Calculate No of Street Light Poles

Typical Calculation of Road Lighting:

  •  Luminaries are properly selected and mounted on a location most feasible and effective with minimum cost. For a 230 volts system, a voltage drop of 5% is allowed although in extreme cases 15% voltage drop is sometimes tolerated.  3
  • Street illumination level in Lux (E)=(Al x (cu x mf)) / (w x d)
  • E = The illumination in Lux
  • w = Width of the roadway
  • d = Distance between luminaries
  • cu = Coefficient of utilization. Which is dependent on the type of fixture, mounting height, width of roadway and the length of mast arm of outreach?
  • Al = Average lumens, Al = (E x w x d) / Cu x mf
  • The typical value of Al is
  • 20500 lumens for 400 watts
  • 11500 lumens for 250 watts
  • 5400 lumens for 125 watts
  • The value of Al varies depending upon the type of lamp specified.
  • mf : It is the maintenance factor (Normally 0.8 to 0.9)

 (1) Calculate Lamp watt for street Light Pole:

  • Calculate Lamp Lumen for street Light Pole having Road width of 7 meter, distance between two Pole is 50 meter, Maintenance factor is 0.9, Coefficient of utilization factor is 0.29, light pedestrian traffic is medium and Vehicular traffic is very light and Road is concrete road.
    From Above table Recommended of illumination (E) in Lux is 6.46 per sq. meter.
    w = 7.00 meters , d = 50 meters , mf = 0.9, cu = 0.29
    To decide Lamp Watt It is necessary to calculate Average Lumens of Lamp (Al).
  • Average Lumen of Lamp (Al)=(E x w x d) / Cu x mf
  • Al=(6.46x7x50)/(0.29×0.9)= 8662.83 Average lumen
    Lamp lumen of a 250 watts lamp is 11,500 lm which is the nearest value to 8662.83 lumen. Therefore, a 250 watts lamp is acceptable.
    Let’s Computing for the actual illumination E for 250 Watt Lamp
  • Illumination (E)=(Al x (cu x mf)) / (w x d)
  • E= (11500×0.29×0.9) / (7×50) = 8.57 lumen per sq meter.
    Actual illumination (E) for 250 Watt is 8.57 lumen per sq meter which is higher than recommended illumination (E) 6.46.
  • Hence 250 watt gives adequately lighting.

 (2) Calculate Spacing between two Light Poles:

  • Calculate Space between Two Pole of Street Light having Fixture Watt is 250W , Lamp output of the Lamp (LL) is 33200 lumens , Required Lux Level (E) is 5 lux , Width of the road(W) = 11.48 feet (3.5 M),Height of the pole (H) = 26.24 feet (8 M) ,Coefficient of utilization (CU) = 0.18, Lamp Lumen Depreciation Factor (LLD) = 0.8 ,Luminaries dirt Depreciation Factor (LDD) = 0.9
  • Luminaries Spacing (S) = (LLxCUxLLDxLDD) / (ExW)
  • Luminaries Spacing (S) = (33200×0.18×0.9×0.8) / (5×11.48)
  • Luminaries Spacing (S) = 75 feet (23 Meters)

 (3) Calculation of the allowed illumination time:

  • The allowed illumination time in hours T = k.t.1000/E.
  • Where: k = extension factor
  • t = permissible time in hours at 1000 lux, unfiltered daylight
  • E = luminance (lx)


Extension Factor
Lamp Extension Factor
Incandescent lamps, 2.7 to 3.2
Halogen reflector lamps 2.5 to 3.5
Halogen capsules 2.5 to 3.5
High-pressure metal-halide 1.1 to 2.1
High-pressure sodium lamps 4
Fluorescent lamps 1.9 to 2.7


  • Example:
  • In sunlight (100000 lux) and extension factor 1: The permissible illumination time (T) =1 x 70 x 1000/100 000 = 0.7 hour.
  • In halogen light (200 lux) and extension factor 2.3: The permissible illumination time (T) = 2.3 x 70 x 1000/200 = 805 hours.
  • In UV-filtered halogen light (200 lux) and extension factor 3.5: The permissible illumination time (T) = 3.5 x 70 x 1000/200 = 1225 hours.

