-1 to 5-5)
Author(s): O'Connor, J, Lee, ES, Rubinstein, F, Selkowitz, S
Publication Organization: Lawrence Berkeley National Laboratory
Publication URL: http://windows.lbl.gov/pub/designguide/section5.pdf
Abstract: A step-by-step guide to choosing, sizing and specifying architectural window shades. Many sketches are used to show the various design options, and how each one modifies the way the daylight is admitted in to the building. The use of sunpath diagrams to design window shading is clearly explained. Key items are checklisted in order of priority to help the time-pressured architect.

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Light Shelves

Title: Innovative daylighting: Review of systems and evaluation methods
Author(s): Littlefair, PJ
Reference: Littlefair, P.J. (1990). Innovative daylighting: review of systems and evaluation methods. Lighting Research and Technology 22(1), 1-17.
Abstract: A survey of advanced daylighting technologies, including sun-gathering heliostat-lightpipe systems, light shelves, prismatic and holographic glazing. This report finds that heliostat systems are ineffective for general illumination; a 2m (6’) diameter mirror would produce only as much useful light as seven 1.5m (5’) fluorescent tubes, and would only work when the sun shines. Light shelves are found to be effective at increasing the light level at the back of a room, but only when the sun shines; otherwise they reduce the total amount of daylight in the room. Blinds are still required in addition to light shelves, to block low-angle winter sun. In general, light-gathering and redirecting systems are found to reduce the total amount of daylight entering a space, although they subdue glare from direct sunlight, and redirect diffuse light onto surfaces around the window to reduce window glare.

Title: Advanced optical daylighting systems: Light shelves and light pipes
Author(s): Beltran, LO, Lee, ES, Selkowitz, SE
Reference: Beltran, L.O., Lee, E.S. and Selkowitz, S.E. (1997). Advanced optical daylighting systems : light shelves and light pipes. Journal of the Illuminating Engineering Society of North America, 26(2), 91-106
Abstract: This study gives numerical values for light levels and potential lighting energy savings for several daylight redirection systems. These included single and multi-level light shelves with both matt and specular top surfaces, and sealed specular ‘light pipes’ hidden within the ceiling void. All systems were intended to reduce light levels near the window and redirect light to the back of the space. Calculations under one year of ‘average’ skies, i.e., a statistically typical combination of sunny and overcast conditions, showed that standard clear glass windows gave the highest light levels and highest potential lighting energy savings. Prismatic light pipes gave the second highest energy savings, and light shelves the lowest. Of the light shelf designs tested, the ‘base case’ design gave highest potential lighting electricity saving. Under sunny skies, all the specular light shelves and light pipes were effective at increasing light levels at the back of the space, compared to standard clear glass windows. The light pipes used in the study take up a significant proportion of the ceiling void and would necessitate unorthodox HVAC ducting.

Title: Enclosure systems
Publication Organization: Northwest Energy Alliance (Better Bricks)
Publication URL: http://www.betterbricks.com/graphics/assets/documents/DesignSystemEnvelopguideline_pa.pdf
Abstract: Discussion of the available options for building enclosure (facade) systems, including external shading devices and internal light shelves. The effect of these systems on visual comfort inside buildings, and upon HVAC systems is discussed. Visual comfort issues include: avoiding excessive contrast and solar glare; maximizing the amount of natural light and visual stimulation. The limitations of light shelves and external shading devices are described, along with the importance of multi-factorial design in producing successful buildings. Differences in local climate are addressed, and a checklist for successful design is provided.

Title: Advanced Lighting Guidelines, pages 7-19 to 7-22, 7-35 to 7-38
Author(s): Benya, J, Heschong, L, McGowan, T, Miller, NJ
Publication Organization: New Buildings Institute
Publication URL: http://www.newbuildings.org/lighting.htm
Abstract: This section of the Advanced Lighting Guidelines contains information about the technologies and techniques available for shading and daylight redirection, including external louvers, light shelves and opaque blinds. Photographs of installed systems are shown. Practical advice on the design and positioning of light shelves, though no quantitative information about the effect of these devices on light distribution is given. Click on "Advanced Lighting Guidelines: 2003 Edition" on the site's homepage to view reference. Site requires submittal of user information to view PDF file.

