[FDArchitects]

Design of the Lighting System

A simple means of designing lighting systems is achieved by means of the lumen method; this is a simplified design approach to enable the designer to achieve an even light distribution in spaces of reasonably simple geometry (i.e. rectangular).

The basis of the lumen method is the following equation:

          E X A
N= ------------------
     n x F x MF X UF


N - is the number of luminaires required;
E - is the required illuminance (lux);
A - is the area to be lit;
N - is the number of lamps per luminaire;
F - is the lamp lumen output (lumens);
MF - is known as the maintenance factor, which is a combination of three factors;
UF - is the utilisation and is a function of the luminaire properties and room geometry.


Utilisation Factor (UF)
The room geometry is a crucial factor in determining the utilisation factor term in the lumen equation. Several parameters are important.

In the Lumen method of design the room geometry is characterised by a room index (K):

        L X W
K = -----------
       (L+W)hm

L= length of room 
W= width of room 
hm = height of room ( distance between working plane and ceiling plane ) 


The calculation of surface reflectances is more complicated for imaginary planes such as the luminaire and working planes, in these cases the reflectances of these planes must be calculated as an equivalent cavity reflectance (ρe):



Utilization factors