DAYLIGHT IN BUILDING DESIGN

DAYLIGHT IN BUILDING DESIGN

CHAPTER 1

INTRODUCTION

In a world newly concerned about carbon emissions, global warming, and sustainable design, the planned use of natural light in non-residential buildings has become an important strategy to improve energy efficiency by minimizing lighting, heating, and cooling loads. The introduction of innovative, advanced daylighting strategies and systems can considerably reduce a building’s electricity consumption and also significantly improve the quality of light in an indoor environment.

1.1 IMPORTANCE OF DAYLIGHT

            Evidence that daylight is desirable can be found in research as well as in observations of human behaviour and the arrangement of office space. Windows that admit daylight in buildings are essential for the view and connection they provide with the outdoors. Daylight is also necessary for its quality, spectral composition, and variability. A review of peoples’ reactions to indoor environments suggests that daylight is desired because it fulfils two fundamental human requirements: to be able to see both a task and space well and to experience some environmental stimulation [Boyce 1998]. Working long-term in electric lighting is believed to be deleterious to health; working by daylight is believed to result in less stress and discomfort. Daylight provides high illuminance and permits excellent colour discrimination and colour rendering. These two properties mean that daylight provides the condition for good vision. However, daylight can also produce uncomfortable solar glare and very high luminance reflections on display screens, both of which interfere with good vision. Thus, the effect of daylight on the performance of tasks depends on how the daylight is delivered. All of these factors need to be considered in daylighting design for buildings. Daylight strategies and systems have not always lived up to their promise as energy efficiency strategies that enhance occupant comfort and performance. One reason is the lack of appropriate, low-cost, high-performance daylighting systems, simple tools to predict the performance of these advanced daylight strategies, and techniques to integrate daylight planning into the building design process. Common barriers that have hindered the integration of daylight in buildings in the past are:

• Lack of knowledge regarding the performance of advanced daylighting systems and lighting control strategies,
• Lack of appropriate, user-friendly daylighting design tools, and
• Lack of evidence of the advantages of daylighting in buildings. The barriers, identified at the beginning of the International Energy Agency (IEA) Solar Heating and Cooling (SHC).

Daylighting of Buildings were resolved by coordinated tasks that covered three broad areas:

1) assessment of the performance of systems and lighting control strategies,

2) development of integrated design tools, and

3) case studies to provide evidence of daylight performance in actual buildings. To remedy the lack of information about the performance of advanced daylighting systems, specified systems were assessed using standard monitoring procedures in test rooms in actual buildings, and using scale models under artificial skies. Parameters to measure both quantities (e.g., illuminance and luminance) and quality (e.g., visual comfort and acceptability) of daylight were determined prior to testing. This sourcebook describes the systems tested, the results of the assessments, and the appropriate application of the results. On the whole, the study’s results indicate that, when appropriately located, the majority of systems tested improved daylighting performance in perimeter building zones relative to the performance of conventional windows. The daylighting of buildings is essentially a systems integration challenge for a multidisciplinary design team, involving building siting and orientation and the design optimization of fenestration, lighting and control systems.

1.2 DAYLIGHT IN BUILDING DESIGN

For centuries, daylight was the only efficient source of light available. The architecture was dominated by the goal of spanning wide spaces and creating openings large enough to distribute daylight to building interiors. Efficient artificial light sources and fully glazed facades have liberated designers from these constraints of the past. Advanced daylighting systems and control strategies are another step forward in providing daylit, user-friendly, energy-efficient building environments. These systems need to be integrated into a building’s overall architectural strategy and incorporated into the design process from its earliest stages. This chapter outlines the design considerations associated with enhancing a building’s daylight utilization while achieving maximum energy efficiency and user acceptance.

Daylighting strategies and architectural design strategies are inseparable. Daylight not only replaces artificial lighting, reducing lighting energy use but also influences both heating and cooling loads. Planning for daylight, therefore, involves integrating the perspectives and requirements of various specialities and professionals. Daylighting design starts with the selection of a building site and continues as long as the building is occupied. Daylighting planning has different objectives at each stage of building design:

• Conceptual Design: As the building scheme is being created, daylighting design influences and/or is influenced by basic decisions about the building’s shape, proportions, and apertures, as well as about the integration and the role of building systems.
• Design Phase: As the building design evolves, daylighting strategies must be developed for different parts of the building. The design of facades and interior finishing, and the selection and integration of systems and services (including artificial lighting), are all related to the building’s daylighting plan.
• Final/Construction Planning: The selection of materials and products is affected by the building’s daylighting strategy; final details of the daylighting scheme must be worked out when construction plans are created.
• Commissioning and Post-Occupancy: Once the building is constructed, lighting controls must be calibrated, and ongoing operation and maintenance of the system begin.

