M.Sc.(Eng) in Building Services Engineering

UNIVERSITY OF HONG KONG

FACULTY OF ENGINEERING

M.Sc.(Eng) in Building Services Engineering

MEBS6002 2010 LIGHTING ENGINEERING

Tutorial

1). A room measures 4m(W) x 5m(D) x 2.7m(H). There is a window, 1.2m(H) x 1.8m(W), on the 4m(W) wall. Window sill is 0.9m above floor level.

a). Calculate the average daylight factor on the working plane, in percent, for this room, assuming that the window is not obstructed, transmittance of glass is 0.72, weighted average reflectance of all room surfaces is 0.5.

Give your answer to one digit after the decimal point.

b). Does the window height satisfy the limiting depth recommendation?

Assume that RBACK is also 0.5.

2). An office measures 10m(W) x 8m(D) x 3m(H). A window of 6m(W) x 2m(H) is located at centre of the 10m(W) wall. Window head is 2m above floor level.

Reflectances of the ceiling/ wall/ floor are 0.7/ 0.5/ 0.3 respectively. This window is made of 6mm thick clear float glass, with metal frame. The office is located in urban area but the area is clean, and the room surfaces are cleaned once a year. The window is not sheltered from rain nor exposed to heavy rain.

Calculate the daylight factor at floor level at a rear corner away from the window.

The view is obstructed by a building of 5° angular height continuously, and it can be assumed that this obstruction subtends 5° anywhere in the room. Reflectance of the obstructing building is 0.1.

3) / a. / Derive an expression for the total average illuminance, , on the inside surface of an integrating sphere in terms of A (interior surface area), FL, (flux generated by the light source inside) and ρ (reflectance of the interior surface)

b. / Explain how the flux output of a lamp can be measured by means of an integrating sphere. State any precaution required.
4) / a. / Let F1,2 be the flux transfer from surface 1 to surface 2, while F2,1 is the flux transfer from surface 2 to surface 1. And let M1 and M2 be the luminous exitance of surface 1 and 2 respectively.
Prove that if these 2 surfaces are perfectly diffusing, then

b. / Similarly, prove that the same relationship holds for non-perfectly diffusing surfaces provided they are parallel to each other.
5) / IESNA points out that there are 9 methods of optical control. What are they?
6) / a. / Briefly describe the different forms of light pollution.
b. / Suggest lighting techniques that can be used to reduce light pollution.
7) / For a floodlighting installation, prove that

and,

where
while
and
The subscripts L, A, and P refer to the lamp, the aiming point and the point to be illuminated.
8) / An array of floodlights are positioned together at coordinates (-10m, 35m, 30m) and aimed at (60m, 15m, 0m). The array consists of 25 floodlights. Each floodlight has a 1000W metal halide lamp and the intensity distribution of the luminaire is proportional to cos4θ where θ is the angle to the aiming vector, and each has peak intensity at aiming angle of 90,000 candelas. If a camera is located at C = (110m, 60m, 5m), or 5m above ground, calculate the luminance of a surface normal to the camera viewing direction at point P = (100m, 0m, 2m). Assume that the surface is a perfect diffuser with reflectance of 0.5.
[Ans: 3.6cd/m2]
9) / a. / A floodlight is positioned at the coordinate (-10, -15, 20) and it is aimed at (25, 10, 0). Find the horizontal and vertical angles at a point P = (35, 20, 1). All units in metres.
(Ans: -6.5o, 2.2o)
b. / If a camera is located at (30, 15, 2), and the intensity of the floodlight at the horizontal and vertical angles calculated in (i) above is 150,000 cd, calculate the illuminance at point P on a plane normal to the direction of the camera. (Ans: 40.6 lux)
10) / a. / An array of floodlights is positioned at the coordinate (-10, -5, 10) and it is aimed at (35, 10, 0). Find the horizontal and vertical angles at a point P = (10, 25, 1). All units in metres.
(Ans: vertical angle 5.6o, horizontal angle 36.6o, intensity 440 cd/klm)

b. / Photometric data of the floodlight can be seen in the above diagram. Now the array consists of 25 sets of this type of floodlights and each floodlight is equipped with a 400W SON deluxe lamp. Calculate the horizontal illuminance on point P. Data of the lamp can be seen in the following table.
(Ans: intensity 418,000cd, distance between lamp and point is 37.2m, angle of incidence 76o, 73.3 lux)

c. / If a camera is located at (0, 10, 2), calculate the illuminance at point P on a plane normal to the direction of the camera.
(Ans: angle between camera vector and illumination vector 10.8o, 297.3 lux)
d. / Hence, calculate the luminance of a matt surface at point P on a plane normal to the direction of the camera. Given reflectance of the surface is 0.5.
(Ans: 47.3 cd/m2).
11) / a. / A number of engineers always say that “one must refer to manufacturers’ data for utilization factors of a lighting installation because UF’s of luminaires differ from one make to another”. Comment on this statement.
b. / Maintained illuminance calculated by the lumen method assumes an empty room. What will happen to the measured illuminance of a new lighting installation when furniture is moved in?
12) / Prove that the zone factor between angles of elevation and is

13) / From the polar curve of a luminaire, the following intensities, cd/klm, can be read in different zones:

Mid zone angle, measured from the downward vertical, degree

/ 5 / 15 / 25 / 35 / 45 / 55 / 65 / 75 / 85
Intensity, cd/klm / 128.7 / 128.4 / 125.9 / 123 / 118 / 110.6 / 102.2 / 92.7 / 79.1
Mid zone angle, measured from the downward vertical, degree / 95 / 105 / 115 / 125 / 135 / 145 / 155 / 165 / 175
Intensity, cd/klm / 72.4 / 73.2 / 61.7 / 44.9 / 27.9 / 13.3 / 2.7 / 0.94 / 0.94
If this type of luminaire is installed in a room having a room index of 1, and at a nominal spacing to mounting height ratio of 1.75, calculate the utilization factor of this installation?
Given that the reflectances of the ceiling cavity, walls and floor cavity are 0.5/0.3/0.2 respectively, and all these room surfaces can be considered as perfectly diffusing reflectors. Also assume that the room is square.
Use zonal multipliers for discrete light sources from the table contained CIBSE TM5.
(Answer = 0.375)
(Hint – this question is extracted from Example 2 of CIBSE TM5)
14) / The lighting installation in a room has a light output ratio of 0.8, while the downward light output ratio is also 0.8, direct flux on floor cavity is 0.55.
The room is 16m wide x 16m long. The mounting height is 2m. Reflectance of ceiling cavity / walls / floor cavity is 0.7, 0.5 and 0.2 respectively. Calculate the utilization factor of this lighting installation.
(Ans: 0.722)
15) / a. / A manufacturer publishes the following intensity distribution for a luminaire:
Angles of elevation, degrees, / Intensity, cd/klm
0 to 10 / 161
10 to 20 / 172
20 to 30 / 180
30 to 40 / 169
40 to 50 / 141
50 to 60 / 91
60 to 70 / 69
70 to 80 / 46
80 to 90 / 14
90 to 100 / 15
100 to 110 / 50
110 to 120 / 101
120 to 130 / 96
130 to 140 / 56
140 to 150 / 19
150 to 160 / 4
160 to 170 / 1
170 to 180 / 1
SHmR = 2
Calculate the LOR, DLOR and ULOR of this luminaire.
(Ans: LOR = 0.89, DLOR = 0.58, ULOR = 0.31)
b. / Calculate proportion of flux reaching the working plane directly if the above type of luminaires is installed in a room having room index of 2.5.
(Ans: 0.44)
c. / The above luminaires are installed in a 10m x 10m x 2.8m(H) room. Reflectances of the ceiling, wall and floor cavity are 0.7, 0.5, 0.2 respectively. Calculate the utilization factor of this lighting installation on a working plane 0.8m above floor.
(Ans: 0.74)
16) / a. / A manufacturer publishes the following intensity distribution for a luminaire:
Angles of elevation, degrees, / Intensity, cd/klm
0 to 10 / 132
10 to 20 / 147
20 to 30 / 160
30 to 40 / 155
40 to 50 / 132
50 to 60 / 105
60 to 70 / 89
70 to 80 / 94
80 to 90 / 0
90 to 100 / 0
100 to 110 / 0
110 to 120 / 0
120 to 130 / 0
130 to 140 / 0
140 to 150 / 0
150 to 160 / 0
160 to 170 / 0
170 to 180 / 0
SHmR = 1.5
Calculate the LOR, DLOR and ULOR of this luminaire.
(Ans: LOR = DLOR = 0.61, ULOR = 0)
b. / Calculate proportion of flux reaching the working plane directly if the above type of luminaires is installed in a room having room index of 3.
The zonal multipliers for discrete light source at SHmR = 1.5 and room index of 3 are given below:
Angles of elevation, degrees / Zonal multiplier
5 / 1.000
15 / 1.000
25 / 1.000
35 / 0.966
45 / 0.774
55 / 0.695
65 / 0.599
75 / 0.315
85 / 0.005
(Ans: 0.45)
c. / The above luminaires are installed in a 12m x 12m x 2.8m(H) room. Reflectance of the ceiling, wall and floor are all 0. Calculate the utilization factor of this lighting installation on a working plane 0.8m above floor.
(Ans: 0.45)
17) / 200W GLS lamps are used to illuminate a 12m x 8m room. If the maintained illuminance required is 200 lux, utilization factor of the installation is 0.5, maintenance factor is 0.8, lamp efficacy is 10lm/W, calculate the minimum number of fittings required.
18) / a. / For a luminous ceiling illuminating the floor, prove that the zonal fraction transfer from ceiling to the floor between angles of elevation of 1 and2 is
ZFR = (cosn+11 - cosn+12)
if the intensity distribution of the luminous ceiling is Iθ = I0cosn
where I0= is the maximum intensity emitted by the ceiling in the downward vertical direction.
b. / Hence prove that the zonal fraction transfer from the luminous ceiling to the floor is
ZFR = (cos21 - cos22)
if the luminous ceiling is a cosine diffuser.
19) / The utilization factor of a lighting installation can be calculated by
UFf = TF(C,F)DFc + TF(F,F)DFf + TF(W,F)DFw
where
UFf / = / utilization factor
DFc / = / ratio of direct flux on ceiling from the luminaire installation
DFf / = / ratio of direct flux on floor from the luminaire installation
DFw / = / ratio of direct flux on wall from the luminaire installation
TF(C,F) / = / transfer factor, ceiling to floor
TF(F,F) / = / transfer factor, floor to floor
TF(W,F) / = / transfer factor, walls to floor
Prove that



where
ρc / = / reflectance of ceiling (or ceiling cavity, as the case may be)
ρf / = / reflectance of floor (or floor cavity, or reference plane as the case may be)
ρw / = / reflectance of walls
fcf / = / transfer function (form factor), ceiling to floor
RI / = / room index
State any assumptions you make.

K.F. Chan (Mr.) Page 1 of 10 Mar., 2010

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