(a) Calculate the room
index.

(b) Determine the effective reflectances of
the ceiling cavity, walls and floor cavity.

(c) Determine the utilisation factor from
the manufacturer's data sheet, using the room index and effective surface reflectances as
found in (a) and (b) above.

(d) Determine the light loss factor.

(e) Inert the appropriate variables into
the lumen method formula to obtain the number of luminaires required.

(f) Determine a suitable layout.

(g) Check that the geometric mean spacing
to height ratio of the layout is within the SHR NOM range:

(h) Check that the proposed layout does not
exceed the maximum spacing to height ratios (SHR MAX).

(i) Calculate the illuminance that will be
achieved by the final layout and check against the standard.

Design a lighting installation for a
college seminar room so that the average illuminance is 500 lux on the horizontal working
plane, using the data listed below. Suggest the layout and check appropriate spacing to
mounting height.

Room dimensions:
12 m long x 8 m wide x 3.2 m high

Working plane at
0.7 m above floor

Reflection
factors: Ceiling 70 %

Walls 50 %

Working plane 20
%

Light Loss
factor: 0.779

Luminaires: 1800
mm twin tube with opal diffuser

Ceiling mounted

Downward light
output ratio 36 %

SHR MAX 1.60 : 1

SHR NOM 1.50 : 1

Dimensions :
1800 mm long x 200 mm wide

Lamps: 1800 mm
75 W plus white

5800 average
initial lumens per lamp

(a) __Initial calculation__

__
__
From manufacturer's photometric data sheet
(Table 3), utilisation factor (UF) is 0.5336 by interpolation.

Therefore, the number of luminairs is 10.

Initial check on S/Hm ratio gives:

From the manufacture's photometric data,
maximum S/Hm is 1.6 : 1. Therefore, it should be possible to use 10 luminaires.

(b) Proposed layout

A 5 x 2 array is proposed fro the lighting installation. (A
10 x 1 array is an alternative.)

(c) Checking the proposed layout

Since 2 x 1.8 m = 3.6 m < 8 m (width of room), the
proposed layout will fit.

(Usually checking only the linear
dimension of the fitting for space is enough as the other dimension (i.e. 200 mm in this
case) is much smaller.)

**
**For long axis,

For short axis,