1.2.1. Daylight Availability

All daylighting strategies make use of the luminance distribution from the sun, sky, buildings, and ground. Daylight strategies depend on the availability of natural light, which is determined by the latitude of the building site and the conditions immediately surrounding the building, e.g., the presence of obstructions. Daylighting strategies are also affected by climate; thus, the identification of seasonal, prevailing climate conditions, particularly ambient temperatures and sunshine probability, is a basic step in daylight design. Studying both climate and daylight availability at a construction site is key to understanding the operating conditions of the building’s facade. The daylighting design solution for the building should address all of these operating conditions. There are several sources of information on daylight availability [Dumortier, 1995]. For example, daylight availability data has been monitored every minute at more than 50 stations worldwide since 1991 and has also been monitored in the Meteosat satellite every half hour from 1996–1997 (under beta testing). High latitudes have distinct summer and winter conditions; the seasonal variation of daylight levels is less apparent at low latitudes. At high latitudes where winter daylight levels are low, designers usually aim to maximize daylight penetration in a building; redirection of daylight into buildings from the brightest regions of the sky is an appropriate strategy at these latitudes. By contrast, in the tropics where daylight levels are high throughout the year, the design emphasis is usually on preventing overheating by restricting the amount of daylight entering the building. The obstruction of large parts of the sky, especially of areas near the zenith, and the admission of daylight only from lower parts of the sky or of indirect light reflected from the ground are useful strategies in tropical regions. Daylight availability strongly depends not only on the latitude but also on a building’s orientation; each orientation will require a different design emphasis. Study of vernacular architecture and past successful daylighting designs is a good way to understand the relationship between climate and building design.

1.2.2 The Building Site and Obstructions

At a construction site, the sky is usually obstructed to some extent by surrounding buildings and vegetation Studying the obstructions at a construction site tells a designer about the daylight potential of the building’s facades and allows him or her to shape the building and to allocate floor areas with respect to daylight availability. In many cases, buildings are self-obstructing, so building design and obstruction studies become interconnected. Local zoning regulations limit a building’s design (e.g., building size, height, etc.) and the impact a new building can have on surrounding, existing buildings. The latter restrictions have their origins in fire protection, imposing minimum distances between neighbouring buildings to prevent the fire from spreading. These regulations evolved into legislation to protect the right to daylight, originally drafted (as early as 1792) when powerful sources of artificial light were unknown or unavailable to the majority of the population, and the availability of daylight was essential in building interiors. In selecting daylighting strategies, a designer must take into account the degree to which the new building will create an obstruction for existing buildings, reducing their access to daylight, and/or will reflect sunlight that might cause glare at the street level or increase thermal loads in neighbouring buildings. Zoning regulations and floor area indexes that regulate the extent of urban density also affect the daylighting design. The aim of maximizing floor area in order to get the best economic return from a new building may conflict with the design goal of providing interior daylight. Several methods and tools are available to analyze obstructions. The basic approaches are:

• plotting the “no-sky line” on the work plane of a selected space; the no-sky line divides points on the work plane that can and cannot “see” the sky ;
• examining obstructions from one specific viewpoint by projecting the sun’s course or a daylight availability chart on a representation of the building site
• computing the amount of incident daylight and radiation for specific locations and orientations on the site, or • projecting shadows that will fall on the facade or ground when the sun is in specific positions; this approach gives an overview of the availability of sunlight at the site. For heavily obstructed facades, daylight-redirecting systems can improve the distribution of light to interior spaces. Glass prisms have been used for this purpose for more than a hundred years; today a range of systems can be used, including holographic elements, laser-cut panels, and anidolic elements.

1.2.3. Building Schemes and Building Types

Commonly encountered constraints on different building types over the years have resulted in typical building shapes, and design schemes for standard types of building use. These schemes generally incorporate daylighting strategies from which designers can learn. Daylight design and building design can merge to different degrees. In some buildings, such as churches, the daylighting strategy and the building design scheme are almost identical; in buildings where the organization of floor areas is complex, daylight is treated as one design issue among a host of others. The more that daylight is the generating factor for a design, the more the daylighting strategy is an architectural strategy. Figure 1.1 represents the common building designs.

Figure 1.1 Different building design

1.2.4 Day lightning strategies for rooms

            The aims of room daylighting are to adequately illuminate visual tasks, to create an attractive visual environment, and to save electrical energy as represented in figure 1.2. Both the building design scheme and the application of systems play roles in meeting these goals. The performance of a daylighting strategy for rooms depends on:

• daylight availability on the building envelope which determines the potential to daylight space;
• physical and geometrical properties of window(s), and how windows are used to exploit and respond to available daylight;
• physical and geometrical properties of the space.

