Daylighting

What is Daylighting in Architecture

Daylight is an important component of architecture in its historical, theoretical, and technical conceptions, with the ability to inspire people and illuminate design elements. It is the combination of all the direct and indirect sunlight during the day. Daylight is a necessary element in a building’s design; we can’t just rely on artificial light. Daylighting in buildings have several benefits over artificial lighting, and we need to use it as much as possible in any space. Daylighting in buildings can be employed to conserve energy and enhance visibility inside any space. Making extensive use of daylight frequently necessitates significant trade-offs, as well as design and building operation decisions. [1]

Specific goals related to the daylighting of buildings

• Design to achieve significant, useful amounts of daylight in all feasible areas.
• Distribute daylight fairly evenly, with no significant dark spots (although variation within the visible range is acceptable and can provide desirable relief).
• Allowing direct sunlight into the building interior may cause visual discomfort (excessive brightness differences) or visual disability (glare). Examine the design for all potential sun penetration angles.
• Electric lighting should include daylight-sensitive controls so that it can be dimmed or turned off when not required.
• The site, climate, and neighborhood are all taken into account when designing the architecture for daylighting, which also includes building geometry, surface materials and finish treatments, apertures, and windows.
• The technique of designing for daylighting in buildings entails using reflection, diffusion, and redirection to make such daylight-source illumination comfortable and usable. [1]

Source of Daylight in Buildings

Windows:- Windows are the main source of daylight inside any space. Naturally, bigger windows admit more daylight. But the height of the windows is the more significant factor in getting the daylight deep into the interior. The higher the space, the farther will be the daylight penetration

Daylighting in buildings can be quite easily achieved to a depth of about 15 ft. (4.5 m) inward from the aperture; with windows open to a high ceiling, about 20 ft. (6 m) inward from the aperture.

Light shelves:-  A light shelf is a horizontal plane placed below the top of a window, usually just above door height, allowing light to be reflected from its upper surface to the ceiling level. The light shelf can be placed entirely outside or in a combination of outside and inside. When the top surface of the light shelf is exposed to direct sunlight, it reflects daylight onto the interior ceiling and thus extends light farther into the room.

Skylights:- Even under an overcast sky, the illumination falling on the horizontal plane of the roof may be many times greater than that which strikes the vertical plane of a window. To allow the eye to adjust to the bright sky lighting source, some shadowing and reflecting surfaces are needed.

Skylights reduce energy consumption by reducing the need for electric lighting and heat in winters.

Clerestories:- Clerestories have many of the attributes of skylights except that they occur in the vertical rather than the horizontal plane and, therefore, are exposed to less quantity of direct daylight than skylights.

A clerestory, when combined with an interior reflector or light shelf, can bounce large amounts of direct sunlight against the ceiling, providing significant levels of illumination for the tasks below. [1]

Criteria for Daylighting design

Sky conditions

In daylighting design, three types of sky conditions are typically considered:

• Clear sky:- which provides a relatively steady source of low-intensity light with direct sun of high intensity. For buildings designed for climates with prevailing clear skies, solar control (sun-shading) is generally required and can be reliably dimensioned, depending on the requisites of under heated versus overheated conditions. Window apertures in hot arid climates (such as a desert location) can be very small and use reflected light to protect the interior from direct sun and glare while still providing high levels of illumination.
• Overcast sky:- which may be a very dark under dark clouds, or which may be very bright and “hazy,” low level lighting, but diffusely cast from the entire sky dome (that is, nearly omnidirectional). When viewed from inside a building, an overcast sky can be either excessively bright or quite dark. Fixed exterior sun control is generally not recommended in climates with prevailing cloudy skies because it increases darkness and shading under overcast conditions. Interior shades for glare control from all angles may be required.
• Partly cloudy:- sky can be considered a third type of sky from the standpoint of daylighting design, characterized by partial or intermittent clouds and by a blue background with bright, white clouds (oftentimes passing and changing rapidly), with direct sunshine penetrating off and on. Intensities on the ground can change rapidly. Passing clouds viewed from the interior can be exceedingly bright, causing glare and visual discomfort. In climates with such erratic weather, a combination of fixed and movable sun and light controls is advised. [1]

Site and building orientation

Consider the following site features:-

• The building’s location on the site should be such that daylight can reach the apertures without interference from nearby obstacles (such as tall buildings, mountains, or trees).
• Nearby highly reflective surfaces, such as glass-covered buildings, could cause excessive glare.
• Trees and shrubs on the property may provide shade and reduce interior sky glare.
• Ground surfaces are bright and can be used to reflect daylight into the interior (as much as 40% of interior daylight can come reflected from ground surfaces). Glare from reflecting surfaces such as the ground or window sills must be avoided. [1]

Intensity of daylight in different conditions

Devices that control daylight

• Louvers:- There are a variety of types of louvers for daylight control. They may be small, movable, and on the interior (such as Venetian blinds), or they may be large and fixed on the exterior as were commonly found on buildings.
• Venetian blind:- Venetian blinds can be adjusted to exclude direct sun but reflect its light to the ceiling where it will bounce into the interior areas, while still allowing a view of the exterior. Horizontal louvers and overhangs are most effective for high altitude sun such as on the south fenestration. Vertical louvers are most effective for low-altitude sun such as on the east and west facades. For situations where both high and low sun must be considered (southwest facade), “egg crate” louvers are often the most effective control.
• Glazing:– The most popular types of glazing materials include clear glass, tinted glass, and other glasses. Tinted glazing is recommended for use only when the primary source of interior light is from other locations (that is, skylights or electric lights) and the tinted glazing is used only for viewing out.

• Overhangs:- Overhangs on buildings can be very useful for sun and rain protection. Overhangs can also help to reduce the amount of bright sky visible from within the interior, though the effect is usually minor. [1]

Benefits of using daylighting in a buildings

• Aesthetics: the play of light from windows on surfaces and textures, casting interesting shadows; the endless variety of moods and appearances due to the movement of the sun.
• Psychological response: the sense of well-being associated with daylight and the sense of orientation that comes with being “connected” with the exterior.
• Health: improved resistance to infections, skin disorders, and cardiovascular impairment.
• Energy/Cost: reduction in electric use and related air conditioning load from electric lighting. [1]

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