How are masts and towers lit?
A light on the highest point, more at equal tiers down the structure, and enough at each level to be seen from every side.
Radio masts, broadcast towers and cellular towers are among the commonest obstacles. The light class follows the height: fixed red low-intensity lights on lower structures, medium-intensity lights on taller ones, and high-intensity white lights on the tallest.
A light goes on the highest point, which is often the tip of an antenna. Further lights are added at intermediate tiers, spaced as equally as practicable down to the ground, and each level carries enough lights to be seen from every direction. On a lattice tower the legs can block a light, so lights are normally fitted at the corners.
A guyed mast adds a hazard the lights do not show: the guy wires. They are thin, hard to see and reach far from the base, so they are not lit and may be marked separately. By day the structure is typically marked with alternating bands, with the darker colour at both ends.
| Part | Treatment | Notes |
|---|---|---|
| Top | Light on the highest point | Normally the tip of any antenna or lightning rod, where practicable |
| Intermediate tiers | Equal spacing | Spaced as equally as practicable between the top light and the ground, or the tops of surrounding objects |
| Each level | All-round | Corner lights on lattice towers, and an extra light where one is shielded |
| Guy wires | Not lit | Marked separately where the regulator requires it, such as with markers |
| Shaft | Day bands | Alternating orange and white, odd number of bands, darker at both ends |
| Structure height | Light class | Max. gap between tiers | Notes |
|---|---|---|---|
| Under about 45 m | Fixed red | About 45 m | Low-intensity Type A or B. Often a top level only |
| About 45 m to 150 m | Flashing whiteFlashing redFixed red | About 52 m for red types; about 105 m for Type A | Red types are used with day marking. Type A also works by day |
| Above about 150 m | Flashing white | About 105 m | High-intensity, stepped down at twilight and night. Care needed near an aerodrome |
Find the height
Count the full height, antenna included, above ground and above any surrounding tops. It decides low-, medium- or high-intensity lights.
Light the top
Fit the top light at the highest practicable point so the extent of the structure is shown.
Add the tiers
Space further levels as equally as practicable down to the ground, within the maximum gap for the light type.
Cover and mark
Put enough lights at each level for an all-round view, paint the day bands where required, and mark the guy wires if asked.
Legs shield lights
Lattice legs and bracing block a single light from some angles, so lights go at the corners of each level.
Guy wires
Wires spread the hazard far beyond the base and are not lit, so low-level flying near a guyed mast is the risk.
Remote sites
Many masts are unmanned. Reliable power or a standby supply, and remote alarms for failures, matter more than at a staffed site.
Lightning
A tall mast attracts strikes, so lights, cables and controls need surge protection and good earthing.
Three things on a guyed mast are easily confused:
- Obstacle Lighting→ the aviation lights that show the mast to pilots, at night and, for white lights, by day
- Day Marking→ the painted bands that make the mast visible by day; paint does nothing at night
- Guy-wire Marking→ markers on the wires themselves, separate from the lights, where the regulator requires them
Also note that a lit top does not show how far the guy wires extend. The lights mark the mast, not the area around it.
ICAO Mast and Tower Lighting
ICAO Annex 14 Volume I, Chapter 6, treats masts and towers as fixed objects. The light class follows the height, from fixed red low-intensity lights on lower objects to medium-intensity lights from about 45 m and high-intensity lights above about 150 m. One or more lights are placed as close as practicable to the top, arranged to show at least the points or edges of the top of the object. Where a tall appurtenance such as an antenna sits above the structure, the standard covers placing the light at the highest practicable point. Further lights are placed at intermediate levels, spaced as equally as practicable between the top lights and ground level or the level of nearby tops, and the maximum interval depends on the type of light. Enough lights are used at each level for the object to be seen from every direction, with an extra light where one is shielded by another. By day the structure is marked in alternating contrasting bands unless white lights are used by day. Take the light type, number, spacing and marking, including any marking of guy wires, from the regulator's determination and the current edition of the standard.
FAA Mast and Tower Lighting
The FAA covers antenna structures and towers in AC 70/7460-1, Obstruction Marking and Lighting. The lighting style follows the height of the structure and the FAA determination, using fixtures such as the L-810 (steady red), L-864 (flashing red), L-865 (flashing white, medium intensity) and L-856 (flashing white, high intensity). The advisory circular sets the number of light levels by height and the placement of lights at each level so the structure is visible from any direction. Confirm the current edition of the advisory circular, the style the FAA determination requires for your structure, and what it says about marking guy wires.
Frequently Asked Questions
Q1How is a mast or tower lit for aircraft?
With obstacle lights chosen by its height: fixed red low-intensity lights on lower structures, medium-intensity lights on taller ones and high-intensity white lights on the tallest. A light goes on the highest point, more lights are added at equal intervals down the structure, and each level has enough lights to be seen from every direction. By day the structure is usually marked with painted bands.
Q2Where does the top light go if the mast has an antenna on top?
On the highest practicable point, which is normally the tip of the antenna or lightning rod. Where a tall antenna sits above the main structure and a high-intensity light cannot be fitted at its tip, the standard allows the light at the highest practicable point with a medium-intensity Type A light on the top of the structure. Take the arrangement from the regulator's determination.
Q3Why does a lattice tower need more than one light per level?
The legs and bracing can block a single light from some directions. Lights are normally fitted at the corners of each level, for example three on a triangular tower and four on a square one, so that at least one light is visible from any side. Where a light is shielded by something else, an extra light is added.
Q4Are the guy wires of a mast lit?
No. The lights show where the mast is, but guy wires are thin, hard to see and reach out a long way from the base. Regulators may require the wires to be marked, for example with markers, and pilots are expected to keep clear of the whole guyed area. Check what applies to your mast.
Q5How far apart are the lights up a tall mast?
Intermediate lights are spaced as equally as practicable between the top light and the ground, or the level of surrounding tops. The maximum interval depends on the light type: about 45 m for low-intensity lights, about 52 m for medium-intensity red lights, and about 105 m for medium-intensity Type A and high-intensity lights.
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