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Lighting architecture lecture 2
1. CALCULATING DAYLIGHT FACTOR
âąDaylight â admitted into bldg. through windows / roof-lights.
âąAmount of light received inside a bldg. will constantly vary.
âąImpracticable to express interior daylighting in terms of
illumination actually obtainable inside a bldg. at any time.
âąFor practical purposes â Daylight Factor (DF) is used.
2. CALCULATING DAYLIGHT FACTOR (DF)
DF â percentage ratio of the instantaneous illumination level at a
reference point inside a room to that occurring simultaneously outside
in an unobstructed position.
ï Daylight factor is measured as the ratio of illumination at the working
plane inside a room to the total light available outside. This is called
daylight factor which is expressed in %.
ïDF â ratio of internal light level to external light level.
ïDF = (Ei / Eo) X 100%
Where, Ei â illuminance due to daylight at a point on the indoors
working plane.
Eo â simultaneous outdoor illuminance on a horizontal plane from an
unobstructed hemisphere of sky.
3. DAYLIGHT FACTOR
ïDF includes the following :
(a) Sky component (SC): direct light from a patch of sky visible at
the point considered.
(b) External Reflected Component (ERC): light reflected from an
exterior surface and then reaching the point considered.
(c) Internal Reflected Component (IRC): light entering through the
window but reaching the point only after reflection from an internal
surface.
ïSum of the 3 components gives the illuminance level (LUX) at the
point considered.
Lux = SC + ERC + IRC
ïD.F. used in bldg. design in order to assess the natural lighting level as
received on the working plane.
4. CALCULATING DAYLIGHT FACTOR
ï±A simple RULE OF THUMB can be used to approximate D.F.
D = 0.1 X P
where D = Daylight factor
P = Percentage glazing to floor area
E.g., given a room of 100 sq.m. floor area with 20 sq.m. of glazing.
D = 0.1 X (20/100)X100
= 0.1 X 20
= 2 %
ï±Calculation of natural illuminance at the reference point inside a bldg.
by applying the following formula,
D = (Ei / Eo) X 100
Where, D = D.F.
Ei = illuminance at reference point in bldg.
Eo = illuminance at the reference point if the room was unobstructed.
5. THE DESIGN SKY CONCEPT
When the Daylight Factor for a given point has been established, it can
be converted into an illumination value, if the outdoor illumination is
known.
E.g.1:
Both factors of E are measured in lux (lumens per sq.m.) with Eo taken
as standard 5000 lux for unobstructed sky in the UK, DF = 2%.
Therefore, D = (Ei / Eo) X 100
or Ei = (D X Eo) / 100
= (2 X 5000)/100
= 100
Therefore, Ei = 100 lux.
6. THE DESIGN SKY CONCEPT
E.g.2: If DF = 8%, & Eo = 6000 lux
DF = (Ei / Eo) X 100
8 = (Ei / 6000) X 100
Ei = (8 X 6000)/ 100 = 480 lux
âąBy statistical evaluation of long term illumination records an out-door
illumination level (Eo) can be established for a given location - this is
taken as the âdesign skyâ illumination value for the particular location.
âąSome typical âdesign skyâ illumination values (in lux) are:
Location Latitude Illumination (lux)
London Lat. 52â° 5 000
Sydney Lat. 33â° 8 000
Brisbane Lat. 27â° 10 000
Darwin Lat. 10â° 15 000
Nairobi Lat. 1â° 18 000
Delhi Lat. 29â° 6 000
7. THE DESIGN SKY CONCEPT
Previous calculation can be reversed & used as a basis of design:
ïEstablish required illumination level â e.g., 300 lux.
ïAscertain local âdesign skyâ illumination, Eo â e.g., 9000 lux.
ïCalculate necessary daylight factor:
DF = (300/9000) X 100 = 3.33%
ïManipulate the design variables (window size etc.)to achieve this
daylight factor.
8. DAYLIGHTING:
ï§ Practice of placing windows or other openings & reflective surfaces so
that during the day natural light provides effective internal lighting.
ï§ Objective â to maximize visual comfort to reduce energy use.
ï energy saving achieved by reduced use of artificial lighting.
ï or from passive solar heating & cooling.
ï§ Use of artificial lighting energy can be reduced by
ïInstalling less number artificial lights
ïDimming / switching artificial lights automatically in response to
the presence of daylight (Daylight Harvesting).