Figure 1.2 Day lightning strategies for rooms

1.2.5 Function of Windows

The old definition of a window as an aperture in an opaque envelope is no longer strictly applicable. Innovations such as fully glazed skeleton structures and double-skin facades defy the scope of this definition. Nevertheless, we will use the term “window” to analyze daylighting strategies. Windows have several functions, which vary depending on the individual design case. One key function of a window is to provide a view to the outside. View plays an important role in an occupant’s appraisal of the interior environment, even if the exterior environment is not especially attractive. The size and position of windows, window frames, and other elements of the facade need to be considered carefully in relation to the eye level of building occupants. Daylighting systems can affect the view to the outside. If an outdoor view is a priority in a daylighting design, visual contact with the exterior has to be maintained under all facade operating conditions. Advanced daylight strategies, therefore, often allocate different functions to different areas of the facade or to different facades. View windows than can be preserved without being compromised by other functions. Daylighting is one of the main functions of windows. The window design determines the distribution of daylight to space. Windows chosen solely for their architectural design features may perform satisfactorily in many cases. For dwellings and other buildings that have relatively minimal visual requirements, application of advanced daylighting systems is not usually appropriate. Advanced daylighting systems can be useful in cases where:

• difficult tasks are performed, and a high degree of control over the visual environment is required;
• the building’s geometry is complex, e.g., there are heavily obstructed facades or deep rooms;
• control of thermal loads is required (adjustable solar shading can be an effective strategy in this case). Daylighting is inseparably linked to solar gain. In some design cases, added solar gains from daylighting might be welcome; in other cases, heat gain must be controlled. If solar gains are desirable, windows are a good way to provide them. In general, the goal of building design is to reduce cooling loads. There are a number of ways to control solar gains from windows and facades; the simplest method is the direct gain approach, where a shading system simultaneously controls the visual and thermal environments. More advanced techniques, such as collector windows and double-skin facades, allow some degree of separate control over the thermal and visual environments. In passive solar architectural concepts, solar gains are controlled by the orientation and the application of shading systems as a function of the sun’s position. The operability of windows needs to be considered when daylighting systems are selected. Shading systems located in the windowpane do not work properly when the window is open; if daylight-redirecting systems are attached to the window, the window’s operation will have an impact on the systems’ performance. Operable windows also often serve as fire escapes. The impact of fire balconies on daylight performance needs to be considered. Glazed areas are an interface between exterior and interior; therefore, windows involve a number of design considerations. Aside from the above-mentioned primary functions, the following issues are especially important for glazed areas:
• glare,
• privacy/screening of view,
• protection from burglary.

1.2.5.1 Design Strategies for Windows

A window system must address the range of a building’s exterior conditions to fulfil the range of interior requirements. The placement and sizing of windows are among the most powerful features of architectural design for daylight. Because the design of windows has a decisive effect on the potential daylight and thermal performance of adjacent spaces, it needs to be checked very carefully [O’Connor et al. 1997]. The LT (Light-Thermal) method, which was developed for typical climates in the European Union, allows the estimation of energy consumption for heating, lighting, and cooling as a function of glazing ratio [Baker and Steemers 2000]. Simple design tools allow a quick evaluation of window design and room geometry. Windows are almost always exposed to the sky; daylighting systems can adapt windows to changing sky conditions and transmit or reflect daylight as a function of incident angle. Daylighting systems are primarily used for solar shading, protection from glare, and redirection of daylight. Whether or not daylighting systems are required to support the performance of window systems, and which system or systems are appropriate, are key decisions in the design process? The adjustment of daylighting strategies to specific sources of skylight is an important characteristic of daylighting strategies.

1.Strategies for Skylight

Strategies for a diffuse skylight can be designed for either clear or cloudy skies; however, the most significant characteristic of these strategies is how they deal with direct sunlight. Solar shading always is an issue for daylighting except on north-oriented facades (in the northern hemisphere). If solar shading is only of minor importance as a result of orientation and obstructions, a system to protect from glare can be used for solar shading as well. Solar shading and glare protection are different functions that require individual design consideration. Solar shading is a thermal function that primarily protects from direct sunlight, and glare protection is a visual function that moderates high luminances in the visual field. Systems to protect from glare address not only direct sunlight but skylight and reflected sunlight as well.

