street lights

Technically, the distance between two street lights should be 29 meters. This is defined by calculations of pole heights and other factors. Intention of keeping a standard distance is to maintain good illumination on streets. But at many places in PCB the distance between two lamps is as much as 50 meters.

Street light pole distance calculation:

(1) Calculate Distance between each Street Light Pole:
Example: Calculate Distance between each streetlight pole having following Details,

Road Details: The width of road (w) is 11.5 Foot.
Pole Details: The height of Pole is 26.5 Foot.
Luminaire of each Pole: Wattage of Luminaries is 250 Watt, Lamp Out Put (LL) is 33200 Lumen, Required Lux Level (Eh) is 5 Lux, Coefficient of Utilization Factor (Cu) is 0.18, Lamp Lumen Depreciation Factor (LLD) is 0.8, Lamp Lumen Depreciation Factor (LLD) is 0.9.
Space Height Ratio should be less than 3.
Calculation:

Spacing between each Pole=(LLCULLDLDD) / EhW
Spacing between each Pole=(33200×0.18×0.8×0.9) / (5×11.5)
Spacing between each Pole= 75 Foot.
Space Height Ratio = Distance between Pole / Road width
Space Height Ratio = 3. Which is less than define value.
Spacing between each Pole is 75 Foot.
(2) Calculate Street Light Luminaire Watt:
Example: Calculate Streetlight Watt of each Luminaire of Street Light Pole having following Details,

Road Details: The width of road (w) is 7 Meter. Distance between each Pole (D) is 50 Meter.
Required Illumination Level for Street Light (L) is 6.46 Lux per Square Meter. Luminous efficacy is 24 Lumen/Watt.
Maintenance Factor (mf) 0.29, Coefficient of Utilization Factor (Cu) is 0.9.
Calculation:

Average Lumen of Lamp (Al) = 8663 Lumen.
Average Lumen of Lamp (Al) =(LxWxD) / (mfxcu)
Average Lumen of Lamp (Al)= (6.46x7x50) / (0.29×0.9)
Average Lumen of Lamp (Al)=8663 Lumen.
Watt of Each Street Light Luminar = Average Lumen of Lamp / Luminous efficacy
Watt of Each Street Light Laminar = 8663 / 24
Watt of Each Street Light Luminaire = 361 Watt
(3) Calculate Required Power for Street Light Area:
Example: Calculate Streetlight Watt of following Street Light Area,

Required Illumination Level for Street Light (L) is 6 Lux per Square Meter.
Luminous efficacy (En) is 20 Lumen per Watt.
Required Street Light Area to be illuminated (A) is 1 Square Meter.
Calculation:

Required Streetlight Watt = (Lux per Sq.Meter X Surface Area of Street Light) / Lumen per Watt.
Required Streetlight Watt = (6 X 1) / 20.
Required Streetlight Watt = 0.3 watt per Square Meter.

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