Title: Tips for daylighting with windows: Shading strategy (pages 5-1 to 5-5)
Author(s): O'Connor, J, Lee, ES, Rubinstein, F, Selkowitz, S
Publication Organization: Lawrence Berkeley National Laboratory
Publication URL: http://windows.lbl.gov/pub/designguide/section5.pdf
Abstract: A step-by-step guide to choosing, sizing and specifying architectural window shades. Many sketches are used to show the various design options, and how each one modifies the way the daylight is admitted in to the building. The use of sunpath diagrams to design window shading is clearly explained. Key items are checklisted in order of priority to help the time-pressured architect.

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Shading Devices

Title: The significance of sunshine and view for office workers
Author(s): Markus, TA
Reference: Markus, T.A., (1967) The significance of sunshine and view for office workers, in R.G. Hopkinson (ed) Sunlight in Buildings, Boewcentrum International: Rotterdam, The Netherlands.
Abstract: In an extensive study, 95% of office occupants preferred daylight to electric lighting. Those nearer to windows were more satisfied with their daylight than those further away, particularly on the lower floors. This effect could be attributable to the view out of the building, or to the amount of daylight. Occupants near the south-east and south-west walls were more satisfied with their daylight than those near the north-west and north-east walls. This may be because they value the availability of direct sunlight, or it may be due to window glare being more severe through north-facing windows. The study surveyed 400 office workers on nine floors of a 12-story open-plan building.

Title: Effect of window size and sunlight presence on glare
Author(s): Boubekri, M, Boyer, LL
Reference: Boubekri, M. and L. L. Boyer (1992), Effect of Window Size and Sunlight Presence on Glare, Lighting Research and Technology, 24 (2): 69-74
Abstract: Occupants’ assessments of glare from south-facing windows were found to be lower than predicted by daylight glare index calculations. The authors ascribe this difference to the presence of direct sunlight, and to the pleasant rural view from the window. Daylight glare varied according to window area, reaching a maximum when the windows occupied 50% of the facade. Fifty percent is a typical value for many commercial buildings, so the results suggest that current daylighting practice may be suboptimal with regard to glare.

Title: Windows and daylight - A post-occupancy evaluation of offices
Author(s): Christoffersen, J, Petersen, E, Johnsen, K, Valbjorn, O
Reference: Statens Byggeforskningsinstitut. (1999). Report 318: Windows and Daylight - a Post-occupancy Evaluation of Offices. Horsholm, Denmark.
Publication Organization: Statens Byggeforskningsinstitut, Horsholm, Denmark
Abstract: A survey of 2340 Danish office workers found that there is a strong preference for having the workstation close to a window, despite a higher incidence of glare and reflections on PC screens. Occupants' satisfaction with their daylighting was strongly positively correlated with measured daylight factor. Sixty percent of occupants wished to have direct sunlight in their office during at least one season of the year. More than 50% of respondents reported no negative aspects of their windows; of the problems reported, glare was the most frequent, followed by heat discomfort. The degree of dissatisfaction with daylighting increased with the number of people in the office.

Title: Productivity in buildings: The "killer" variables
Author(s): Leaman, A, Bordass, B
Reference: Leaman, A., and Bordass, B. (2000) Productivity in buildings: The "killer" variables, in Creating the Productive Workplace, ed: D. Clements-Croome, E. & F. N. Spon: London.
Abstract: An extensive series of post-occupancy evaluations of office buildings (known as the ‘PROBE’ studies) led to the identification of four ‘killer’ variables that have a critical influence on productivity. These are labeled ‘personal control’, ‘responsiveness to complaints’, ‘building depth’, and ‘workgroup’. Designers can influence ‘personal control’ by designing easy-to-use lighting and ventilation control systems, and openable windows. Designers can also influence ‘building depth.’ For ‘personal control’ there was a small but statistically significant correlation (r = 0.16 to 0.49) between level of individual control of the environment and self-reported productivity in seven of eleven office buildings evaluated. Results suggest that personal control is most valued when there is a source of discomfort such as glare or solar heat, i.e., when personal control enables the individual to adjust the conditions until comfort is achieved. For this reason, all windows should have some means of controlling the admission of daylight and sunlight to ensure comfort. For ‘building depth’, as buildings get deeper, the levels of satisfaction with the building and self-reported productivity decrease. The critical threshold depth appears to be about 15 m (50’) from wall to wall, when both walls are glazed. The percentage of people satisfied with the building was closely correlated with the percentage of people sitting next to windows.

