Solar Street Light Pole Height and Spacing: A Practical Guide

What the two variables actually control

Mounting height sets how evenly light spreads across the carriageway and how much glare a driver sees. Spacing sets how much the illuminance dips between two poles. If the spacing is too wide for the height, the road develops dark bands at mid-span; if it is too tight, the installation costs more than it needs to for no lighting benefit. Because the pair works together, a specification that names a height but not a spacing cannot be checked.

Height against road width

As a starting point for single-sided lighting, the mounting height is often selected so that the horizontal reach is roughly one to one and a half times the height. On a 7 m carriageway, an 8 m mounting height places the luminaire far enough back to cover the far kerb without pushing light onto the verges. Narrow service roads, footpaths and parking aisles are usually lit from 4 m to 6 m; wider arterials from 10 m to 12 m, often with double arms or twin rows. These are conventions drawn from common practice, not fixed rules, and local road authority standards take precedence where they exist.

Spacing-to-height ratio

Spacing is usually quoted as a ratio. Typical values seen in road lighting design:

Solar schemes often sit at the wider end, because each pole carries its own energy system and halving the pole count halves the number of panels and batteries. The penalty is that light quality, not cost, is what suffers first.

A worked example

Assumptions: a 7 m carriageway, single-sided lighting, 8 m mounting height, 30 m spacing (ratio 3.75 : 1), a target average maintained illuminance of 10 lux with a uniformity ratio of at least 0.4, a utilisation factor of 0.4 for the road-side geometry and a maintenance factor of 0.8.

Lit area per pole = 30 m × 7 m = 210 m². Required average illuminance = 10 lux, so lumens needed on the road = 10 × 210 = 2,100 lm. Divide by the product of utilisation and maintenance factors: 2,100 ÷ (0.4 × 0.8) = 6,563 lm at the luminaire. A modern LED luminaire delivering around 120 lm/W therefore needs roughly 55 W to 60 W of connected power at 6,500 lm output. A 60 W luminaire with a symmetric type-II or type-III distribution is a reasonable candidate, and the supplier’s photometric file should be used to confirm it.

Energy per night then follows from the dimming profile. If the luminaire runs at full output for four hours and 30% for six hours: (60 W × 4 h) + (18 W × 6 h) = 240 + 108 = 348 Wh per pole per night. On an annual-average basis that looks small; on a worst-month basis the panel must be sized to replace 348 Wh on the darkest day of the year, which is where autonomy sizing comes in. Now push the spacing to 60 m: the same 10 lux over 60 m × 7 m requires 4,200 lm on the road, or 13,125 lm at the luminaire, which is a 120 W luminaire and roughly double the nightly energy per pole. Total energy along the road is unchanged, but pole, foundation and installation labour costs halve while glare and mid-span darkening get worse.

The pole is a structure, not a pipe

A solar pole carries a much larger wind area than a mains pole, because the panel sits at the top where the lever arm is longest. Specifying the pole means stating the design gust wind speed, the terrain or exposure category, the panel’s projected area and tilt, and the standard the structural calculation follows. The result is usually expressed as a pole class or a bending moment at the base plate. A common failure mode is to buy a pole sized only for the luminaire and then add a 2 m² panel later.

Also confirm the pole’s material and wall thickness, the taper, the base plate and anchor bolt pattern, and the corrosion protection. Hot-dip galvanizing to a recognised standard should be measured as a coating thickness or mass on the finished item, and the tender should say so. Where a coastal site is involved, add the salt-spray exposure to the specification rather than relying on a standard coating.

Foundations and where the battery lives

Spacing decisions carry straight into the foundation design. Wider spacing means taller poles and larger eccentric loads, so the foundation grows faster than the pole count falls. Decide early where the battery will sit, because it changes the foundation and the cabling:

• In or on the foundation — cooler and reasonably secure, but needs a sealed, lockable compartment with drainage and a route for moisture to escape.
• Pole-mounted box — easier to service and to protect from standing water, but hotter in summer and adds wind area.
• Underground chamber beside the pole — good thermal behaviour and theft resistance, but requires excavation, waterproof glands and a documented drainage path.

Whatever the choice, the decision belongs in the BOQ as its own line, described precisely enough to be inspected. The link between geometry and the equipment list is covered in how to read a solar street light BOQ.

How we can help

We are a China-based trading and project sourcing company, not a manufacturer. We review specifications and BOQs, match a product and configuration to your site conditions, source from qualified manufacturers, and manage quality through to pre-shipment inspection. If you are preparing a tender or specification and want a second opinion, contact us.