Planning street lighting for private roads cannot be based on pole height alone. For a straight road with regular pole locations, a preliminary screen of roughly 5 to 7 times the mounting height gives a starting concept, but the actual center-to-center spacing depends on the specific luminaire's photometric distribution, tilt, road width, and obstructions. Treat that ratio as a screening range, not a finished layout, and confirm the concept with an exact photometric model before buying poles or fixtures.
For example, a 30-foot mounting height would screen at roughly 150 to 210 feet of center-to-center spacing for a straight, continuous-lighting concept. That range only applies to a simple, obstruction-free layout; curves, grades, intersections, or varying road width require direct modeling instead of a single ratio.
Use 5–7× Mounting Height as a Screening Range—Not a Guarantee
A general historical roadway guideline places continuous-lighting luminaires at roughly 5 to 7 times mounting height for a straight, regular concept, but exact luminaire selection and a photometric analysis are still required to confirm luminance and uniformity results. Mounting height is the vertical distance from the ground to the luminaire's light source, and it is the only variable this ratio uses.
| Planning condition | Preliminary spacing treatment | Next decision |
|---|---|---|
| Straight road, regular poles, consistent width, no major obstructions | Screen center-to-center spacing at roughly 5-7× mounting height | Model the exact luminaire's photometry before treating the concept as buildable |
| Curves, grades, intersections, variable width, or obstructions | Do not apply a single ratio | Model each segment individually with actual site geometry |
The right-hand column matters more than the ratio itself. Even a straight-road concept that screens well on paper still needs the manufacturer's photometric file run against the real site before it becomes a purchase decision.
Why Dark Bands Appear Between Poles
A dark band is a gap or low point in useful ground coverage between two adjacent lighting patterns, and it comes from several site and equipment variables interacting, not from low lumen output by itself. Mounting height, spacing, road width, pole setback, the luminaire's distribution pattern, tilt, and obstructions all shape where the light actually lands. Diagnosing the band correctly points to the right fix.
- Repeated midpoint band along a straight run: usually points to a spacing-to-distribution mismatch. Check whether the selected spacing exceeds what the luminaire's photometric pattern can bridge at that mounting height.
- Edge-only band near one side of the road: often reflects pole setback or an asymmetric distribution that was not aimed for the actual road width.
- Transition band at a curve, grade change, or intersection: signals that a single repeated spacing assumption broke down where road geometry changed; that segment needs its own layout.
- Localized band near a tree, sign, or building: points to an obstruction blocking or redirecting the pattern, which a 2D spacing plan will not reveal.
Each of these has a different next check. A spacing/distribution mismatch calls for remodeling the layout with the exact photometric file, while a geometry or obstruction problem calls for segment-specific analysis rather than a wider or narrower ratio.
Collect the Inputs Before Setting Pole Locations
A workable layout starts with measured road and pole geometry paired with the exact luminaire's technical documents, not with lumens or wattage alone. Splitting the input packet into physical measurements and luminaire documentation keeps the process organized before any spacing decision is made.
Road and pole geometry
- Road width and the actual travel-surface boundaries, in feet
- Candidate pole coordinates or existing pole locations, plus setback from the road edge
- Mounting height at each pole, measured rather than assumed
- Grade changes, curves, and intersections along the route
- For retrofits, a note of every location where the existing layout differs from a new-installation plan
Luminaire and site documentation
- The exact IES/LDT photometric file and distribution data for the specific luminaire under consideration
- Permitted mounting orientation and tilt or aiming limits from the installation instructions
- Any lighting controls, such as dusk-to-dawn photocells or dimming, that affect the operating pattern
- Trees, buildings, neighboring properties, and other obstructions near the route
- Applicable local review requirements for the specific jurisdiction, since these vary by project and cannot be assumed from a general manual
Roadway design guidance illustrates this workflow well: it calls for manufacturer photometric information and calculation points rather than a spacing shortcut, plus a 3D representation wherever solid objects block a luminaire's contribution. That workflow is a useful planning example for private roads, not an automatic code requirement for them. Readers building a broader purchase timeline can also see our commercial lighting planning guide for how these inputs feed into fixture selection.
Evaluate a Proposed Spacing-to-Height Relationship
Judging a proposed spacing starts with the screening ratio, but the model of the actual luminaire and site is what decides whether the proposal is credible. Follow the same sequence for any straight-road concept before treating it as final.
