Calculate No of Lighting Fixtures / Lumen for Indoor Lighting
April 8, 2014 13 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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Thanks for your great work ,,,,,,, best regards
Thanks for the blog.
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Found very correct . This is a thumb rule type of design – and it is the best approach for the electrical engineers like us . A really thankful Job . Here I want to request you to discuss the importance of Polar Curves of verious lamps for illumination design if possible . Thanks .
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great work. concise and useful.
thanks for useful article, and sir please load standard lux level chart and please explain lumen per watt, U.F, M.F AND SHR
Thanking you,
Helping a lot with ur kno wledge
jignesh paramer ,your material is very useful to me ,plz suggest me design courses for electrical.I want to builtup career in design.
Could you explain how did you take “total fixtures=21″
For your Reference:
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 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
Can u please refer me the book where i can completely know about lighting design both indoor and outdoor, kindly help me in this matter