Title: Window blind occlusion: A pilot study, building and environment
Author(s): Rea, MS
Referenc: Rea, M.S., (1984) Window blind occlusion: A pilot study, Building and Environment, 19, 133-137.
Abstract: Building occupants seldom adjust their window blinds during the course of the day; they tend to leave their blinds closed even when glare-free diffuse daylight could be admitted. Window blinds are typically more than 50% occluded. It might be expected that occupants would close blinds to exclude sunlight, and open them again under cloudy skies to admit more daylight, but results suggest that occupants set their blinds to a position in which solar glare is sufficiently excluded under most sky conditions, and leave the blinds in that position for weeks, months or years. 555 window blinds in an office building were monitored using photographs of the façade. The east, south and west facades had an average of 50%, 66% and 62% occlusion respectively. Between cloudy days and sunny days, these occlusions varied up or down from the average by 10%, 1% and 2% respectively. The east façade showed significantly more variation than the other facades, though no explanation for this is offered. These results are similar to results found previously by Rubin.

Title: Enclosure systems
Publication Organization: Northwest Energy Alliance (Better Bricks)
Publication URL: http://www.betterbricks.com/graphics/assets/documents/DesignSystemEnvelopguideline_pa.pdf
Abstract: Discussion of the available options for building enclosure (facade) systems, including external shading devices and internal light shelves. The effect of these systems on visual comfort inside buildings, and upon HVAC systems is discussed. Visual comfort issues include: avoiding excessive contrast and solar glare; maximizing the amount of natural light and visual stimulation. The limitations of light shelves and external shading devices are described, along with the importance of multi-factorial design in producing successful buildings. Differences in local climate are addressed, and a checklist for successful design is provided.

Title: Advanced Lighting Guidelines, pages 7-19 to 7-22, 7-35 to 7-38
Author(s): Benya, J, Heschong, L, McGowan, T, Miller, NJ
Publication Organization: New Buildings Institute
Publication URL: http://www.newbuildings.org/lighting.htm
Abstract: This section of the Advanced Lighting Guidelines contains information about the technologies and techniques available for shading and daylight redirection, including external louvers, light shelves and opaque blinds. Photographs of installed systems are shown. Practical advice on the design and positioning of light shelves, though no quantitative information about the effect of these devices on light distribution is given. Click on "Advanced Lighting Guidelines: 2003 Edition" on the site's homepage to view reference. Site requires submittal of user information to view PDF file.

Title: Tips for daylighting with windows: Shading strategy (pages 5-1 to 5-5)
Author(s): O'Connor, J, Lee, ES, Rubinstein, F, Selkowitz, S
Publication Organization: Lawrence Berkeley National Laboratory
Publication URL: http://windows.lbl.gov/pub/designguide/section5.pdf Abstract: A step-by-step guide to choosing, sizing and specifying architectural window shades. Many sketches are used to show the various design options, and how each one modifies the way the daylight is admitted in to the building. The use of sunpath diagrams to design window shading is clearly explained. Key items are checklisted in order of priority to help the time-pressured architect.

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Windows

Title: LEED Green Building Rating System
Author(s): LEED (Leadership in Energy and Environmental Design)
Reference: LEED (Leadership in Energy and Environmental Design)
Publication Organization: US Green Building Council
Publication URL: http://www.usgbc.org/LEED/LEED_main.asp
Abstract: The LEED (Leadership in Energy and Environmental Design) Green Building Rating System™ is a voluntary, consensus-based, national standard for developing high-performance, sustainable buildings. LEED certification assures the tenant that a building reaches high standards of energy performance, while creating comfortable environmental conditions for occupants. Of the 69 credits available for new contrusction within the LEED system, one can be obtained by assuring a minimum of 2% daylight factor over 75% of the floorspace, and another can be obtained by ensuring a direct line of sight to vision glazing from 90% of the floorspace. Similar LEED credits designations are being developed for existing building, commercial interiors, and core and shell projects.

Title: California Energy Commission 2005 Building Energy Efficiency Standards (Title 24)
Author(s): G. William Pennington, Jon Leber
Reference: G. William Pennington, Jon Leber
Publication Organization: California Energy Commission
Publication URL: www.energy.ca.gov/title24/2005standards/index.html
Abstract: The California Building Code establishes building energy efficiency standards for new construction (including requirements for entire new buildings, additions, alterations, and in non-residential buildings, repairs). The Code requires that office buildings use no more than 1.1w ft2 for lighting; this figure is very difficult to achieve without the use of 'adjustment factors' which take account of the presence of lighting control systems, including daylight linking. Large windows with high transmittance glazing allow adjustment factors of up to 40% to be used. The next update to California's energy efficiency standards for residential and non-residential buildings (Title 24, Part 6) is expected to be adopted by the Commission by July 1, 2003, and go into effect in 2005.

