Lighting and Acoustics
Arch 353
Dr. Abdelrahman Elbakheit
References
1. ‫ أستاذ الدكتور محمد عبد الفتاح عبيد‬, ‫اسس االنارة المعمارية‬
2. Architectural Lighting, M. David Egan and Victor Olgyay.
Photometry:
‫الفوتومترى‬
The science of light measurements and characteristics
Shadow and Semi-Shadow:
‫الظل و الظليل‬
When a point source light is obstructed by an opaque object it forms a shadow.
If the light source is large in size compared to the obstacle, a dark area with less
light is formed around the shadow called Semi-shadow.
Luminous flux: ‫الفيض الضؤى‬
It is the flood of light out of a light source as an electro magnetic waves.
This flood regardless of it’s direction is measured in LUMEN/s.
Our eyes senses this flood and sees the surroundings.
our ability to see is not dependent on this flood of light only, but also on the wave
length of it’s electro-magnetic components.
Maximum wave length perceived by our eyes is for the yellow-green colour (5550
Angstrom)
Lumen (lm):
- If we have a candle radiates light in all directions, situated in the focal point of a sphere with a unit
radius. Then the light falling on a foot square of the sphere’s surface is called the lumen.
- The sphere surface area is ( 4 π R2), then the overall light on the sphere surface would be 12.57
Lumens.
Inverse square Law:
-Light intensity changes with the change of distance between the light source and the recipient
surface, so that light quantity on a surface is inversely proportional to the square of the
distance from the light source.
Therefore light L = Light from the source/(distance)2.
- If the recipient surface is inclined by an angle (θ) then the light received would reduced by cosθ
than that normal to the direction of light.
Illumination (Luminance) ‫ االنارة‬:
-Illumination is the light intensity on unit area at the plane of illuminated surface.
-
In SI units : illumination is light flux of one Lumen on a unit metre square. This quantity of
illumination is know as the LUX.
-
Imperial units know as Foot Candle (FC), which is light flux of one Lumen on one foot
square.
One FC = 10.76 Lux.
-
Initial illumination: ‫االنارة االبتدائية‬
It is the amount illumination on a unit area when the light fixture is new.
Efficacy of Lamps and Luminaries: ‫مفعولية المصابيح و وحدات االنارة‬
-
For lamps It is a ratio between the output of lamps in Lumen to the input in Watts
η = Lumens output / Power input in Watts = lumen / Watt………………………………………... 1
-
Efficacy for luminaries is the ration between the lumens input to the lumens output…..2
-
Total efficacy for luminaries with lamps = 1 x 2= lumens output from luminaries / Watts input.
Luminance (Brightness): ‫السطوع‬
We distinguish between shapes and colours according to its brightness, i.e., according to the
light emitted or reflected from a unit area.
For instance if we have some ink on white paper. If we subject 100 candles on it. The paper has
85% reflectance and the ink has 10%. Then we get about 85 candles from the paper and 10
candles from the ink. Thus making it easy to read.
Units of Luminance:
are a reflection to illumination to each unit area.
Units of Luminance:
Are reflections to illumination to each unit area.
In empirical system : Foot Lambert, which is the number of Lumens from a square foot.
In SI system : Nit, the Brightness of one metre square emitting one candle.
1 Nit = 1 candle/m2.
Sources of Luminance (brightness):
-
Luminance form light emitting objects, the sun, lamps. Etc…
Luminance from penetrating objects, the Clouds, Luminaries. Etc…
Luminance from light reflecting objects, the Moon, furniture. Etc…
Luminance for light emitting or penetrating = (Candle power x Efficacy) / (radius of lighting
source)2