2.Strategies for Cloudy Skies

Daylighting strategies designed for diffuse skylight in predominantly cloudy conditions aim to distribute skylight to interior spaces when the direct sun is not present. In this case, windows and roof lights are designed to bring daylight into rooms under cloudy sky conditions, so windows will be relatively large and located high on the walls. Under sunny conditions, these large openings are a weak point, causing overheating and glare. Therefore, systems that provide sun shading and glare protection are an indispensable part of this strategy. Depending on the design strategy, various shading systems that transmit either a diffuse skylight or direct sunlight may be applicable in this case. To avoid decreasing daylight levels under overcast sky conditions, moveable systems are usually applied. Some innovative daylighting systems are designed to enhance daylight penetration under cloudy sky conditions. Some of these systems, such as anidolic systems or light shelves, can control sunlight to some extent. The application of simple architectural measures, such as reflective sills, is another opportunity to enhance daylight penetration, but the design of the window itself is the main influence on the performance of this type of strategy under cloudy conditions.

3.Strategies for Clear Skies

In contrast to daylighting strategies for cloudy skies, strategies that diffuse skylight in climates where clear skies predominate must address direct sunlight at all times. Shading of direct sunlight is, therefore, part of the continuous operating mode of this strategy. Openings for clear sky strategies do not need to be sized for the low daylight levels of overcast skies. Shading systems that allow the window to depend primarily on diffuse skylight are applicable in this case.

4.Direct Sunlight

Strategies for sunlight and diffuse skylight are quite different. Direct sunlight is so bright that the amount of incident sunlight falling on a small aperture is sufficient to provide adequate daylight levels in large interior spaces. Beam daylighting strategies are applicable if the sunshine probability is high. Since sunlight is a parallel source, direct sunlight can be easily guided and piped. Optical systems for direct light guiding and systems for light transport are applicable in this case .  Apertures designed for beam daylighting do not usually provide a view to the outside and should, therefore, be combined with other view openings. Because beam daylighting requires only small apertures, it can be applied as an added strategy in an approach that otherwise focuses on cloudy skies.

5.Design strategies of a daylighting systems.

            The application of daylighting systems is only one constituent of a daylighting strategy. Although a poor selection of systems can spoil the performance of a building with good daylight potential, a sound selection cannot compensate for errors and omissions in previous design stages. To select a system, the designer must understand:

• the function of the window or other opening(s),
• the function of the system, and
• the interplay of the system with other systems. A reasonable selection of systems should reduce the negative effects of windows and enhance daylight performance without interfering with other desirable effects of windows for all design cases (all seasons and sky conditions). Daylighting systems can be categorized by many characteristics. When selecting a system, the designer must be aware of all of its properties. Function and performance parameters have the most pronounced effect on performance, but costs and details related to the skin of the building are also important. As for many decision within the design process, there exists no definite procedure on how to select a daylighting system. The ultimate criterion is the performance of the overall design solution. Windows and roof lights have different roles in a daylighting strategy. The ambience of spaces receiving skylight is completely different from that of spaces receiving sidelight. Rooflights are usually not designed for a view to the outside; therefore, obstructing elements such as deep light shafts or non-transparent daylight systems can be applied in rooflight design. The control of glare with such systems is much easier than with sidelights designs, which must provide occupants with a view to the outside. Solar shading is a crucial issue with roof lighting. One design strategy for roof lighting in hot sunny climates is to use a very small aperture and to apply innovative daylighting systems to distribute the light homogeneously in the space (→ Waterford School, International Centre for Desert Architecture). In classrooms of the Park Ridge Primary School in the sunny but temperate climate of Melbourne in southern Australia, tunnel lights are used to exclude direct sunlight and to distribute skylight to space (→ Park Ridge Primary School). Shading systems for roof lights, such as sun-protecting mirror elements, prismatic panels, and directional selective shading systems using holographic optical elements can be applied to large glazed roof areas in higher latitudes. When situated in the windowpane, these systems are protected from dust and require little maintenance. These systems need to be adjusted to the individual application. Windows need protection from glare and solar shading in order to create acceptable interior conditions. The redirection of daylight can save energy but is not an indispensable function. The view to the outside is not a function of a daylighting system but a primary function of the window itself; the impact of daylighting systems on the view to the outside needs to be considered carefully.

1.3 PERFORMANCE PARAMETERS

            Performance parameters characterize a daylighting system within the context of a specific building application and can be used to determine whether a system should be used to achieve the design objectives. Parameters include visual performance and comfort, building energy use, economy, and systems integration. The primary energy-related design objectives of a daylighting system are to provide usable daylight for a particular climate or building type for a significant part of the year, which allows electric lighting to be offset by natural daylight and cooling and heating loads to be reduced. Conventional window and skylight solutions meet some of these needs; this guide focuses on new technologies and solutions that extend performance beyond that of conventional solutions. The functions of these new design solutions can be summarised as follows:

• provide usable daylight at greater depths from the window wall than is possible with conventional designs,
• increase usable daylight for climates with predominantly overcast skies,
• increase usable daylight for very sunny climates where control of direct sun is required,
• increase usable daylight for windows that are blocked by exterior obstructions and therefore have a restricted view of the sky, and
• transport usable daylight to windowless spaces. The term “usable daylight” encompasses objective and subjective measures for visibility and comfort:
• higher illuminance levels, often at greater depths from the daylight opening, than provided by conventional solutions under both cloudy and clear sky conditions,
• greater uniformity of light distribution,
• reduction of glare and cooling loads by controlling direct sun without compromising daylight admission. An objective evaluation of an innovative system requires a definition of performance parameters. In addition, the evaluation depends on defining baseline conditions against which the performance should be compared. The performance parameters are summarized in the table below. In the following sections, these terms are defined within the context of the general field of lighting, and their respective ranges of acceptable or target values are given, if available. A discussion follows concerning how these terms apply to the unique, light-redirecting daylighting systems covered in this book. Many existing performance parameters are not directly translatable to advanced daylighting either because the parameters were developed for static electric lighting sources, or because research has been insufficient to develop adequate, robust performance models. These issues are also briefly discussed. Table 1.1 represents the performance parameters in the building daylighting.

Table 1.1 performance parameters

1.3.1 Visual function parameters

Visual function parameters are used to determine whether a given lighting condition permits sight or visibility and are directly related to the physiology of the eye. Generally, good visibility is defined by an adequate quantity of light for the expected visual task, uniform distribution of illuminance and luminance, sufficient directionality to model three-dimensional objects and surfaces (direction of incident light from the side or from above), the absence of glare, and sufficient spectral content to render colours accurately when required.

1. Illuminance

Guidelines for electric lighting have defined ranges of “design” illuminance levels based on task, viewer’s age, speed and accuracy requirements, and task background reflectance [IES 1993a, CIE-29.2 1986]. For daylighting, the total energy balance between lighting and thermal loads (i.e., from solar heat gains) is an added consideration. For paper-based tasks such as reading and writing, satisfactory task illuminance levels can exceed recommended electric lighting levels by factors of two or more if there is no glare and if the associated heat gains have a minimal mechanical system energy impact (especially in cooling-dominated climates). For computer-based or other self-illuminating tasks characterized by low luminance values larger the number of hours per year that a system is able to meet but not grossly exceed the design illuminance level, the more successful the design. For systems designed to redirect light to greater depths than is possible with conventional technologies, “good” systems are those that can meet the design illuminance level at greater depths and for a greater percentage of the year than conventional window systems. As a rule of thumb, conventional windows can daylight a room to a depth of 1.5 to two times the height of the window above the floor. Some daylighting systems are designed to achieve light redirection to depths of two or more times the window height for a greater percentage of the year than is possible with conventional designs. Task locations are often ambiguous or change frequently, so an evaluation is usually conducted at representative locations within a space.

2. Distribution

The distribution of illuminance and luminance is a measure of how lighting varies from point to point across a plane or surface. For good visibility, some degree of uniformity across the task plane is desirable. Poor visibility and visual discomfort may result if the eye is forced to adapt too quickly to a wide range of light levels. Illuminance and luminance ratios such as maximum-to-average or average-to-minimum are used to quantify lighting uniformity and are typically measured across a horizontal work plane at the height of 0.8 m above the floor for paper or reading tasks. For office lighting, for example, the ANSI/IESNA RP-1 guidelines set maximum contrast ratios among all task, background, and remote surfaces within the occupant’s field of view :

• variation in luminance across the immediate task (within one’s central or Programa vision) should be kept to a maximum of 2.5:1 to 3:1;
• variation in luminance between the task and background (central or ergorama vision; e.g., black letters on a white background) is permitted, typically 3:1;
• greater variation is permitted between the task and remote surfaces (panorama view; e.g., walls, ceiling, and floor), typically 10:1, but the design must meet additional guidelines for glare (e.g., 20:1 to 40:1).

A systematic evaluation of daylighting systems is complicated by a number of factors, however:

• the sun is a variable-position light source, so the sheer number of conditions one must evaluate is large;
• the task location is often ambiguous, requiring one to either consider all views within the space or to select several representative task locations;
• if the direct sun is not excluded or is redirected, continuous surface luminance maps may be the only method to determine the location, size, and intensity of bright areas of sunlight;
• the luminance of exterior obstructions (e.g., opposing semi-reflective buildings) or the ground (e.g., snow) varies with task location and solar conditions; • occupants may accept much greater luminance variations when spaces are lit by daylight than when they are artificially lit, which further complicates comparisons. At a minimum, the illuminance profile throughout the space can be measured or simulated, and contrast ratios can be computed. This profile typically illustrates how daylighting systems achieve more uniformity throughout the space than conventional windows.