Title: The significance of sunshine and view for office workers
Author(s): Markus, TA
Reference: Markus, T.A., (1967) The significance of sunshine and view for office workers, in R.G. Hopkinson (ed) Sunlight in Buildings, Boewcentrum International: Rotterdam, The Netherlands.
Abstract: In an extensive study, 95% of office occupants preferred daylight to electric lighting. Those nearer to windows were more satisfied with their daylight than those further away, particularly on the lower floors. This effect could be attributable to the view out of the building, or to the amount of daylight. Occupants near the south-east and south-west walls were more satisfied with their daylight than those near the north-west and north-east walls. This may be because they value the availability of direct sunlight, or it may be due to window glare being more severe through north-facing windows. The study surveyed 400 office workers on nine floors of a 12-story open-plan building.

Title: Effect of window size and sunlight presence on glare
Author(s): Boubekri, M, Boyer, LL
Reference: Boubekri, M. and L. L. Boyer (1992), Effect of Window Size and Sunlight Presence on Glare, Lighting Research and Technology, 24 (2): 69-74
Abstract: Occupants’ assessments of glare from south-facing windows were found to be lower than predicted by daylight glare index calculations. The authors ascribe this difference to the presence of direct sunlight, and to the pleasant rural view from the window. Daylight glare varied according to window area, reaching a maximum when the windows occupied 50% of the facade. Fifty percent is a typical value for many commercial buildings, so the results suggest that current daylighting practice may be suboptimal with regard to glare.

Title: Glare from windows -3. Using the glare index in daylighting design
Author(s): Hopkinson, R
Reference: Hopkinson, R. G. (1971) Glare from windows - 3 using the glare index in daylighting design. Construction Research and Development Journal 3(1), 23-28.
Abstract: Interior window reveals can reduce glare from windows. Reveals are usually sections of light-colored angled wall surrounding a window, and are used to create an area of intermediate luminance between the window and the interior wall. A window surrounded by a reveal of one-sixth of its linear dimension can reduce glare by up to two points on a 12-point scale ranging from 16 (imperceptible) to 25 (intolerable).

Title: Daylight and the appearance of indoor surfaces
Author(s): Lynes, J
Reference: Lynes, J. (1994). “Daylight and the appearance of indoor surfaces.” Proceedings of the CIBSE National Lighting Conference 1994, 98-110.
Abstract: High contrasts (glare) around windows make it impossible for occupants to distinguish colors on surfaces immediately surrounding the window. This ‘failure of lightness constancy’ can be characterized as ‘gloom’ and plausibly accounts for the observed tendency of people to switch electric lighting on when they enter a room. Electric lighting reduces the contrast between the window and the wall, and makes colors visible once more. Glare and gloom are closely linked, and both can be reduced by increasing the ‘daylight factor', i.e., by adding more daylight into the room. Lynes provides graphs that can be used to determine the minimum value of wall reflectance for a given daylight factor (or vice-versa). Lynes’ calculations are based on Hunt’s (1991) color model.

Title: Circadian photobiology: An emerging framework for lighting practice and research
Author(s): Rea, MS, Figueiro, MG, Bullough, JD
Reference: Rea, Mark S., Mariana G. Figueiro, and John D. Bullough. (2002) Circadian Photobiology: an Emerging Framework for Lighting Practice and Research. Lighting Research and Technology 34(3), 177-190.
Abstract: Lighting can be used to strengthen the human circadian rhythm, which determines various physiological functions such as sleep, digestion, alertness, depression, and probably general health. Daylight is much more effective than electric lighting at ‘entraining’ the circadian system; this is because the circadian system responds only to high levels of blue light, such as those found in daylight. Rea et al. calculate ‘circadian efficacies’ for various light sources, and find that daylight is three to four times more effective than fluorescent lamps, and twenty times more effective than incandescent lamps. They find that "light levels approaching those found outdoors in daylight are sufficient for regulation of the circadian clock and the melatonin cycle, but many indoor light levels are too low."

