Street Lighting Spacing Calculator

Inputs

Road length *

m

Total length you are lighting.

Road width *

m

Paved width or effective lit width.

Mounting height *

m

Height of luminaire above roadway.

Luminaire output *

lm

Initial lumens per fixture.

Coefficient of utilization *

0–1

Fixture and layout efficiency factor.

Light loss factor *

0–1

Accounts for dirt, aging, and temperature.

Target average illuminance *

lux

Design target for the roadway.

Arrangement * Single-side Opposite Staggered

Controls how many fixtures serve each segment.

Max spacing ratio (S/H) *

S/H

Use vendor guidance for better uniformity.

Calculate spacing Reset form

This tool gives planning-level spacing. Verify with photometric layouts for final design.

Example data table

Formula used

How to use this calculator

1. Enter road length and road width based on your corridor.
2. Choose mounting height using your pole and arm setup.
3. Type the luminaire output, then set CU and LLF.
4. Set your target illuminance and pick an arrangement.
5. Enter a max spacing ratio from the luminaire guidance.
6. Press Calculate spacing to view results above.
7. Use CSV or PDF downloads for records and sharing.

Notes for professional use

• This calculator is intended for early design and budgeting.
• Coefficient of utilization varies by optics and surroundings.
• Light loss factor depends on maintenance cycles and environment.
• Confirm roadway class targets with your local standards.
• Run photometric checks for glare and uniformity verification.

Lighting performance drivers

Street lighting spacing starts with lumens, roadway width, and arrangement. A single-side layout serves one lane zone per segment, while opposite or staggered layouts effectively double contributing fixtures. For opposite and staggered patterns, the calculator assumes two luminaires share each spacing segment along the alignment. Wider pavements dilute light, so spacing should be justified with inputs and units. In the lumen method, spacing increases when useful lumens rise.

Selecting target illuminance

Choose an average lux target based on road class, conflict points, and pedestrian activity. Residential streets often need lower averages, while collectors and arterials demand higher levels and tighter uniformity. Typical planning targets can range from 5 to 20 lux. Use higher values near crossings and bus stops, then model separate zones if needed. When you raise the lux target, allowable spacing drops almost proportionally.

Using CU and LLF correctly

Coefficient of utilization represents how much emitted light reaches the roadway. It depends on luminaire distribution, mounting geometry, and surroundings. Light loss factor accounts for dirt, lumen depreciation, and ambient conditions. Conservative projects use lower LLF to reflect longer maintenance cycles. Record CU and LLF sources to support design reviews and audits.

Spacing ratio and mounting height

Uniformity guidance is often expressed as a maximum spacing-to-height ratio. Increasing mounting height can permit larger spacing, but it may change glare, backlight, and spill control. If the ratio limit governs, the recommended spacing is height multiplied by the ratio. If illuminance governs, spacing is driven by the lumen method. Verify ratio guidance against photometric files for the selected fixture.

Turning spacing into quantities

Once spacing is selected, estimate segments by dividing road length by spacing and rounding up. Single-side layouts typically need one pole per segment, while opposite or staggered layouts need two. Convert poles to circuits by grouping consecutive poles per feeder and allowing spare capacity. Add end corrections near intersections, curves, or transitions, and verify final layouts with photometric calculations before construction.

FAQs

Can I use wattage instead of lumens?

Convert to lumens using the fixture’s rated efficacy or manufacturer lumen output. Wattage alone is not enough because optics and efficacy vary widely. Always prefer tested initial lumens from the product data sheet.

How do I pick a coefficient of utilization value?

Use photometric reports or roadway lighting tables for the selected luminaire and mounting geometry. If you do not have a report, start with a conservative planning value and refine it during detailed design.

Why does opposite or staggered layout change spacing?

Those layouts place fixtures on both sides of the road, so more light contributes to each roadway segment. The calculator models this by increasing the effective lumens serving each spacing interval.

What spacing-to-height ratio should I enter?

Use the manufacturer’s recommended maximum S/H for your luminaire and distribution. If a local standard specifies a tighter limit, follow the standard. Lower ratios generally improve uniformity but raise pole counts.

Are the pole counts final for procurement?

They are planning estimates based on straight segments and uniform spacing. Add poles for intersections, curves, and transitions, and coordinate with electrical design, foundations, clear zones, and utility conflicts before ordering.

When should I move beyond this calculator?

Use a full photometric layout when finalizing fixture selection, checking uniformity and glare, or documenting compliance. Detailed modeling is also important for complex geometry, medians, multi-lane roads, or sensitive adjacent areas.