3. Glare Disability

Glare Disability glare is caused when intraocular light scatters occurs within the eye, the contrast in the retinal image is reduced (typically at low light levels), and vision is partly or totally impeded (e.g., when the eye is confronted by headlights from oncoming automobiles). With windows and daylighting systems, which are large-area light sources, disability glare can at times be significant. Experts agree that this apparent reduction, in contrast, is affected by the total intensity of the glare source — not just by the brightness or area alone. However, there are no known satisfactory models to predict and evaluate this condition. A daylighting design should be evaluated to determine whether there are strategies or features that enable occupants to control situations where the eye is forced to adapt to different brightness regions within the field of view. Discomfort Glare Discomfort glare is a sensation of annoyance caused by high or non-uniform distributions of brightness in the field of view. The physiological mechanisms of discomfort glare are not well understood; an assessment of discomfort glare is based on size, luminance, and a number of glare sources, source-task-eye geometry (or glare source locations within the field of view), and background luminance. The Daylighting Glare Index (DGI) is used to indicate the subjective response to a large-area glare source and can be calculated for a person facing the window or the sidewall at various distances from the window wall. However, the DGI can only be used for large areas with a nearly homogeneous luminance distribution, e.g., a view to a uniform sky luminance through a window. When the luminance distribution from daylighting systems varies substantially, the DGI cannot be used. To simplify the analysis, several rules of thumb can be applied to evaluate daylighting systems.

4.Geometry.

Glare sources must be kept out of the line of sight. For a horizontal view angle, sources within 50-90° above the horizontal can cause high-angle or overhead glare. They are veiling Reflections Visual discomfort or glare results from bright reflections off shiny surfaces. These veiling reflections reduce contrast and impair visibility. Daylighting systems can reduce or eliminate veiling reflections by controlling direct sun and luminance levels within the offending zone or the area viewed by the task surface.

 5.Direction

For some tasks, sufficient directionality is required to model and evaluate three-dimensional objects and surfaces. The greater the amount of diffuse light, the less shadowing occurs, reducing an occupant’s ability to evaluate the depth, shape, and texture of a surface. A balance between diffuse and directional light enables an occupant to evaluate the smoothness, nap, grain, iridescence, specularity, and other properties of a surface. For horizontal tasks, side lighting from daylighting systems can enable better visibility than lighting from an overhead electric lighting installation. There are no standard performance parameters to evaluate the direction and diffusion of light. Direct sunlight is typically directional with sufficient diffuse light from the sky to balance out the contrast of a three-dimensional object. Daylighting systems that rely on skylight will typically produce diffuse Omni-directional light. Some daylighting systems using non-imaging optics (e.g., anidolic systems) can redirect diffuse daylight in the same way a light projector does, so some directional effects appear even in diffuse daylight.

1.4 DAYLIGHTING SYSTEMS

Daylighting Systems with Shading Two types of daylighting systems with shading are covered: systems that rely primarily on the diffuse skylight and reject direct sunlight, and systems that use primarily direct sunlight, sending it onto the ceiling or to locations above eye height. Shading systems are designed for solar shading as well as daylighting; they may address other daylighting issues as well, such as protection from glare and redirection of direct or diffuse daylight. The use of conventional solar shading systems, such as pull-down shades, often significantly reduces the admission of daylight to a room. To increase daylight while providing shading, advanced systems have been developed that both protect the area near the window from direct sunlight and send direct and/or diffuse daylight into the interior of the room. Daylighting Systems Without Shading Daylighting systems without shading are designed primarily to redirect daylight to areas away from a window or skylight opening. They may or may not block direct sunlight. These systems can be broken down into four categories: Diffuse Light-Guiding Systems redirect daylight from specific areas of the sky vault to the interior of the room. Under overcast sky conditions, the area around the sky zenith is much brighter than the area close to the horizon. For sites with tall external obstructions (typical in dense urban environments), the upper portion of the sky may be the only source of daylight. Light-guiding systems can improve daylight utilization in these situations. Direct Light-Guiding Systems send direct sunlight to the interior of the room without the secondary effects of glare and overheating. Light-Scattering or Diffusing Systems are used in skylit or top-lit apertures to produce even daylight distribution. If these systems are used in vertical window apertures, serious glare will result. Light Transport Systems collect and transport sunlight over long distances to the core of a building via fibre-optics or light pipes.

1.5 BENEFITS OF DAY LIGHTNING

            We know that appropriate light signals during the day and darkness at night are critical in maintaining key aspects of our overall health. In order to align our body clock, morning light is the most important signal for entrainment. Light in the morning also increases our levels of alertness, allowing increased performance at the beginning of the day. From mid-morning to early evening, high levels of daylight, allow us to regulate our sleep/wake timing and levels of alertness; whereas reduced light levels in the evening and a dark room with blackout promote sleep at night. The inability to provide building occupants with a good overall lighting environment can have a subsequent impact on health and place a substantial burden on the individual, society and the broader economy.

