High-Mast Light

High-mast lighting mounts multiple high-output floodlights on a single mast of roughly 20–50 metres to cover a large area from very few structures: highway interchanges, ports and container terminals, rail yards, airport aprons, large car parks and stadium surrounds. The trade is deliberate — fewer obstructions on the ground and more uniform coverage, paid for with a taller, more expensive structure and access that needs engineering rather than a ladder.

What Counts as High Mast

There is no universal legal boundary, but practice draws it around 18–20 m. Below that, poles carry one or two heads and the design behaves like conventional street or area lighting. Above it, the mast carries a ring of heads aimed as a group, the structure becomes a genuine civil-engineering item, and maintenance access has to be designed in from the start.

Typical Specification

A complete high-mast specification is a structural document as much as a lighting one. It should state:

1. Mast height, material and finish — usually hot-dip galvanised steel, polygonal or tubular section.
2. Head count, wattage and distribution — symmetric or asymmetric optics selected per position on the ring, not uniformly.
3. Aiming angles from the photometric study, recorded so they can be reproduced after maintenance.
4. The raising and lowering system — winch, ring and cable specification, or a fixed head frame with a defined service arrangement.
5. Electrical detail — feeder sizing, surge protection, and control (photocell, timeclock or dimming profile).
6. Structural deliverables — wind loading class, foundation design, anchor bolt schedule and deflection limits.

Items 1 and 6 normally belong to a structural engineer rather than the lighting supplier, and confusion over who owns them is one of the most common causes of programme delay on high-mast projects.

Design Rules That Actually Govern

Coverage is a radius, not a rectangle. A mast lights a roughly circular pool, and the useful working radius is commonly on the order of 1.5–2× the mast height, falling off toward the edge. Layouts are therefore built from overlapping circles, and the overlap is where uniformity is won or lost.

Aiming is engineered, not eyeballed. Each head on the ring gets its own tilt and rotation from the photometric model. A ring of identically aimed heads produces a bright halo with a dark centre — the classic symptom of a mast commissioned without a study.

Height buys uniformity and costs glare control. Raising the mast flattens the distribution and improves uniformity, but the fixtures become visible from much further away. Cut-off optics and tilt limits are what keep a 40 m mast from becoming a regional light trespass complaint.

Maintenance cost dominates the life cycle. Mast-top service means a crane or a working lowering system. This is why LED conversion changed the category so decisively: heads rated for tens of thousands of hours remove most of the reason to go up at all.

Why LED Replaced HPS on Masts

Four advantages that compound:

• Directional output. HPS heads emitted in all directions and relied on reflectors; LED optics place light on the target, so less wattage produces the same ground illuminance.
• Instant restrike. A HPS head that trips takes 10–15 minutes to return. An LED head returns immediately — decisive for port and apron operations.
• Lumen maintenance. L70 design lives in the tens of thousands of hours cut the number of lowering operations across the asset’s life.
• Controllability. Dimming profiles and zone switching let a yard run at reduced level outside operating hours, which is impossible with discharge sources.

Typical LED head ratings on masts run in the 300–600 W class, replacing kilowatt-class HPS positions, with higher ratings used on the tallest port and stadium-surround masts.

High Mast vs Conventional Pole Lighting

For the full design method — heights, spacing, head counts and a worked layout — see the high mast lighting guide.