To calculate the required light for street lighting, consider factors such as road width, pole height, spacing, and lumen output. Using industry standards, the proper illuminance level ensures safety and efficiency.
Street lighting is essential for urban safety and visibility. However, determining the right amount of light requires a structured approach. Engineers and city planners use specific formulas and standards to ensure proper illumination levels for different road types.
Key Factors in Calculating Street Lighting Requirements
1. Road Type and Classification
Different roads require different illumination levels based on traffic flow and pedestrian activity.
Highways need higher luminance levels than residential streets. Road classification helps determine the required lighting intensity.
Road types influence lighting design. Here’s a general guideline:
| Road Type | Typical Illuminance (Lux) | Example |
|---|---|---|
| Highways | 20-50 | Major expressways |
| Main Roads | 15-30 | City streets, arterial roads |
| Residential Roads | 5-15 | Neighborhood streets |
| Pedestrian Paths | 2-10 | Walkways, parks |
2. Pole Height and Spacing
The height and spacing of street light poles affect the distribution of light.
Higher poles provide broader coverage, but proper spacing prevents dark spots or excessive overlap.
Common pole height and spacing recommendations:
| Pole Height (m) | Spacing (m) |
|---|---|
| 6-8 | 15-20 |
| 9-12 | 25-35 |
| 12-15 | 35-45 |
Calculation Formula:
The ideal pole spacing is calculated using:
S = 3 \times H
Where:
- ( S ) = spacing between poles
- ( H ) = height of the pole
3. Lumen Output and Light Distribution
Lumen output determines how much light a fixture emits.
The total lumens required depend on road width, pole spacing, and the number of fixtures per pole.
To calculate the total lumens required:
L = E \times A
Where:
- ( L ) = total lumens required
- ( E ) = required illuminance (lux)
- ( A ) = area to be illuminated (m²)
For example, if a road section of 10m width and 50m length requires 20 lux:
L = 20 \times (10 \times 50) = 10,000 \text{ lumens}
4. Light Uniformity and Glare Control
Uniform lighting reduces dark patches and enhances visibility.
A uniformity ratio (U) of at least 0.4 ensures consistent lighting across the road.
Glare control is also important. Using cutoff fixtures and proper beam angles prevents excessive brightness that could blind drivers or pedestrians.
5. Energy Efficiency and LED Selection
LED lights are the preferred choice for street lighting due to their efficiency and long lifespan.
Choosing the right wattage ensures adequate brightness while minimizing energy costs.
Typical LED wattage recommendations:
| Road Type | Recommended LED Wattage |
|---|---|
| Highways | 120W - 250W |
| Main Roads | 80W - 150W |
| Residential | 30W - 80W |
| Walkways | 10W - 40W |
Step-by-Step Guide to Calculate Street Lighting
- Identify the road type – Determine the required illuminance (lux) level.
- Measure the road dimensions – Width and length of the area to be lit.
- Decide pole height and spacing – Based on standard guidelines.
- Calculate total lumens required – Using the formula ( L = E \times A ).
- Choose the appropriate LED wattage – Based on energy efficiency and required brightness.
- Ensure uniformity and glare control – Use proper fixture placement.
Conclusion
Proper street lighting calculation ensures safety, energy efficiency, and optimal visibility.
By considering factors such as road type, pole height, spacing, and lumens, city planners can design effective street lighting systems that enhance nighttime safety while reducing operational costs.