1.Performance and productivity

            Bright lighting is generally believed to make people more alert, and well-daylit spaces are generally perceived by occupants to be “better” than dim, gloomy ones. Daylighting has been associated with improved mood, enhanced morale, less fatigue, and reduced eyestrain. Many studies show that the performance and productivity of workers in the office, industrial, and retail environments can increase with the quality of light. Companies have recorded an increase in productivity of their employees of about 15% after moving to a new building with better daylight conditions which resulted in considerable financial gains. Another study demonstrated that greater satisfaction with lighting conditions (both daylight and electric lighting) contributed to environmental satisfaction, which, in turn, led to greater job satisfaction. Studies also show that daylit environments lead to more effective learning. It was found that students in classrooms with the most window area or daylighting produced 7% to 18% higher scores on the standardized tests than those with the least window area or daylight.

2.Impact of daylight in hospital rooms

            There is some evidence that daylight exposure can affect postoperative outcomes in patients and, consequently, that daylight should be a consideration in hospital design. Ulrich (1984) reported that hospital patients with a view of green spaces, as opposed to those with a view of a blank brick wall, recovered more quickly from surgery and required less post-operative pain medication. Beauchemin and Hays (1998) found that patients on the sunnier side of a cardiac intensive care ward showed lower mortality rates than those on the less-sunny side. Another study determined that sunlight exposure was associated with both improved subjective assessment of the patients and also reduced levels of analgesic medication routinely administered to control postoperative pain (Walch et al., 2005). The importance of the amount of daylight in a patient’s room indicates an impact on patients’ length of stay; coronary artery bypass graft surgery patients’ length of stay in hospital was reduced by 7.3 hours per 100 lx increase of daylight (Joarder and Price, 2013).

3.Preventional of Seasonal Affective Disorder

Seasonal Affective Disorder is a depression-related illness linked to the availability and change of outdoor light in the winter. Reports suggest that 0.4% to 9.7% of the world’s population may suffer from SAD, with up to three times that number is having signs of the affliction (called sub-syndromal SAD (or S-SAD) without being classified as major depression (primarily in Northern America and Northern Europe) (Rosen et al., 1990). Light therapy with exposure levels at the eye of between 2500 lux (for 2 hours) or 10 000 lux (for 30 minutes) has shown to be an effective cure against SAD (Sloane, 2008). Exposure to daylight outdoors (~ 1000 lux) can also reduce SAD symptoms (Wirz-Justice et al., 1996). So, as seasonal mood disturbance is relatively common, the amount of daylight in our homes or workplaces can be of considerable significance – though the effective value of daylight will depend on the architectural design of a room and the facade (Pechacek et al., 2008). Light therapy can also be used to treat other depression-related symptoms (e.g. non-seasonal depression, premenstrual, bulimia).

4.Energy savings for daylighting

            Another benefit of using daylighting for ambient and/or task illuminance in a space is that it can save energy by reducing the need for electric lighting. Several studies in office buildings have recorded the energy savings for electric lighting from using daylight in the range of 20-60% (Galasiu, 2007), but it depends on the lighting control system used, how well space is daylit during occupied hours and the intended functions of the space. If no control system is installed, the occupant entering a space will often switch on the electric lights. Quite why occupants switch on or off the office lights is not always obvious, but it is even less obvious in a domestic setting, where demand for light is typically driven by human needs and wishes.

In non-domestic buildings, the official recommended illumination levels are defined for the spaces they illuminate. They are dependent on the type of space to be lit, and the functions within it and are based on both the functional efficiency of anticipated tasks performed in the spaces and visual comfort (IEA, 2006). Typically guidelines and recommendations for light levels exist for communal residential buildings but not for single-family houses.

Estimation of savings potential in domestic buildings requires a user profile and models for switching on/off the lights. In a study by Mardaljevic et al. (2012), the French RT 2005 model was used. They analyzed the potential for increased daylight provision for a house with or without skylight to save electric lighting energy at eight European locations. The study shows that increased daylight is estimated to reduce the need for artificial lighting by 16-20%, depending on the location and orientation of the house.

In LichtAktiv Haus in Germany, the electric lighting used in the kitchen and living room shows a significant tendency of being affected by the interior daylight level; the lights are typically switched on before sunrise and after sunset. There is a reasonable correlation between high daylight level and switching probability, while outside weather, the day of the week has less impact (e.g. family with children).

