Post 593 –by Gautam Shah
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.
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.
■ 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.
■ 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.
■ 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.
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.
● 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.
● 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.
● 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.
● 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.
● 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.
● 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.
● 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.