3. First, you need to calculate
the coefficient of detection KR of the
environment, using the following
formula:
a = length of the room in meters;
b = width of the area in meters;
h = distance in meters between the
lighting fixtures and the plane on which
you have to measure illuminance (eg.
height of lighting fixtures 2.80 m,
worktop at height 0.8 m, h = 2.80 to 0.8
= 2).
4. Once you have obtained the value
of KR, you can determine the
minimum number of
measurement points “n” using
the following table:
5. a = length of the room
a1 = length of the measurement
zone
b = width of the room
b1 = width of the measurement
zone
n = the number of measurement
zones
a1 ≤ 2·b1;
a1/b1 ≤ 2;
zones with larger side ≤
2·zones with smaller side.
6. The average illuminance Em is given by the arithmetic mean of the
illuminance values measured at the center of zones:
Em = average illuminance
E1 ÷ En = illuminance values of the measured points
n = total number of measurement points
Analysis of the results
8. is the depreciation of light output over the time and it can be calculated via the
following equation:
MF or LLF= Lamp Lumen Depreciation (LLD) x Luminaire Dirt Depreciation
(LDD)
LLF is affected by many factors like; Temperature Dirt&Dust Over time
Light Loss Factor
9.
10. Method:
Horizontal Illuminance: The amount of light falling on the horizontal plane.
EXAMPLE: CONFERENCE ROOM
Calculation of Horizontal Illuminance & Point
11. TERMS:
I: Luminous Intensity, candela, cd
d: Distance, meters, m
E: Illuminance, Lux, lx
Ep: intensity of illumination
∅: Angle between incident ray and the normal line
Note: Normal line is a perpendicular to the surface considered.
14. Coefficient of Utilization (CU)/
Utilization Factor (UF)
• The ratio of the total flux received by the surface to the total lamp flux.
Factors influencing coefficient of utilization:
• The efficiency of the luminaire
• The luminaire distribution
• The geometry of the space
• The reflectance’s of the room surface
15. 1. Room Cavity Ratio (RCR)
hRC - Room Cavity Height
L - Length of the room
W - Width of the room
2. Ceiling Cavity Ratio (CCR)
hcc – Ceiling Cavity Ratio
3. Floor Cavity Ratio (FCR)
Hfc – Floor Cavity Ratio
Types of Cavity Ratio
17. Lumen Method/ Zonal Cavity Method
-Is a simplified method in
calculating the light level in
a certain room.
- Total number of lumens in a
room divided by the area of
the room.
18. FORMULA:
N = numbers of luminaires required F = initial luminous flux
output of each lamp (Lumens)
E = Planned Illuminance (lux) UF = Utilisation Factor
A= space area (L x W) (square meters) LLF = Light Loss Factor
Light Loss Factor: effects such as decrease in light output caused by the fall in
luminous flux with hours of use the deposition of dirt on luminaire it is also
called the maintenance factor.
Lumen Method
19. Problem Example:
You have been employed as a lighting
engineer for the University of Unity. A
lecture theater measuring 30m x 10m
requires a service Illuminance of 750 lx.
The type of lights to be used is strip
fluorescent lamps in a recessed louver
with reflecting surfaces with a luminous
flux output 4,050 lm and reflectance’s of
0.7 ceiling and 0.1 walls. Calculate the
room index and calculate the lamps
number.
Given:
LLF = 0.95 UF = 0.42
Room height = 4.5m
Working height = 1m
Solution:
L = length of room (m)
W = width of room (m)
Hm = Height of luminaire above working surface
1. N = __ (30) (10) __
2.N = __750 x (30 x 10) __
3.5 (30 + 10)
4,050 x 0.42 x 0.95
= _300_
= 139.24 lamps
140
= 2.14
20. Point Method
• This method is applicable where the
illumination at a point due to one or more
sources of light is required.
Three Factors
1. Luminous intensity
2. Distance
3. Orientation of the surface
Candlepower
Distribution Curve
1. Rotational
symmetrical
2. Planar symmetrical
3. Asymmetrical
Inverse
Square Law
21. Luminous Intensity Inverse Square Law
Orientation of the Surface Formula: E = I/ d2 cos θ
Formula: E = I/ d2
22. Point to point or Inverse
Square Law method
• Inverse Square Law states that
Formula: E = I/d2
SI unit = lux
Where:
E = Illuminance on the surface
(lux, lx)
I = Luminous intensity of the
source in the direction of the
surface (candela, cd)
d = Distance from the source to the
surface (meters, m)
Problem # 1:
Solution:
Formula: E = I/d2
Given:
I = 179cd
d = 2m
E = 170/22
E = 42.5 lx
23. Problem # 2:
Where:
θ is the angle between the light ray
coming from the source to the point, and
a line that is perpendicular (normal) to the
plane or surface on which the illuminance
is being measured or calculated
This example will consider the
illuminance at a single point on a
horizontal surface from a single
luminaire straight down
Given:
D = 2.13 m
θ = 15°
LLF = 0.85
I = 2200 candelas
Solution:
E = I/ d2 x cos θ x LLFTOTAL
E = 2200 cd x cos 15° x 0.85 / 2.13 m2
E = 398 lux (maintained)
Formula: E = I/ d2 cos θ
27. 2. Effects such as decrease in light output caused by the fall in
luminous flux with hours of use the deposition of dirt on luminaire it
is also called the maintenance factor.
28. 2. The amount of light falling on the horizontal plane.
Light Loss Factor
29. 3. What are the factors influencing coefficient of utilization?
30. 3. What are the factors influencing coefficient of utilization? Give at
least 2.
• the efficiency of the luminaire
• the luminaire distribution
• the geometry of the space
• the reflectance’s of the room surface
