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Light Calculations PDF

The document discusses lighting calculations and factors that affect illuminance calculations. It defines key terms like illuminance, luminance, luminous efficacy, utilization factor, room maintenance factor, and light loss factor. It also provides an example calculation of point illuminance level from an overhead light bulb and describes the lumen method for calculating average illuminance on a horizontal working plane using factors like lumens per lamp, utilization factor, and light loss factor.

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talal ilyas
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187 views26 pages

Light Calculations PDF

The document discusses lighting calculations and factors that affect illuminance calculations. It defines key terms like illuminance, luminance, luminous efficacy, utilization factor, room maintenance factor, and light loss factor. It also provides an example calculation of point illuminance level from an overhead light bulb and describes the lumen method for calculating average illuminance on a horizontal working plane using factors like lumens per lamp, utilization factor, and light loss factor.

Uploaded by

talal ilyas
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Lighting calculations

The Illuminance: (E)


Luminous Flux / area of the sphere
surface
E=Φ/A
E= I/ r2
= lumen/ m2 = lux
The luminance (Luminous Intensity) (I)
I= Φ/ω cd
Where: ω = solid angle

= (Φ/A)* r2
= E* r2 Candela
Inverse square law: Double the Radius:
• Surface area bounded by a solid angle of 1 sr now increases to 4m2
• Luminous flux remains Φ = 1lm
• Illuminance E drops from 1 lux to ¼ lux
What can we do with this?
It’s the basic building lighting
We can find the illuminance on a desk from a incandescent light
bulb overhead:

Bulb: 60W * 20 lm/W = 1200 lm


1200/4π 100 cd if point source
Desk : E = 100/22 = 25 lux

LUMINOUS EFFICACY
Is the ratio of the luminous flux emitted by a lamp to the power taken
by it. (unit: LUMENS PER WATT, lm/W)
Calculation of point illuminance level:
Ep
Which are generated by individual light source:

}E = I/r2
But, r = h/ cos ( )
So,

E p = I /h2 cos3

} Where,
} Luminous Intensity(I)
} Hieght (h)
} Light Incidence Angle ( )
Factors affected on illuminance calculations

1. Room Reflectance
} The room is considered to
consist of three main
surfaces:
(a) the ceiling cavity,
(b) the walls, and
(c) the floor cavity (or the
horizontal working plane).

} The effective reflectances of the


above three surfaces affect the
quantity of reflected light received by
the working plane.
Factors affected on illuminance calcuations
2. Luminaire maintenance 3. Room surface
factor (LMF) is the proportion maintenance factor (RSMF)
is the proportion of the
of the initial light output from a illuminance provided by a lighting
luminaire after a set time to the installation in a room after a set
initial light output from a lamp after time compared with that occurred
a set time. when the room was clean.
} Three factors must be considered in
its determination:
4. Utilization factor (UF) is
(a) the type of luminaire, the proportion of the luminous
(b) atmospheric conditions, and flux emitted by the lamps which
reaches the working plane.
(c) maintenance interval. Factors that affect the value of UF
are as follows:
(a) light output ratio of luminaire
(b) flux distribution of luminaire
(c) room proportions
(d) room reflectance
(e) spacing/mounting height ratio
Lumen Method Calculations
Where:
E = average illuminance over the horizontal working plane
n = number of lamps in each luminaire
N = number of luminaire
F = lighting design lumens per lamp,
i.e. initial bare lamp luminous flux
UF = utilisation factor for the horizontal working plane
LLF = light loss factor
A = area of the horizontal working plane
The Luminous Flux (Φ)= EA/MU
Ø Calculate the utilization factor
Ø Calculate the Room Factor:
K = 0.8W + 0.2L
he
Where: W= width of the room
L = length of the room

Ø From the table find “η”


Ø The Luminous Flux (Φ)=
EA
η
Room Factor
is the proportion of the initial light output
from a luminaire after a set time to the
initial light output from a lamp after a set
time.

} It depends on room dimension

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