Title: Status in organizations: Where evolutionary theory ranks
Author(s): Waldron, D
Reference: Waldron, D. (1998). Status in Organizations: Where Evolutionary Theory Ranks. Managerial and Decision Economics (19), 505-520.
Abstract: The desire for status is one of the strongest sources of motivation for employees. This paper cites Halloran (1978) in stating that proximity to windows, and the number of windows in an office, is a common and widely understood expression of status. The author does not discuss whether the provision of windows enhances the overall status of a building or a company, or whether the effect exists only within organizations. The author makes a distinction between status and hierarchy: the former being an informal system of signs (“status symbols”) and behaviors; the latter being a more formal organizational structure expressed in job titles and remuneration. Status appears to be a pervasive phenomenon in organizations, as it is in all societies, and may be genetically or instinctually based since it is exhibited by other ape species.

Title: Innovative daylighting: Review of systems and evaluation methods
Author(s): Littlefair, PJ
Reference: Littlefair, P.J. (1990). Innovative daylighting: review of systems and evaluation methods. Lighting Research and Technology 22(1), 1-17.
Abstract: A survey of advanced daylighting technologies, including sun-gathering heliostat-lightpipe systems, light shelves, prismatic and holographic glazing. This report finds that heliostat systems are ineffective for general illumination; a 2m (6’) diameter mirror would produce only as much useful light as seven 1.5m (5’) fluorescent tubes, and would only work when the sun shines. Light shelves are found to be effective at increasing the light level at the back of a room, but only when the sun shines; otherwise they reduce the total amount of daylight in the room. Blinds are still required in addition to light shelves, to block low-angle winter sun. In general, light-gathering and redirecting systems are found to reduce the total amount of daylight entering a space, although they subdue glare from direct sunlight, and redirect diffuse light onto surfaces around the window to reduce window glare.

Title: Minimum acceptable transmittance of glazing
Author(s): Boyce, P
Reference: Boyce, P. (1995). Minimum acceptable transmittance of glazing. Lighting Research and Technology 27(3), 145-152
Abstract: Tinted windows with low transmittances should not be used, because occupants rate them as being ‘too dark.' Occupant acceptance of tinted windows falls below 85% when visible light transmittance is around 38% under overcast (cloudy) skies, though transmittances as low as 25% may be acceptable under clear (sunny) skies. The color of the glass—neutral or bronze—was found to slightly affect the minimum acceptable transmittance, but not in a consistent or predictable way. Real window glass samples were used in a 1/12 scale model office placed outdoors. The model office had a ribbon window occupying 42% of the wall area. There were no windows in the other walls. The authors do not suggest upon what basis occupants make their judgments of acceptability.

Title: Enclosure systems
Publication Organization: Northwest Energy Alliance (Better Bricks)
Publication URL: www.betterbricks.com/graphics/assets/documents/DesignSystemEnvelopguideline_pa.pdf
Abstract: Discussion of the available options for building enclosure (facade) systems, including external shading devices and internal light shelves. The effect of these systems on visual comfort inside buildings, and upon HVAC systems is discussed. Visual comfort issues include: avoiding excessive contrast and solar glare; maximizing the amount of natural light and visual stimulation. The limitations of light shelves and external shading devices are described, along with the importance of multi-factorial design in producing successful buildings. Differences in local climate are addressed, and a checklist for successful design is provided.

Title: Which glass should I use? Sorting it all out
Publication Organization: Northwest Energy Alliance (Better Bricks)
Publication URL: www.betterbricks.com/DetailPage.aspx?ID=808
Abstract: A guide to the main parameters determining glazing performance, including visible light transmission (VLT), solar heat gain coefficient (SHGC), and U-factor. Advice on the selection of glazing is given: what VLT to choose; when to use clear versus diffuse glass; the benefits of fritting; laminates and smart windows. The National Fenestration Rating Council is cited as a good source of theoretical and practical information.

Title: Advanced Lighting Guidelines, pages 7-24 to 7-28
Author(s): Benya, J, Heschong, L, McGowan, T, Miller, NJ
Reference: Benya, Heschong, McGowan, Miller, Rubinstein
Publication Organization: New Buildings Institute
Publication URL: http://www.newbuildings.org/lighting.htm
Abstract: This section of the Advanced Lighting Guidelines contains definitions of key window performance parameters including U-factor, solar heat gain coefficient, visible light transmittance. A table of typical values for various glass types is given. The materials and techniques used in manufacturing low-emissivity coatings, diffusing glass, tinted glass and fritted glass are discussed. Some conceptual advice on sizing and positioning of windows is given on page 7-35. Click on "Advanced Lighting Guidelines: 2003 Edition" on the site's homepage to view reference. Site requires submittal of user information to view PDF file.

