Calculate No of Lighting Fixtures / Lumen for Indoor Lighting
April 8, 2014 62 Comments
 An office area is 20meter (Length) x 10meter (width) x 3 Meter (height). The ceiling to desk height is 2 meters. The area is to be illuminated to a general level of 250 lux using twin lamp 32 watt CFL luminaires with a SHR of 1.25. Each lamp has an initial output (Efficiency) of 85 lumen per watt. The lamps Maintenance Factor (MF) is 0.63 ,Utilization Factor is 0.69 and space height ratio (SHR) is 1.25
Calculation:
Calculate Total Wattage of Fixtures:
 Total Wattage of Fixtures= No of Lamps X each Lamp’s Watt.
 Total Wattage of Fixtures=2×32=64Watt.
Calculate Lumen per Fixtures:
 Lumen per Fixtures = Lumen Efficiency(Lumen per Watt) x each Fixture’s Watt
 Lumen per Fixtures= 85 x 64 = 5440Lumen
Calculate No’s of Fixtures:
 Required No of Fixtures = Required Lux x Room Area / MFxUFx Lumen per Fixture
 Required No of Fixtures =(250x20x10) / (0.63×0.69×5440)

Required No of Fixtures =21 No’s
Calculate Minimum Spacing Between each Fixture:
 The ceiling to desk height is 2 meters and Space height Ratio is 1.25 so
 Maximum spacing between Fixtures =2×1.25=2.25meter.
Calculate No of Row Fixture’s Row Required along with width of Room:
 Number of Row required = width of Room / Max. Spacing= 10/2.25
 Number of Row required=4.
Calculate No of Fixture’s required in each Row:
 Number of Fixture Required in each Row = Total Fixtures / No of Row = 21/4
 Number of Fixture Required in each Row = 5 No’s:
Calculate Axial Spacing between each Fixture:
 Axial Spacing between Fixtures = Length of Room / Number of Fixture in each Row
 Axial Spacing between Fixtures =20 / 5 = 4 Meter
Calculate Transverse Spacing between each Fixture:
 Transverse Spacing between Fixtures = width of Room / Number of Fixture’s row
 Transverse Spacing between Fixtures = 10 / 4 = 2.5 Meter.
Conclusion:
 No of Row for Lighting Fixture’s= 4 No
 No of Lighting Fixtures in each Row= 5 No
 Axial Spacing between Fixtures= 4.0 Meter
 Transverse Spacing between Fixtures= 2.5 Meter
 Required No of Fixtures =21 No’s
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