Luminaire Geometry Reference
How the five mounting variables interact
Road lighting performance is governed less by any single parameter than by the ratios between them. SINOCO’s calculator treats mounting geometry as a coupled system — change one variable and the tool re-derives the others’ effective contribution rather than treating each in isolation.
| Lane | Avg (lx) | Min (lx) | Max (lx) | Uniformity U0 | Status |
|---|
| Lane | Avg (cd/m²) | Min (cd/m²) | Max (cd/m²) | Uniformity |
|---|
| Class | Lav ≥ (cd/m²) | U0 ≥ | Ul ≥ | TI% ≤ | Status |
|---|
| Class | Eavg ≥ (lx) | Emin ≥ (lx) | Status |
|---|
| Model | Power | Lumens (init) | Efficacy | Voltage | IP / IK | Warranty |
|---|
Setback (S) — the perpendicular distance from pole base to the nearest carriageway edge. Held at 0.3–0.6 m in most municipal specs, but this is a clearance constraint, not a photometric one: it protects the pole from vehicle strikes and keeps maintenance access clear. Push setback too far past 0.6 m on a narrow road and you start cutting into the optic’s useful throw before light ever reaches the far lane.
Arm length (A) — horizontal reach from pole shaft to luminaire center. Single-arm configurations run 1.5–2.5 m; this is the dimension that determines how far over the carriageway the light source actually sits, which directly sets how symmetric the Type III/Type IV beam pattern lands across the lane width. Double-arm (twin) brackets exist specifically to light both directions of a divided carriageway from one pole line — useful where land take or trenching cost rules out a staggered single-arm layout.
Overhang (O) — horizontal distance from luminaire center to the road edge, not to the pole. The governing constraint is O ≤ H/4 (H = mounting height). Exceed that ratio and the luminaire’s high-angle output starts spilling past the intended cutoff line — the practical symptoms are glare complaints from oncoming traffic and light trespass onto adjacent property, both of which show up as TI% (threshold increment) failures in compliance simulation before anyone files a complaint.
Arm inclination (θ) — angle between the optic’s emitting plane and horizontal, capped at 15° industry-wide. In current practice θ = 0° dominates new installations, because tilting the optic upward to throw light farther down-road also lifts the upward light ratio (ULR) and high-angle intensity — the two metrics most LED retrofits are specifically trying to suppress versus legacy HPS/HID. Tilt is a tool for extending throw on wide carriageways with tall mounting heights, not a default setting.
Pole spacing (P) — center-to-center distance along the road axis. The working range is P = 3.0–4.5 × H. This ratio exists because uniformity (U0) collapses geometrically as spacing grows relative to height — wider spacing trades a lower pole count (capital cost) against deeper troughs in illuminance between poles (uniformity risk). SINOCO’s heatmap renders this tradeoff directly: drag spacing past ~4× height on a fixed mounting height and watch the dark band between poles widen before the U0 readout drops below class threshold.
Design Workflow: From Road Survey to Compliance Sign-off
A compliant street lighting design isn’t selected — it’s converged on through iteration against a target class. The process below mirrors what SINOCO’s calculator automates internally; the same sequence applies whether you’re using simulation software or working the numbers by hand.
1. Classify the road. Pull lane width, carriageway width, surface type (R-class: R2 semi-diffuse asphalt / R3 diffuse wet asphalt / R4 mostly-diffuse concrete), traffic volume, and pedestrian activity. These inputs determine which lighting class you’re designing toward — ME-series (motorized traffic, EN 13201) or the equivalent RP-8-21 class in North American practice. Get the classification wrong upstream and every downstream calculation targets the wrong bar.
2. Select the fixture and load its photometric file. Choose wattage, lumen package, and optical distribution (lens type) based on the target class, then bring in the manufacturer’s IES/LDT photometric file — this is the measured candela distribution that simulation software (or a calculator like this one) uses to project illuminance onto the road surface. Skipping this step and eyeballing wattage against road width is how undersized or oversized installs happen.
3. Fix the mounting geometry. Decide arrangement — single-side, staggered, opposite, or center-median — then lock in height, arm length, overhang, tilt, and spacing using the ratios above as bounds, not targets. This step and the previous one are not independent: a wider optic (Type IV/V) tolerates wider spacing at the same height; a narrow Type II/III does not.
4. Run the simulation. Compute Eavg, Emin, U0, luminance Lav, and uniformity Ul/U0 across the full road cross-section, lane by lane. This is the step where geometry assumptions get tested against actual numbers instead of rules of thumb.
5. Check against class thresholds — and iterate if it fails. Compare results against the EN 13201 ME/CE table or RP-8-21 equivalents. A failure here isn’t a dead end — it’s a pointer to which variable to adjust: low U0 usually means spacing is too aggressive for the mounting height; low Eavg with good uniformity usually means underpowered fixture, not bad geometry. Adjust and re-run rather than discarding the layout.
6. Lock the design and document it. Once every required metric clears its threshold, the configuration becomes the basis for the final simulation report — the artifact that gets handed to whoever signs off on the installation.
SINOCO’s calculator collapses steps 3 through 5 into a live feedback loop: every slider move re-runs the simulation and re-checks compliance in real time, so you can see which boundary you’re approaching before you commit to a pole order.
Reading the Numbers
A calculator is only as useful as the engineer’s ability to act on its output. A few notes on interpretation:
- U0 below class threshold with otherwise healthy Eavg points to spacing or overhang, not fixture selection. Tightening spacing or widening the optic’s distribution typically resolves it without changing wattage.
- Eavg below threshold with healthy U0 points to fixture output, not geometry — step up wattage/lumen package or reconsider maintenance factor assumptions before touching pole layout.
- TI% near its ceiling is an early-warning sign for overhang or tilt creeping past their structural limits, even if every other metric currently passes. Address it before it becomes a glare complaint in the field.
Disclaimer
Outputs from this calculator are engineering estimates intended to support preliminary design and product selection — they are not a substitute for certified photometric simulation (DIALux, Relux, AGi32, or equivalent) and should not be submitted as-is for tendering, procurement, permitting, or construction sign-off. Final designs must be verified by a qualified lighting professional against actual site survey data, the applicable regional standard (EN 13201, RP-8-21, or local equivalent), and manufacturer-issued photometric files for the specific fixture being installed. SINOCO accepts no liability for outcomes based on unverified calculator output.