Calculator
Enter your driveway and fixture details. The calculator uses two spacing checks: a lux-based planning method and a spacing-to-mounting-height rule.
Example data table
These sample scenarios illustrate how spacing and fixture count change with driveway size and target lighting level.
| Length (m) | Width (m) | Target (lux) | Fixture (lm) | Layout | Mount height (m) | Typical spacing (m) | Typical fixtures |
|---|---|---|---|---|---|---|---|
| 12 | 3 | 10 | 700 | One-side | 0.6 | 2.0–2.6 | 6–8 |
| 18 | 3.5 | 15 | 900 | Two-side | 0.8 | 2.5–3.2 | 10–14 |
| 30 | 4 | 20 | 1200 | Two-side | 1.0 | 3.0–4.0 | 16–22 |
| 25 | 3 | 8 | 600 | Centerline | 0.7 | 2.8–3.8 | 8–10 |
Actual results depend on optics, glare control, and site reflectance.
Formula used
1) Effective lumens per fixture
Lm_eff = Lm_fixture × UF × MF
2) Lux-based spacing (planning estimate)
Assuming each fixture “serves” a rectangular area of S × W_eff on one row.
E ≈ (Lm_eff × Overlap) / (S × W_eff) ⇒ S_lux = (Lm_eff × Overlap) / (E × W_eff)
3) Spacing-to-mounting-height rule
S_smh = SMH × H_mount
4) Recommended spacing
S_recommended = min(S_lux, S_smh)
5) Fixture count check (lumens method)
Lm_total_required = (E × Area) / (UF × MF)
How to use this calculator
- Measure driveway length and width in meters.
- Pick a target average illuminance in lux.
- Enter fixture lumens and optional wattage.
- Select a layout: one-side, two-side, or centerline.
- Set mounting height and SMH ratio for uniformity.
- Adjust UF and MF to match real conditions.
- Press Calculate to see spacing, count, and placement.
- Download CSV or PDF for sharing and marking.
Professional article
1) Why spacing matters for driveways
Driveways are narrow circulation routes where visibility, edge definition, and glare control matter. Uniform spacing reduces dark gaps that hide curbs, steps, and vehicles. For residential work, many projects aim for consistent guidance lighting rather than stadium brightness, so spacing decisions often dominate perceived safety.
2) Typical target illuminance ranges
Planning targets commonly fall between 5 and 20 lux for guidance, with higher values used where turning, reversing, or pedestrian activity increases. The calculator uses your chosen lux target as an average design goal. If the driveway includes ramps, gates, or crossings, a modest uplift in target lux can improve recognition.
3) Fixture lumens and practical output
Lumens describe total light leaving the fixture, but not all of it reaches the pavement. A 600–1200 lumen unit is typical for compact driveway lights, while brighter products are used for tall poles. Higher lumens can increase spacing, but beam control must keep light on the driveway, not in neighbors’ windows.
4) Utilization and maintenance factors
The utilization factor (UF) captures optical efficiency and how much light actually lands on the target area. Maintenance factor (MF) accounts for lens dirt, aging, and lumen depreciation. A planning set such as UF 0.45–0.65 and MF 0.70–0.90 is common, and conservative values prevent under-lighting over time.
5) Mounting height and SMH guidance
Spacing-to-mounting-height (SMH) is a quick uniformity control. Lower fixtures usually require shorter spacing to avoid bright pools and dark gaps. Many driveway layouts work well with SMH around 2.5 to 4.0, depending on beam angle. The calculator compares SMH spacing with the lux method and recommends the smaller value.
6) Layout choices and width coverage
Two-side layouts improve edge definition and reduce shadows from parked vehicles, but they increase fixture counts. One-side or centerline layouts reduce hardware while relying on wider distribution. The calculator assigns an effective width per row and lets you adjust coverage and overlap factors to reflect beam spread, offsets, and real-site constraints.
7) Energy and quick load estimates
Total power equals fixture wattage times fixture count, which helps early electrical planning. For example, 12 W fixtures at 14 units imply about 168 W connected load. Pairing spacing with controls such as photocells, dimming, or curfews can reduce consumption while maintaining guidance levels during peak use times.
8) Field checks to validate the plan
After installation, validate with a simple lux meter or smartphone sensor as a rough check. Confirm uniformity along the edges and at turning points, then adjust aiming and tilt before changing spacing. Keep end offsets consistent to avoid bright hotspots at garage doors or gates and to preserve an even visual rhythm.
FAQs
1) What lux value should I choose for a home driveway?
Many residential driveways use about 5–15 lux for guidance. Choose higher values for frequent pedestrian traffic, turning areas, or security preferences. Always balance brightness with glare and neighbor spill control.
2) Why does the calculator use UF and MF?
UF estimates how much emitted light reaches the driveway surface. MF accounts for dirt and aging losses. Together, they reduce optimistic assumptions and keep spacing and counts realistic over the service life.
3) How does mounting height affect spacing?
Higher mounting generally allows wider spacing with smoother distribution, while low fixtures create bright pools and need tighter spacing. Use SMH values around 2.5–4.0 as a starting range and tune based on optics.
4) Should I pick one-side or two-side lighting?
Two-side improves edge definition and shadow control, especially with parked cars. One-side reduces hardware and wiring but may create darker opposite edges. Select based on driveway width, landscape constraints, and desired visual symmetry.
5) What does the overlap factor do?
Overlap increases the lux-based spacing allowance by assuming adjacent beams overlap to smooth dark gaps. Set it near 1.0 for neutral behavior. Use higher values only when optics and aiming clearly provide strong overlap.
6) Why is there an end offset input?
End offsets keep fixtures away from the driveway ends to avoid glare hotspots at doors and gates and to protect luminaires from impacts. They also produce a cleaner, repeatable pattern when using evenly spaced placements.
7) Are the lux results exact?
No. The lux estimate is a planning average based on simplified area coverage assumptions. For final design, confirm with manufacturer photometric files, site reflectance, and a quick field measurement after installation.
Use spacing plans to improve safety and comfort.