Discussion about Maintenance factor Absorption factor,Reflection factor,Co-efficient of utilization

1. Maintenance factor,Absorption
factor,Reflection factor,
Co-efficient of utilization
Presented by
Suhail TP
MES Collage of Engineering
ELECTRICAL SYSTEM DESIGN 1

2. Maintenance factor
• In lighting calculations, ratio of illumination of a
light source or lighted surface at a given time to
that of initial illumination.
• This factor is used to determine depreciation of a
lamp or a reflective surface over a period of time.
• MF:Ratio of illuminance at end of maintenance
period to initial illuminance.
ELECTRICAL SYSTEM DESIGN 2

3. Maintenance factor(contd)…
• Dust & dirt of surroundings may get deposited
on light fittings & hence deteriorate lamp
efficiency.
• If regular periodic cleaning is adopted &
assuming good atmospheric conditions ,value
of maintenance factor may be taken as 0.8
ELECTRICAL SYSTEM DESIGN 3

4. Maintenance factor(contd)…
• For dusty & dirty atmosphere, factor may be as
low as 0.4.
• Another term depreciation factor is also used
which is reciprocal of maintenance factor.
• Depreciation factor=1/(maintenance factor)
ELECTRICAL SYSTEM DESIGN 4

5. Reflection Factor & Absorption factor
• Whole of the light incident on a reflecting
surface is not reflected.
• Some portion of it is absorbed by the surface.
• The ratio of reflected light to incident light is
called reflection factor.
• The ratio of absorbed light to incident light is
called absorption factor.
ELECTRICAL SYSTEM DESIGN 5

6. Co-efficient of utilization
• The lumen output of sources is not fully
utilized at work place.
• Part of it is lost in fittings.
• Some part is directed to walls & ceiling which
may be absorbed or reflected.
• This is taken into account by a factor known as
co-efficient of utilization
ELECTRICAL SYSTEM DESIGN 6

7. Co–efficient of Utilization(contd…)
• A surface to be illuminated receive light either
directly from lamps or reflected from ceiling & walls
or both.
• In this case, total flux reaching the surface will
never be equal to flux emitted by lamp, due to
absorption by reflectors, ceiling & walls.
Utilization factor = lumens reaching at the working place
total lumens emitted by the source
Usually it varies from 0.5 to 0.8.
ELECTRICAL SYSTEM DESIGN 7

8. Co–efficient of Utilization(contd…)
Co-efficient of utilization depends on
• Lumen output of fitting
• Size & shape of room
• Reflection factors of walls & ceiling
• Height of ceiling
• Arrangement of fittings.
ELECTRICAL SYSTEM DESIGN 8

9. Calculation of Illumination
푁 =
퐸. 퐴
푂. 퐶푈. 푀퐹
Where
• N=Number of fittings needed.
• E=Required Illumination(lux).
• A=Working area(sq.m)
• O=Luminous flux produced per lamp(lumens)
• CU=Co-efficient of utilization.
• MF=Maintenance factor.
ELECTRICAL SYSTEM DESIGN 9

10. THANK YOU
ELECTRICAL SYSTEM DESIGN 10