How is a Chimney lit?
Lights set just below the rim, more at equal tiers down the stack, and enough around each level to be seen from every direction.
A chimney is a tall, narrow fixed object, so it is lit like any other obstacle. The light class follows the height: fixed red low-intensity lights on lower stacks, medium-intensity lights on taller ones, and high-intensity white lights on the tallest.
What is different about a chimney is the smoke. Hot gas, soot and fumes leave the rim and would hide or foul a light placed right at the top, so the top lights are set a short distance below the rim. Further lights are then 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, with more lights as the diameter grows.
By day, the chimney is typically marked with alternating bands of orange or red and white, with an odd number of bands so the darker colour sits at both ends.
| Part | Treatment | Notes |
|---|---|---|
| Top level | Lights below the rim | Kept clear of the plume and soot. The distance below the top is set by the regulator |
| Intermediate tiers | Equal spacing | Spaced as equally as practicable between the top lights and the ground, or the tops of surrounding objects |
| Each level | All-round | Enough for an all-round view, typically three to eight by diameter (check the regulator’s table), plus an extra light where one is shielded |
| Shaft | Day bands | Alternating orange and white, odd number of bands, darker at both ends |
| Chimney 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
The height above ground, and above any surrounding tops, decides whether low-, medium- or high-intensity lights are used.
Place the top lights
Set them a short way below the rim so smoke does not hide them or foul the lenses, with enough around the circumference to be seen from any side.
Add the tiers
Space further levels as equally as practicable from the top lights down to the ground, within the maximum gap for the light type.
Mark and monitor
Paint the day bands where required, and monitor each light so a failure is found and reported quickly.
Smoke and heat
Flue gas can cover the lens with soot and attack the fixture, so lights must suit a hot, corrosive setting and sit below the rim.
Hard to reach
Lights sit high on a narrow shaft. Long-life LED fixtures and a way to lower or reach them cut the number of climbs.
Lightning
A tall stack attracts strikes, so the lights, cables and control equipment need surge protection and good earthing.
Failure shows fast
A dead light leaves a dark side or a gap in the tiers. A failure alarm helps, and outages are normally reported to the authority.
Three things on a chimney are easily confused:
- Obstacle Lighting→ the aviation lights that show the chimney to pilots, at night and, for white lights, by day
- Day Marking→ the painted bands that make the chimney visible by day; paint does nothing at night
- Plant and Access Lighting→ lights on platforms and ladders for workers; they do not count as obstacle lights
Also note that a top light set below the rim still serves as the top light: it should be as high as the smoke problem allows, not moved down for convenience.
ICAO Chimney Lighting
ICAO Annex 14 Volume I, Chapter 6, treats a chimney as a fixed object. 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, but for a chimney or similar structure the top lights are placed sufficiently below the top to minimise contamination by smoke. 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 chimney is marked in alternating contrasting bands unless white lights are used by day. Take the light type, number, spacing and marking from the regulator's determination and the current edition of the standard.
FAA Chimney Lighting
The FAA covers chimneys 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). As with ICAO, the guidance asks that the top lights of a chimney be placed so that smoke does not hide them, sets the number of light levels by height, and gives the number of lights around a cylindrical structure by its diameter, such as three at 120 degrees for the smallest and more, at closer angles, for larger diameters. Confirm the current edition of the advisory circular and the style the FAA determination requires for your chimney.
Frequently Asked Questions
Q1How is a chimney lit for aircraft?
With obstacle lights chosen by the height of the chimney: fixed red low-intensity lights on lower stacks, medium-intensity lights on taller ones and high-intensity white lights on the tallest. The top lights sit a short distance below the rim, more lights are added at equal intervals down the stack, and each level has enough lights to be seen from every direction. By day the chimney is usually marked with painted bands.
Q2Why is the top light not right at the top of the chimney?
Smoke, hot gas and soot rise from the rim. A light at the very top would be hidden by the plume and fouled by deposits, so the standard asks for the top lights to be placed sufficiently below the top to minimise contamination. The exact distance below the rim is set by the regulator.
Q3How many lights are needed around a chimney?
Enough that a light at each level is visible from every direction. ICAO sets no fixed count; national guidance gives tables, and a common rule of thumb for round stacks is three lights per level for diameters under about 6 m, four for about 6 to 30 m, six for about 30 to 60 m and eight above that. Where a light is shielded by another object, an extra light is added.
Q4How far apart are the lights up a tall chimney?
Intermediate lights are spaced as equally as practicable between the top lights 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.
Q5Why are chimneys painted in orange and white bands?
The bands make the chimney stand out against the sky by day. The pattern is an odd number of alternating contrasting bands with the darker colour at both ends. Where white lights are used by day, the regulator may allow the marking to be omitted, so check the determination for the stack.
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