| Case | Units | MH | Width | Target | Lumens | CU | LLF | Arrangement | S/MH |
|---|---|---|---|---|---|---|---|---|---|
| Urban collector | Metric | 9 m | 10 m | 15 lux | 20,000 lm | 0.35 | 0.80 | Staggered | 3.5 |
| Arterial (paired poles) | Metric | 12 m | 16 m | 20 lux | 28,000 lm | 0.40 | 0.75 | Opposite | 3.2 |
| Residential street | Imperial | 25 ft | 28 ft | 1.0 fc | 12,000 lm | 0.30 | 0.80 | One-side | 3.8 |
This calculator uses a practical lumen-method estimate for roadway lighting, treating each station segment as a rectangular area. It then applies an optional spacing-to-mounting-height (S/MH) limit for uniformity planning.
| Average illuminance | E ≈ ( Φ × CU × LLF ) / ( W × S ) |
|---|---|
| Spacing from lumen method | S ≈ ( Φ × CU × LLF ) / ( E × W ) |
| Uniformity cap (optional) | Scap = (S/MH)max × MH |
| Arrangement assumption | Opposite layout uses two poles per station; others use one. |
- Pick units, then enter mounting height and lit roadway width.
- Set the target average illuminance for the roadway class.
- Enter delivered lumens, CU, and LLF for your luminaire.
- Choose the pole arrangement and luminaires per pole.
- Optionally keep the S/MH limit enabled for uniformity.
- Click Calculate spacing to view results above the form.
- Use CSV or PDF buttons to save outputs for your report.
1) Purpose and planning context
Streetlight spacing affects visibility and the number of poles required. This calculator supports early design by translating lighting targets into a practical spacing recommendation, plus pole counts and energy estimates.
2) Data inputs that most influence spacing
The method uses mounting height, lit roadway width, target average illuminance, and delivered lumens. Two correction factors refine results: coefficient of utilization (CU) estimates how much light reaches the pavement, while light loss factor (LLF) accounts for depreciation and dirt.
Common planning ranges are CU 0.25–0.55 and LLF 0.70–0.85. As an illustration, a 10 m roadway, 15 lux target, 20,000 lm luminaire, CU 0.35, and LLF 0.80 yields roughly 37 m spacing for one pole per station, before any uniformity cap.
3) Arrangement choices along the roadway
Layout affects how many luminaires contribute at each station. One-side, staggered, and median layouts assume one pole per station. Opposite (paired) layout assumes two poles per station, increasing contributing lumens and improving distribution on wider roads.
4) Interpreting spacing and quantities
The calculator first computes a lumen-method spacing from your illuminance target and width. It can also apply an S/MH cap, limiting spacing to a selected spacing-to-mounting-height ratio. The smaller value becomes the recommended spacing, and the governing reason is shown.
Using project length, the tool estimates stations, total poles, and luminaires. It also computes connected load from luminaire wattage and estimates annual energy using hours-per-night and 365 days. Use these outputs to compare lumen packages versus closer spacing.
5) Professional checks before final design
Use results to compare options, not to finalize compliance. Confirm roadway class criteria, uniformity expectations, glare control, intersections, and utility conflicts. Validate with manufacturer photometric files and local standards, then adjust spacing near curves, junctions, and crossings.
1) What does CU mean?
CU is the fraction of lumens that effectively reach the pavement. It varies with optics, mounting, and geometry. Higher CU generally increases the calculated spacing for the same target illuminance.
2) Why include LLF?
LLF represents expected light reduction over time from depreciation and dirt. Using a realistic LLF prevents spacing that looks acceptable on day one but underperforms later.
3) Should I always use the S/MH limit?
For planning, yes. The S/MH cap is a fast uniformity proxy that avoids excessive spacing and reduces the risk of dark gaps, especially on wider roads.
4) How does “Opposite (paired)” affect results?
It assumes two poles at each station, one on each side. That increases lumens per station and may increase spacing, but total pole count can also rise depending on the final station spacing.
5) What target illuminance should I enter?
Use the value specified by your local roadway class and standard. If you are screening options, start conservatively and refine after reviewing jurisdictional guidance.
6) Does this replace full photometric design?
No. It is a preliminary lumen-method estimate with an optional spacing cap. Final design should be verified using photometric files and compliance checks.
7) Why can real spacing differ on site?
Setbacks, trees, utilities, intersections, curves, glare limits, and local rules often require adjustments. Use the recommendation as a baseline, then tune spacing to field constraints.