Title: Design Brief: Glazing
Publication Organization: Energy Design Resources
Publication URL: http://www.energydesignresources.com/resource/20/
Abstract: This document introduces the principles used to assess the performance of glazing, including transmission and reflectance values, and the effect of glazing on the spectral distribution of indoor light. Glazing terminology such as "thermal break" and "low-emissivity" is also explained. Examples are given of a whole-building lifecycle analysis and future glazing technologies are discussed. Special consideration is given to California energy codes.

Title: Tips for daylighting with windows: Envelope and room decisions (pages 3-1 to 3-7)
Author(s): O'Connor, J, Lee, ES, Rubinstein, F, Selkowitz, S
Publication Organization: Lawrence Berkeley National Laboratory
Publication URL: http://windows.lbl.gov/pub/designguide/section3.pdf
Abstract: This guide gives design advice that explores the purpose, positioning, sizing and detailing of windows. Many sketches are used to show a wide range of possible design options, and the consequences of design choices such as glazing transmission, room depth, furniture layout, desk orientation, and light shelves.

Title: Window Systems for High-Performance Buildings
Author(s): John Carmody, et. al.
Reference: Carmody, John, et. al., (2004), Window Systems for High-Performance Buildings, W. W. Norton & Company, Inc., 500 Fifth Avenue, New York, NY 10110
Abstract: This reference book guides the reader through the selection and design of window systems for commercial buildings. It presents information on different window materials and assemblies and their effect on energy use, daylighting strategies, glare, view and thermal comfort. The book describes a decision making process for selecting windows for different climates and for different building facade orientations.

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Window Designs

Title: Effect of window size and sunlight presence on glare
Author(s): Boubekri, M, Boyer, LL
Reference: Boubekri, M. and L. L. Boyer (1992), Effect of Window Size and Sunlight Presence on Glare, Lighting Research and Technology, 24 (2): 69-74
Abstract: Occupants’ assessments of glare from south-facing windows were found to be lower than predicted by daylight glare index calculations. The authors ascribe this difference to the presence of direct sunlight, and to the pleasant rural view from the window. Daylight glare varied according to window area, reaching a maximum when the windows occupied 50% of the facade. Fifty percent is a typical value for many commercial buildings, so the results suggest that current daylighting practice may be suboptimal with regard to glare.

Title: Glare from windows -3. Using the glare index in daylighting design
Author(s): Hopkinson, R
Reference: Hopkinson, R. G. (1971) Glare from windows - 3 using the glare index in daylighting design. Construction Research and Development Journal 3(1), 23-28.
Abstract: Interior window reveals can reduce glare from windows. Reveals are usually sections of light-colored angled wall surrounding a window, and are used to create an area of intermediate luminance between the window and the interior wall. A window surrounded by a reveal of one-sixth of its linear dimension can reduce glare by up to two points on a 12-point scale ranging from 16 (imperceptible) to 25 (intolerable).

Title: Innovative daylighting: Review of systems and evaluation methods
Author(s): Littlefair, PJ
Reference: Littlefair, P.J. (1990). Innovative daylighting: review of systems and evaluation methods. Lighting Research and Technology 22(1), 1-17.
Abstract: A survey of advanced daylighting technologies, including sun-gathering heliostat-lightpipe systems, light shelves, prismatic and holographic glazing. This report finds that heliostat systems are ineffective for general illumination; a 2m (6’) diameter mirror would produce only as much useful light as seven 1.5m (5’) fluorescent tubes, and would only work when the sun shines. Light shelves are found to be effective at increasing the light level at the back of a room, but only when the sun shines; otherwise they reduce the total amount of daylight in the room. Blinds are still required in addition to light shelves, to block low-angle winter sun. In general, light-gathering and redirecting systems are found to reduce the total amount of daylight entering a space, although they subdue glare from direct sunlight, and redirect diffuse light onto surfaces around the window to reduce window glare.

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SPONSORED BY:
California Energy Commission
Connecticut Light & Power
Efficiency Vermont
Lighting Research Center
North Carolina Daylighting Consortium
Northwest Energy Efficiency Alliance
NYSERDA
US Department of Energy