DESIGN CONSIDERATIONS for DAYLIGHTING

Post 593 by Gautam Shah

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Daylighting is illuminating the interiors of built spaces with the sunlight, as available during the sun up period. This is controlled entry of natural light and diffuse skylight into a building to reduce electric lighting and saving energy. The ‘direct’ daylight arrives through openings like doors, windows, skylights and other gaps. Indirect daylight is brought in as Diffused sky light from surface reflectors or Transmitted light through tubes and other devices.

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Haveli Courtyard, Near begum Samru’s palace > Flickr image by Varun Shiv Kapur

Daylighting depends on the external conditions, such as the season of the year, climate, dust, fog or cloud cover, time of the day, terrain or surroundings. Daylight can be designed through buildings, size (spread or massing, depth, floor heights), form or shape, orientation, scheduling and location of tasks, configurations of openings, etc. It is closely linked to saving energy used for lighting during daytime. Daylight is substantially dependent on openings like doors and windows, and this help creates stimulating and natural environment.

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Chhatrapati Shivaji International Airport Mumbai Departure area > Wikipedia image by Nancy Beaton

Daylighting is dependent on external conditions. The season of the year determines not only the ‘sunshine’ days and brightness, but the direction (solar inclination) of the light. The climatic conditions govern if fenestrations can be kept fully open or closed. Local atmospheric conditions like dust, fog, cloud cover and pollution affect the intensity of daylight. Activities must be scheduled according to the diurnal cycle and positioned as per the available exposure. The surroundings’ factors, such as the terrain slopes, colour (of white sand beach fronts, green lawns or foliage, water bodies), and reflective capacities determine the brightness level of illumination.

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Sahara Town Ghadames Libya > Wikipedia image by Luca Galuzzi http://www.galuzzi.it

Daylighting and building design, have mutual dependence. The exposure of the face, surface area, perimeter and form of the buildings can be advantageously exploited for better gain of daylight.

Daylighting for energy saving must be conceived with a view to reduce the artificial illumination requirements of deep-set spaces, low height spaces, isolated interior entities like vestibules and corridors. A synergetic system to calibrate the electric illumination can be created for task-need and occupancy of the space, compensative distribution (elimination of glare-contrasts) and low heat output.

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High sill windows Abbaye d’Acey Jura France > Wikipedia image by Arnaud 25

Fenestrations and Daylighting are linked. Fenestration location (wall, skylights), height, shape and construction affect the daylighting. Fenestrations also serve the purpose of comfort (ventilation requirements such as heat gain-loss, air-moisture control, interior pollutant dilution, air movements) and view in-out, so must incorporate these requirements.

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Daylight used for illuminating interior spaces, exploits the ever-changing quality in terms of intensity, colour and direction of the light. The daylight-design, scatters the light over a wider extent, diffuses its intensity and subdues the strong directionality, alters the colour quality, and shifts the location of the source.

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Screening for daylight and view Wikipedia image by Margaret Bourke-White

Light intensity is a function of season, orientation and fenestration design. These are important considerations for siting an activity. Light intensity is perceived against the brightness level of the background scene or the surfaces. It can also be altered by illumination from other directions or additional artificial sources.

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Tony Rich Training Centre Uni of Essex Consistent illumination by skylight and support by electric light> Wikipedia image by Rwendland

Colour of the daylight as reflected sky component have small colour variations, except the occasional colour scattering at sun rise and set periods. Daylight received from reflected surfaces such as terrain, near by buildings and plants has a colour tinge. The colour of the glazing material, colour of the opening cover systems like Venetian blinds, curtains, overlay films, etc. side-surfaces of fenestration systems.

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Colours of the surroundings > Flickr image by Darron Birgenheier

Direction of the light is an important consideration for ingress or avoidance direct sunlight. North light (South light in S-hemisphere), are designed to access best natural illumination for industrial plants. East side facing openings allow ‘cool’ brightness in comparison to West faces.

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Darker surface does not equalize the light > Pixabay image

Scattering the light over a wider area achieves equal brightness by avoiding high-low contrast or patchy areas. This is done by multiple openings or by masking the opening with diffuser screens. Scattering is avoided where dramatic effects are intentionally created such as vestibules, entrance halls, etc. Equalization of illumination in space is also achieved by electronic sensors that activate electric illumination in required intensity.

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Taliesin West drafting studio illumination > Wikipedia image by Steven C. Price

Diffusing the intensity of light is resorted to reduce the high level of brightness on summer or clear sky afternoon periods. This is done by automatic masking devices or by baffles or louvers with apertures attuned to non-bright exposure-directions and schedules. Diffusers are also used to reduce the level of brightness in areas that act as transition spaces to darker environments such as auditoriums.