ï§ Daylight harvesting: term used in sustainable architecture for a
control system that reduces the use of artificial lighting in bldg. interiors
when natural daylight is available, in order to reduce energy
consumption.
9. LIGHTING IN THE TROPICS
Tasks & problems of daylighting in tropical climates:
âąTo provide adequate daylight even if the windows are protected by
louvres for thermal reasons.
âą To exclude from visual field excessively bright (light coloured,
sunlit, etc.) surfaces which would cause glare.
HOT-DRY CLIMATES:
ïDirect sunlight must be excluded from bldgs. â reasons:
âąThermal
âąCreate glare
ïWindows tend to be small â not much sky will be visible from any
point indoors â hence SC (sky component) is insufficient.
ïGround & external surfaces of other bldgs. are usually light coloured â
in strong sunlight these may create glare â hence ERC can be used with
provision to avoid glare.
10. indoor
External
surface
Ground surface
outdoor
Sun
ïInternally reflected light
â most convenient form of
daylighting.
ïSuitable arrangement â
high level window â sill
above eyelevel â would
admit reflected light to the
ceiling.
ïIf the ceiling is white â
above method would
ensure sufficient & well
diffused interior light
through a small window.
indoor
outdoor
11. ï sunlit reflective surfaces of shading devices â can cause glare â hence
should be non-reflective.
ïLow level windows â acceptable if they open onto a shaded / planted
courtyard.
WARM HUMID CLIMATES: Buildings have
âąLarge openings to ensure cross ventilation & air movement.
âąProvided with wide overhanging eaves or shading devices.
ï Direct sunlight is excluded â thermal reason - bright sky could
provide sufficient light - but its high luminance would cause glare -
view of sky should be screened by shading device / plants.
ï Sky luminance - less near the horizon than at higher altitude angles
- view of sky up to about 15â° may be permissible.
12. 15â°
indoor
outdoor
Criteria for the design of
shading devices:
âąPermit view of sky near
the horizon only.
âąExclude view of bright ground & sunlit blade / louvre surfaces.
âąDaylight should be reflected from ground & louvres to the ceiling â
ceiling should be of light colour.
13. SUPPLEMENTARY ARTIFICIAL LIGHTING:
âąIn moderate climate (prevalent temperatures are neither too hot nor
too cold) â difficult to provide adequate daylight in side-lit rooms - to a
depth greater than three times the window head height (6m approx.)
âąFor rooms deeper than this â a system known as PSALI (permanent
supplementary artificial lighting of the interiors) has been developed -
interior parts of the room are lit permanently by electric lights to
provide necessary illumination.
âąPAL system â Permanent artificial lighting â ignores daylight
altogether â windowless environment â window is the weakest point of
the building â in both thermal & noise insulation â saving on heating &
air-conditioning > cost of artificial lighting.
âąCounter argument â purpose of window â not only to provide daylight
â but also to provide a visual link with outside world
âąPSALI system â would satisfy the need with reduced windows -
insufficient daylight would be supplemented by artificial light.
âąIn hot-dry regions windows are small for thermal reasons â daylight
reaching interiors is insufficient.
14. DAYLIGHTING
âąWe turn toward the sun, seeking light and warmth - to nourish both
spirit and body.
âąPosition of the sun in the sky / colour of its light - keep us in touch with
the time of day / season of the year.
âąIntensity of sunlight is so great that no artificial light can match it.
âąWhile building houses - important to locate and organize them in a way
that allows all important spaces to receive abundant natural light.
âąPlacing the house on the site to take best advantage of available light
requires a study of the light and shadow patterns created by
surrounding structures, by the topography, and by landscape elements.
15. DAYLIGHT
âąA primary goal is to bring light into each room from two sides.
A Simple four-square
house allows light
into two sides of
each corner room.
A house with wings
creates rooms with the
potential for light on
two or three sides.
A long thin house
allows light to
enter from
opposite sides of
most rooms.
16. DAYLIGHTING
Daylighting is the complete process of designing buildings to utilize
natural light to its fullest. It includes the following activities:
âąSiting the building â orienting for optimum solar orientation.
âąMassing the building â presenting the optimum building surfaces
towards the sun.
âąChoosing fenestration to permit the proper amount of light into the
building, taking into account seasons, weather, daily solar cycles.
âąShading the façade & fenestration from unwanted solar radiation.
âąAdding appropriate operable shading devices, e.g., blinds, curtains, to
permit occupant control over daylight admission.
