Maintenance factor,Absorption factor,Reflection factor,

Co-efficient of utilization

Presented by

Suhail TP

MES Collage of Engineering

1ELECTRICAL SYSTEM DESIGN

Maintenance factor

• In lighting calculations, ratio of illumination of alight source or lighted surface at a given time tothat of initial illumination.

• This factor is used to determine depreciation of alamp or a reflective surface over a period of time.

• MF:Ratio of illuminance at end of maintenanceperiod to initial illuminance.

2ELECTRICAL SYSTEM DESIGN

Maintenance factor(contd)…

• Dust & dirt of surroundings may get depositedon light fittings & hence deteriorate lampefficiency.

• If regular periodic cleaning is adopted &assuming good atmospheric conditions ,valueof maintenance factor may be taken as 0.8

3ELECTRICAL SYSTEM DESIGN

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)

4ELECTRICAL SYSTEM DESIGN

Reflection Factor & Absorption factor

• Whole of the light incident on a reflectingsurface is not reflected.

• Some portion of it is absorbed by the surface.

• The ratio of reflected light to incident light iscalled reflection factor.

• The ratio of absorbed light to incident light iscalled absorption factor.

5ELECTRICAL SYSTEM DESIGN

Co-efficient of utilization

• The lumen output of sources is not fullyutilized at work place.

• Part of it is lost in fittings.

• Some part is directed to walls & ceiling whichmay be absorbed or reflected.

• This is taken into account by a factor known asco-efficient of utilization

6ELECTRICAL SYSTEM DESIGN

Co–efficient of Utilization(contd…)

• A surface to be illuminated receive light eitherdirectly from lamps or reflected from ceiling & wallsor both.

• In this case, total flux reaching the surface willnever be equal to flux emitted by lamp, due toabsorption 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.

7ELECTRICAL SYSTEM DESIGN

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.

8ELECTRICAL SYSTEM DESIGN

Calculation of Illumination

𝑁 =𝐸. 𝐴

𝑂. 𝐶𝑈.𝑀𝐹Where

• 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

ELECTRICAL SYSTEM DESIGN 10

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