Utilization factor or co-efficient of utilization it may be define as “ the ratio of total lumens received on the working plane to the total lumen emitted by the light source.

Utilization factor= lumen received on the working plane/ lumen emitted by the lamp.

Factor effecting utilization factor.

a) Type of light

b) Light fitting

c) Color surface of wall and ceiling

d) Area of illuminated

e) Mounting height of lamp

Its value lies between 0.4 and 0.6 for direct fitting.

It varies from 0.1 to 0.35 for indirect fitting.