5.Environmental benefits

Increasing use of natural resources, such as daylight and air, in our buildings, through constructive use of windows in the facades and roofs, can influence our dependency on fossil fuels as well as reduce combustion of greenhouse gases. Lighting is one of the largest consumers of electricity and one of the biggest causes of energy-related greenhouse gas emissions. The amount of electricity consumed by lighting is almost the same as that produced from all gas fired generation and about 15% more than that produced by either hydro or nuclear power. Indoor illumination of tertiary-sector buildings uses the largest proportion of lighting electrical energy, comprising as much as the residential and industrial sectors combined. On average, lighting accounts for 34% of tertiary-sector electricity consumption and 14% of residential consumption in OECD countries. In non-OECD countries these shares are usually higher (IEA, 2006).

1.6 MAXIMIZING NATURAL LIGHTING IN BUILDING DESIGNS

More and more developers are looking for sustainable solutions for offices, retail buildings, schools, and other commercial enterprises, and lighting is an important component of sustainable design. When designing a new structure or renovating an older one, consider the following ways to maximize natural lighting:

1.6.1 Proper glazing

A building with a lot of windows will allow a lot of light in. However, when sunlight comes directly through windows that don’t have the right type of glazing, it can create unpleasant glare or hotspots that are too bright. When this happens, building occupants typically draw the shades and turn on electric lights, defeating the purpose of your daylighting solution. However, windows with the right type of glazing and shading can reduce this glare and prevent solar heat gain while still allowing natural light to pass through.

1.6.2 Building layout

In a multi-story building that uses windows for natural lighting on lower levels, the amount of light that enters a space can be limited, so it’s important to consider how the space will be used. For example, placing offices and common spaces around the perimeter nearest the windows, and transitional spaces like bathrooms and supply rooms in the center of the space will allow occupants to get the most from the natural light.

1.6.3 Smart skylights

For upper floors or single-story structures, skylights can provide some of the best natural light throughout the entire area. However, there are some important considerations when selecting an industrial skylight. Just as a window with poor glazing will defeat the purpose of your natural lighting strategy, so will a poorly selected skylight. Traditional skylights create hotspots and can create solar heat gain, impacting the cooling load of the building. While more advanced skylights, such as tubular and prismatic, have some benefits, they only provide natural lighting for a limited period of time during the day. Solar tracking skylights deliver the most light and can recoup the costs in two and a half to four years, offering the quickest return on investment of any skylight model available.

Ciralight SunTrackers are designed to capture natural light throughout the entire day. With a solar-powered GPS controller and a dynamic mirror array that harnesses sunlight no matter where the sun is in the sky, SunTrackers can deliver more than ten hours of natural lighting per day.

1.7 RESEARCH OBJECTIVES

The present research has been carried out in three stages. The main objectives of the stages 1, 2 and 3 are stated below:

• To implement a novel method light solve approach daylight integration to school building and assessing daylight exploitation performance.
• Optimal investigation of daylighting and energy efficiency in industrial building using energy efficient velux daylighting simulation.
• Assessment of daytime luminance and improvement of daylight feasibility using Google NET CNN.

The main intention was the improve the feasibility of the daylightning in the building .

1.8 RESEARCH PROBLEMS

Focusing on natural light enables you to create a space which feels much bigger and comfortable than its counter parts which are artificially lit. Natural light gives an extra edge to the colors present indoors by making it look more profound, natural, and far more pleasing. Lighting costs can be reduced by 20 to 80% through daylighting. More than a third of the energy used in the United States is consumed in buildings, and 25 to 40 % of that is used to run electric lights. The building architecture sometimes reduces the day lightning entry efficiency. Increase day lightning will reduce power consumption.

1.9 THESIS ORGANIZATIONS

                   Chapter 1: Introduction: In this chapter, some overviews including introduction to building design on daylightning , objectives, and  benefits of daylightning was presented.

                   Chapter 2: Literature Survey: Some literature reviews, reviews of contribution of other researchers and related works regarding this work are depicted.

                   Chapter 3: Research Methodology: In this chapter, a novel unified technique was proposed for the assessing of the daylight in the building

                   Chapter 4: In this chapter aims to evaluate the daylight availability in an industrial building under a fixed level of orientation and design using velux daylight simulation.

Chapter 5: In this chapter illustrates how the CNNs are incorporated into a case study that explores plans for a school building corridor                                                

                    Chapter 6: Results and Discussion: This chapter provides the detailed analysis of performance estimation of the proposed techniques.

                     Chapter 7: Conclusion and future work: This chapter concludes with important results that have been obtained from the proposed work. This chapter also suggests further improvements to further increase the accuracy

1.10 SUMMARY

This chapter presents about the introduction about the importance of the daylightning in buildings. This chapter implicitly explains the need of detection of the novel technique for improving the characteristics feasibility of daylightning in buildings. From this chapter anyone can read and understand the functionalities of the entire thesis concept in a better manner.