âąDesigning electric lighting controls â energy saving benefits of
daylighting.
17. DAYLIGHTING â TOPLIGHTING CONCEPT
SKYLIGHT TOPLIGHTING
âąUse of skylights to introduce light from above.
âąBest done with diffusing skylight to prevent
direct sun rays from causing overly bright spots.
âąSkylights should be no more than 5% - 6% of
the roof area.
CLERESTORY TOPLIGHT
âąUse of high windows, above ceiling line.
âąBest done when the windows faces north
to prevent direct solar radiation.
âąWith north facing fenestration, ceiling
aperture can be very large.
18. DAYLIGHTING â TOPLIGHTING CONCEPT
SAWTOOTH CLERESTORY TOPLIGHTING
âąAngled ceiling produces more indirect light â
increasing the efficiency of skylight.
âąBest if north facing.
DOUBLE CLERESTORY TOPLIGHT
âąBest if long axis is oriented east & west
âąUse passive shading on south side to
prevent direct solar radiation into the
space.
19. DAYLIGHTING â SIDELIGHTING
âąSide lighting employs vertical fenestration (usually windows) to introduce natural
light.
âąUnlike top lighting, side lighting tends to introduce light that can be too bright â
causing glare.
âąDesirable view provided by windows makes glare an acceptable side effect.
âąSidelighting on east, south & west can permit direct solar glare & heat gain -
necessary to shade windows to prevent excessive glare & gain.
âąOverhang soffits provide a limited
amount of shading.
âąBest employed on the south façade
(northern hemisphere) of the building.
indoor
sun
SOFFIT OVERHANG
20. DAYLIGHTING â SIDELIGHTING
âąAwnings / other extended shades
offer additional protection.
âąGenerally needed on the east &
west façade of the building.
âąA light shelf provides both shading &
indirect lighting for the space â
increasing the amount of daylight
depth penetration.
âąMost effective on the south façade â
can be employed on east /west façade.
indoor
sun
indoor
sun
AWNING
LIGHT SHELF
21. BASIC PRINCIPLES OF DAYLIGHTING DESIGN
1. Plan the building such that every regularly occupied living space has
access to a window/skylight - high priority to windows that provide
a view â effective day lighted area extends about 2 times the width
of a window & about 2 - 2.5 times its height.
2. Minimize the size of east/west sides of the building, maximize the
south/north sides. North facing windows present no solar heating
problems, south facing windows can be protected with
overhangs/awnings/light shelves.
3. If a large area of the building is not near a window â provide toplight
skylights in single story buildings / top floor of multistory buildings
â skylights should occupy 3% - 5% of roof area.
4. Protect the interior from too much natural light â employing
appropriate window glass, external shading devices, internal shading
devices etc.
5. Provide an electric lighting system and or automatic lighting controls
to permit daylight harvesting. The best way is to dim the electric
lights rather than switch them on & off.
22. SUNâS PATH
âąThis house plan is one that takes full advantage of
the light and the spectacular views.
âąBasic form of the house - a two-story rectangle
with chamfered corners facing south.
SITE PLAN
FIRST FLOORGROUND FLOOR
âąBy setting the
house with its
leading corner
facing south, two
full sides of the
building receive
south sun, filling
the interior with
light from
morning until
night.
23. âąA wide verandah with a balcony above wraps the south corner.
âąWhen the sun is lower in the sky - early morning and evening & winter
âthe low angle sun allows light to penetrate the verandah and enter the
rooms beyond.
âąThree bedrooms have windows to the east; as the sun rises it gradually
fills the rooms with light. Each bedroom also has windows on a second
wall, balancing the light in the room and increasing the period of direct
sunlight. By mid-afternoon, the bedrooms are protected from heat gain
by the placement of the bathroom and fireplace to the west.
FIRST FLOORGROUND FLOOR
âąAt breakfast, the eastern
sunlight enters the kitchen
& adjoining dining room.
âąVerandah shades the
south side on the lower
floor, giving midday
protection to kitchen &
living room.
24. âąBy late afternoon, the sun moves to the west and enters through the
corner windows of the living room - it is important for afternoon /
evening activities to have a sense of the light but also to be protected
from heat gain - protection is created by dense landscaping outside the
corner windows, which blocks the sun as it gets low in western sky.
âąPlacing the house diagonally to the south takes maximum advantage of
available sunlight. Every room gets direct sun at some point during the
day.
FIRST FLOOR
GROUND FLOOR