Space light fixtures to provide uniform distribution and illumination of roadways and sidewalks. Consider the locations of obstruction such as trees or billboards.
Height. Standard poles for sidewalks and bike facilities are 4.5–6 m. Light poles for roadbeds vary according to the street typology and land use. In most contexts, standard heights for narrow streets in residential, commercial, and historical contexts are between 8–10 m. Taller poles between 10 m and 12 m are appropriate for wider streets in commercial or industrial areas.
Spacing. The spacing between two light poles should be roughly 2.5–3 times the height of the pole. Shorter light poles should be installed at closer intervals. The density, speed of travel, and the type of light source along a corridor will also determine the ideal height and spacing.
Light Cone. The light cone has roughly the same diameter as the height of the fixture from the ground. The height will, therefore, determine the maximum suggested distance between two light poles to avoid dark areas.
1- Calculate Distance between each Street Light Pole
Example
Calculate Distance between each streetlight pole having the following Details
- Road Details: The width of the road is 11.5 Feet.
- Pole Details: The height of the Pole is 26.5 Feet.
- The luminaire of each Pole: Wattage of Luminaries is 250 Watt, Lamp OutPut (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=(LL*CU*LLD*LDD) / Eh*W
- 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 the defined value. Spacing between each Pole is 75 Feet.
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 the road is 7 Meters. The distance between each Pole (D) is 50 Meters.
- 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.
- The 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 watts per Square Meter.