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Strong light source and contrast > Pixabay image (of woman by window)

Calibrating a strong sense directionality with illumination is necessary to reduce the dynamism of direct natural illumination. Architectural openings like doors and windows bring in variations of brightness (movement of clouds), shadows of moving objects (trees, vehicles, other traffic), and variations of colours into the interior spaces. This changeability is often an irritant for work areas like laboratories, libraries, bedrooms, etc. By sourcing the daylight from multiple directions, the illumination can be made static and multilateral.

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Contrast reduced by additional illumination from side openings >Window at the East end of Choir in Month of Feb, Wells Cathedral Somerset > Wikipedia image by IDS.photos from Tiverton, UK

Altering the colour quality where colour perception is important such as in surgical and pathological areas of hospitals, colour and dye manufacturing plants, film and media editing rooms. Here not only the colour must be neutral but consistent. This is achieved by avoiding light reflected from external sources, such as pavings, walls and lawn or green foliage.

Shift the location of the source is important for space planning design at micro level. The available natural source may have strong left or right, up or down delineation and may need the shift of illumination location. This is done by external and internal reflecting surfaces or use of light transmission tubes.

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DAYLIGHTING

Post 551  by Gautam Shah

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Daylight has Four important facets, the illuminance, warmth, colour and the variability. Each of these becomes a key issue for building design, how we conduct tasks and manage comfort. The chief source of daylight is the sun. It offers direct and indirect (‘diffused’) light. The earth’s daily rotation on inclined axis and elliptical rotation around the sun offers the variations, beyond the frequent changes in sun’s own output. Sunlight at Earth’s surface is around 52 to 55% infrared (above 700 nm), 42 to 43% visible (400 to 700 nm), and 3 to 5% ultraviolet (below 400 nm) spectrum. The quality of daylight at each place and moment is distinctive, creating unique time, space and environmental combination.

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Grand Station NY The natural flood of daylight is no longer available due to  high-rise buildings in the vicinity 

Daylight is the combination of all direct and indirect sunlight available outdoors during the daytime. Daylight as a natural light is considered mainly during the sunup to sundown period (and little more for the twilight periods). The amount of natural light available in any interior space is proportional to the daylight available outdoors. Daylight on an outdoor location is a combination of direct sunlight, diffuse sky radiation, and both of these as reflected from the earth and other objects. Light scattered in the atmosphere is referred to as diffused daylight. Sunlight scattered or reflected from other space objects, such as the moon is not considered daylight.

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Lighting without a window in the Pantheon Rome

Direct sunlight is that part of solar radiation which reaches the earth’s face without being scattered. It is a directed beam or a point source of light. Direct sunlight at noon can have illuminance as high as 120,000 lux (Compared to this moon light is <1 lux). Sunlight is a warm colour light, at noon, the colour-temperatures are about 5500°k, bluish-white or ‘cool colours’, and at sunset, these are about 2700-3000°k (degrees kelvin), are yellowish-white through red or called ‘warm colours’. This is similar to heated iron, like a horseshoe, it first glows red, but on further heating it turns to orange to yellow to white and, finally blue-white.

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Colours at sunrise due to temperature differences

Daylight consists of direct sunlight and it’s reflected or diffused component. Daylight arrives or disappears when the Sun is approximately 18° below the horizon. (As the Earth takes 24hoursx60=1440 minutes to complete its orbit of approximately 360°, the 18° translates into 72 minutes period on equator and 23°N to S. For different locations and seasons the twilight time could vary). This is a twilight zone of early or late day lighting, when the Sun itself is not visible, as it is below the horizon. Twilight occurs due to the scattering of sunlight in the upper atmosphere, which in turn illuminates the lower atmosphere. This is a period when shadows are not yet present, and objects are silhouetted against gradually brightening sky. In extreme regions like the arctic where Sun may not dip below 18°, the twilight may be seen between evening to morning night period.

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Three types of twilight within 18 degree –Wikipedia image by TWCarlson

The twilight effect is important for the stretched daylight period. It defines when street and other estate security lights can be switched on or off. It defines when certain outdoor activities like jogging, and exercises can be conducted. Interior areas of a building begin to receive illumination in the twilight period (near sunset or sunrise), allowing for switching on or off the artificial illumination.

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Golden gate bridge at Twilight Wikipedia image by Brocken Inaglory

A twilight zone has been accepted as a prayer time in many religions. Egyptians wished to experience the first rays of the sun, for these obelisks like tall structures were erected near the temple entrance. The tapered top face of an obelisk was covered with shiny metal to glitter in the first sun rays of the day. Similarly Buddhist and Hindu temples used columns topped with shining metal sculptures like Dharma Chakra or Toran of metal pieces. A twilight zone is the time when cattle go out or come back from grazing, raising dust in the sky. This Go-Dhuli period is considered the most auspicious time for Hindus.