 (4) Calculate Uniformity Ratio:

  • Once luminaries spacing has been decided It is necessary to check the uniformity of light distribution and compare this value to the selected lighting
  • Uniformity Ratio ( UR) = Eav /Emin
  • Eav= average maintained horizontal luminance
  • Emin = maintained horizontal luminance at the point of minimum illumination on the pavement

 (5) Energy Saving Calculations:

  • At a simplistic level, the cost of running a light is directly related to the wattage of the globe plus any associated ballast or transformer. The higher the wattage, the higher the running cost and it is a straightforward calculation to work out the running cost of lamp over its lifetime:
  • Running cost = cost of electricity in $/kWh x wattage of lamp x lifetime in hours.

 Calculate Lux Level for Street Lighting

  • The Average Lux Level of Street Light is measured by 9 point method. Make two equal quadrants between two Street light poles. on the lane of light poles( one side pole to road).
  • We have 3 points P1,P2 and P3 under the light pole then P4 & P7 are points opposite pole 1 or Point P3 same is applicable for P6 and P9 for Pole 2.
  • The average lux = [(P1+P3+P7+P9)/16]+[(P2+P6+P8+P4)/8]+[P5/4]


About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

28 Responses to Calculate No of Street Light Poles

  1. Carlos Restrepo says:

    Very intesresting and simple. thanks.

  2. goutam says:

    Plz dehumidifier calculation sheet make and sent me.

  3. Atta Khan says:




  4. Ashish Lotake says:

    Thanks for forwarded notes. also forwarded the 33kv line deatils like conductor size,materials list and etc……..

  5. darwin says:

    sir i couldn’t see the table of Recommended Illuminations like what you have said in your example. May you send it to me. thanks.

  6. amrendra kumar says:

    very interesting….)))

  7. uday raj maurya says:

    Required all power & control cable current calculation chart.

  8. mohamed says:

    please i want to know more about 9-points method and other methods like 12-points method and more

  9. levanluong says:

    very interesting. thanks sr!

  10. Rushil says:

    i am a student and i do not understand the need for an outreach in a lamp post can you explain

  11. pramod kumar chaturvedi says:

    Required out door street light lux calculations chart (1) pole mounting height 7.922 mtr (2) pole distance 43 mtr (3) boom length 1 mtr (4) boom angle 1o dig (5) arrangement double row with offset (6) luminaire wattage 172 w (7) luminous flux (lamps) 17000 lm (8) Road width 7 mtr (9) Required Lux Level mim 20 lux (10) light loss factor 0.80 please sand thanks

  12. angelasv308 says:

    DEAR SIR ,,

  13. eric says:

    good day sir i have a problem to calculate the luminous flux of a lamp wattage of 250watts,height of pole 7.6m, spacing between poles 40m and a mounting height of 1.5 please can u help me out

  14. SAJIN says:

    Dear Sir,\
    Thanks for the details and is very helpful, My doubt is why this calculation vales not related to pole height? How we can determine pole height for a out door lighting project? How we can determine wattage for a fixture which is placed at high level area.
    Please reply

  15. To find the distance between two street light pole of 9 meter height having fitting of 250 watt high pressure mercury vapour

  16. Varad Enterprises says:

    Hello Jignesh Sir,
    Can you please guide me how to calculate the voltage drop in designing the street lighting. Want to determine the size of the cable to be used for the highway road where 120W LED Street lighting is to be used. Span between the pole is assumed to be 20-25 m and the lighting poles are in the middle of the 100 m road

  17. simple but u didn’t considered pole mounting height??
    what is the standard street light height??

  18. sansereyvathna says:

    where is table Recommended of illumination? I can’t see it.

  19. sandeep ji says:

    dear sir / madam

    this is good but practical data is not mach , utilization and multiplication factor how to decide , any one can give me right solution for street light pole , wattage , lux any formula please explain me ,
    sandeep kumar

  20. getnet says:

    pleace notify standards for home installation via my e mail.

  21. Kashmira says:

    Dear Sir,

    Please guide me to understand how to calculate following constant values you used in calculating spacing between two light poles =
    1.Coefficient of utilization (CU) = 0.18,
    2.Lamp Lumen Depreciation Factor (LLD) = 0.8 ,
    3.Luminaries dirt Depreciation Factor (LDD) = 0.9
    are these values same in every type of lamp calculation or do they change everytime with different lamp?

  22. Mel says:

    where is the computation of the actual number of street light poles? you didn’t included it in your computation. Thank you

  23. suresh says:

    Dear sir,
    please clarify this nine point method is taken form which standards,and how the formula derived.

    please guide.

    suresh Kumar patnala

  24. suresh says:

    Please guide me how this nine point method derived for lux measurement ,and from which standards.

    Please help,
    suresh kumar

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