- Record the proposed center-to-center spacing and the mounting height in feet, using consistent measurement points at each pole.
- Compare that spacing against the 5-7× mounting-height screening range as a first pass, not as approval.
- Load the exact luminaire's photometric file and model the real pole arrangement, road cross-section, grade, curves, and obstructions.
- Review the calculated point values and uniformity output along the roadway, not just total lumens or how bright the fixture looks.
- Revise the spacing, luminaire selection, or layout when the modeled result shows a dark band, and escalate to a qualified lighting designer when the site has curves, grades, or other complications the ratio cannot account for.
For a retrofit, this same sequence applies to existing poles: measure the current mounting height, spacing, and setback before assuming the new luminaire will match the old layout's performance. Our parking lot retrofit guide walks through the reuse-versus-redesign decision in more detail for that scenario.
Treat Luminaire Tilt as a Controlled Photometric Input
Tilt is a design variable to verify, not a shortcut for a spacing that already failed. Changing a luminaire's aim can move the useful part of its coverage pattern outward, but the same change can also increase near-horizontal light toward a property boundary, creating glare or light trespass.
- If the coverage pattern misses part of the roadway: verify the luminaire's distribution and its permitted aiming range in the manufacturer's installation instructions before assuming a tilt adjustment is allowed.
- If tilt is changed from the documented default: tilt and aiming can change coverage enough that the layout needs to be remodeled, not just visually re-checked, since installation variance of a few degrees is common and additive with intentional tilt.
- If a property boundary, neighboring home, or driveway approach is near the fixture: treat any tilt increase as a trigger to review glare and trespass at that boundary specifically, since a gain in roadway coverage does not offset a new spillover problem next door.
The manufacturer's permitted configuration, not a general fixture category, sets the actual limit. A luminaire rated for one mounting style does not automatically permit a different aiming angle just because it looks similar to another product.
Complete the Pre-Installation and Field-Verification Check
This is the final readiness gate before spending money on poles and fixtures. Work through it in order: unresolved items at the top of the list should be settled before later ones matter.
Before purchase and installation
- Match the exact model and configuration under consideration to its own photometric file and installation instructions, not to a similar-looking product.
- Confirm measured pole locations, mounting height, setback, road geometry, and known obstructions against the modeled layout.
- Identify any local review or permitting step required for the specific project before finalizing the order.
- If a store listing is being used only as a starting reference, such as the Cobra Series LED parking lot light, request the roadway photometric file and installation instructions before specifying it for a spacing plan; a listed lumen output, voltage, or IP rating does not by itself establish coverage on this particular road.
After installation
- Compare the installed pole locations, mounting height, and aiming against the approved modeled layout.
- If a dark band, glare, or trespass issue appears after installation, have it investigated as a field condition against that approved layout rather than adjusting fixtures by trial and error.
- For an existing-pole retrofit, our existing pole layout guide covers how to verify reused poles before this stage.
We do not provide high-voltage wiring, live-testing, or circuit-design instructions in this guide; have a licensed electrician or other qualified professional handle wiring, testing, and any code-compliance decisions for the installation.
FAQs
Does DarkSky approval prove a private-road lighting layout will work?
No. DarkSky's luminaire program checks defined product criteria under its approved luminaire guidelines, such as electrical safety listing, CCT limits, shielding, and upward-tilt constraints. However, it does not test or certify a specific private-road spacing result or confirm local approval. Check the exact current listing for the luminaire under consideration, then still obtain a site-specific photometric plan before finalizing pole spacing.
Is a taller pole always better for eliminating dark bands?
No. A taller pole changes the geometry, which can shift the coverage pattern and change how far light travels, but taller alone does not guarantee better uniformity. Compare the proposed mounting height and spacing together in the actual photometric model for the specific luminaire, since a taller pole with the wrong distribution can still leave a dark band.
What should I look for when selecting a luminaire for a private road?
Lumens and wattage describe total output and power draw, not where the light actually lands on the road. Request the exact IES or LDT photometric file, the distribution type, the manufacturer's mounting and tilt instructions, and a site-specific layout calculation before choosing between candidate luminaires, since two fixtures with similar lumen ratings can produce very different roadway coverage.