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Twilight zone is cattle returning home after grazing with dust rising (GoDhuli time) -most auspicious period for Hindus India

Direct sunlight can warm up a surface depending on its angle and duration of exposure to the sun, surface colour and texture. Direct sunlight is the brightest illuminance and can be redirected through reflection to interior spaces by means, such as opaque reflectors, mirrors, tubes etc. It is used for generating electricity through solar panels. Direct sunlight casts a shadow, whereas diffused sunlight is scattered and arrives from all directions, so does not cast a distinct shadow. But, often enough diffused light arriving through highly directional openings, casts a dull shadow.

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Skylight in Star Ferry pier Hong Kong Wikipedia image by VictoriaDFong

Day-lighting is used for illuminating a dully lit space or object by use reflective surfaces, appropriate spatial orientation or exposure, time scheduling or through design and placement of openings. The primary intention is to save fossil and other sources of energy, better recognition, reduce the glare, adjust the contrast and for highlighting.

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Stratification of openings for Illumination and view II nd floor Children Library Bronx Library Center Wikipedia image by Julian A. Henderson

Daylight design takes into consideration the source and nature (intensity, colour) of the direct and diffused sunlight. One of the important holistic aspects of daylight design is the stratification of openings for illumination, and for view in and out. Stratification arises from the fact that daylight is arrives from the skies and grounds, both of which are strongly horizontal in effect. Daylight design is conditioned by the tasks to be handled, building form, siting, climate, architectural components and appendages, surface colours and textures in interiors, back up system of artificial illumination. At micro level design criteria include the opening size, shape, orientation, location, quality of glazing, opening treatments, position and orientation of interior components.

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DAY-LIGHTING – in Interior Spaces

Post 366 – by Gautam Shah

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Day-lighting or daytime natural illumination is an important requirement for Interior spaces. The illumination requirements vary for various tasks, background brightness (contrast or glare), forms of shadows, and movement or variations in levels of lighting. The direct sources of daytime natural illumination in interior space are openings like doors, windows, gaps, cracks, punctures, translucent or transparent walls, trellis, etc. Besides these there are number of indirect means that enhance or contrast the direct sources of illumination. These means are planer or curvilinear surfaces, reflective surfaces, colours and textures. The daytime illumination arrives to a built-form, from different directions and sources, such as directly from the source, from sky, and as the reflections from terrestrial objects. These sources include, direct sunlight, diffused sky radiation, and both of these as reflected from the terrestrial objects.

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The amount of daylight received into an interior space is defined as a daylight factor (being the ratio between the measured external and internal light levels). The external light level can be as high as 120,000 lux at noon for direct sunlight at noon, to less than 5 lux on very heavily cloudy evening.

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To gain maximum daylight into an interior space the building should have wider foot print and its perimeter should be linear or undulated. The building must be longer in North-South direction, compared to East-West direction, unless the space is meant exclusively for either Morning or Evening use. For Northern Hemisphere, North side and for Southern Hemisphere, the South side receives more daylight.

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The neighbourhood buildings and topography and immediate surroundings have a bearing on the quality of illumination entering a building. The reflected light from surfaces of buildings, colours of roads and pavements affect lower floors of the buildings. Reflections from sea front and movement of trees tops, due to the breeze, can have unsettling effect on interior spaces. Upper floors of tall buildings, except in similar localities, receive consistent, but very strong daylight from nominal windows. Such floors with bottom windows get disturbing reflections from traffic and other movements, reflected to the ceiling.

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Location of openings, their proportion to wall, and distribution, determine the distribution of day light in the interior space. In tropical climate zones and in colder climes during warmer months, open doors play a very important role in daylight gain. Similarly, open to sky Chowk or cutouts with surrounding passages or ‘livan’ like spaces allow distributed illumination.

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For good day lighting the interior spaces must have at least one face with exterior exposure, or with an abutting shading component like verandah or gallery. A skylight or upper level opening is an efficient source for natural illumination. A taller window leads the daylight deeper into the room space. The depth of daylight penetration is approximately two and one-half times the height of the opening.

High – performance glazing with downward inclination

The space planning of an interior layout must be optimized for daylight. Large tall pieces of furniture can act as mid space barricading element or as reflective surfaces. In commercial spaces half or fully glazed partitions can allow just sufficient illumination for passage areas. A plain ceiling at low level may not be as reflective as a stepped or contoured one.

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On exterior and interior sides use of light-shelves, against an opening, helps distribute the daylight and cut glare. A light shelf could be a small width blade of a louver to very large fixed or adjustable jalousie system. A high-performance glazing systems generally admit light without the heat gain.

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Reflectance of room surfaces impacts the perception of brightness in a space. The surface reflectance is a function of colour, its texture (matt, dull-sheen, glossy) and the orientation of grains of textures. Extreme levels of brightness are present in the same field of view, can be calibrated by surface design.

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Daylight must be planned and ‘attuned’ for requirements of tasks, posture, communication, expression and intra-personal relationships, Poor visibility, recognition, and discomfort result from lack of required levels of illumination, direction. To remove wearisome consistency (as with sky or high level openings), some variations in moment to moment daylight must occur.

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