Chimney Obstruction Light

A Chimney Obstruction Light is a medium‑intensity aviation warning light installed on industrial chimneys, smokestacks, and similar tall structures to alert aircraft of their presence. These lights are typically red (steady‑burning or flashing) and are mounted at the top and sometimes at intermediate levels on chimneys exceeding 45 metres (150 feet). They are engineered to operate reliably in extreme conditions—high temperatures, corrosive flue gases, heavy soot, and severe weather—while maintaining the required photometric output and colour. Chimney obstruction lights are critical for aviation safety near industrial areas, power plants, and incinerators.

Chimney obstruction lighting exists to mark a category of tall structure that combines the usual height hazard with an unusually hostile operating environment for the fixture itself: sustained heat, corrosive flue gases, and heavy soot accumulation that would degrade a standard obstruction light's housing, lens, and photometric output over time if it weren't specifically engineered for this exposure. Because industrial chimneys are frequently sited at power plants and incinerators, often clustered with other tall industrial structures, marking them clearly and reliably matters for the same reason as any tall obstacle — but the light's ability to keep functioning through the specific conditions a chimney generates is itself part of the purpose, since a light that degrades quickly in this environment would fail exactly the structures it's most needed on.

Installed on chimneys, smokestacks, and industrial stacks that exceed 45 metres (150 feet) AGL, or any chimney that falls within an aviation corridor or near an aerodrome. Typically used in power plants (thermal, nuclear, biomass), incinerators, cement plants, steel mills, and chemical factories. Multiple lights are often installed at different levels (top, mid‑height) on very tall chimneys to indicate the overall height and shape. The lights must be visible from all directions, requiring omnidirectional or 360° coverage.

Fixtures are installed at the chimney top and, on taller stacks, at intermediate levels at the specified vertical spacing, mounted on brackets designed to hold the light clear of the flue gas stream and any soot or condensate runoff that would otherwise coat the lens. Mounting hardware and cabling are specified in corrosion-resistant and high-temperature-rated materials given the combination of flue gas chemistry, heat radiating from the stack, and prolonged outdoor exposure. Access for lamp changes and cleaning is typically provided via a permanent ladder, davit arm, or lifting platform built into the chimney design, since the top of an operating stack is not otherwise reachable. Power and control cabling is run down the outside of the stack in a protected conduit to the base, where it connects back to the controller and, on industrial sites, into the plant's own monitoring and alarm systems.

Each chimney obstruction light is powered from a dedicated power supply—either a direct 230V AC line or a low‑voltage system with a transformer. The light typically uses an LED array or a high‑intensity xenon or halogen lamp, with a red filter or dichroic coating to produce aviation red. The intensity is either fixed (medium intensity, ~2,000 cd) or adjustable using a photocell to switch between day and night modes (though many chimney lights are steady red 24/7). A flashing option (20–40 fpm) may be used for enhanced visibility. The housing is constructed from corrosion‑resistant materials (stainless steel, marine‑grade aluminium) with IP66/IP67 protection and high‑temperature seals to withstand stack heat and chemical attack.

Chimney obstruction lights are usually the simplest control chain in the AGL family, and many installations deliberately simplify it further: rather than a photocell deciding day/night mode, the top light is wired permanently on, steady red, 24/7, so there is one less component that can fail silently on an unmanned stack. Where a photocell or timer is fitted, it switches a dedicated power supply — either direct 230V AC or a transformer-derived low-voltage feed, kept electrically separate from the stack's own process and combustion-control wiring — which drives the mandatory top light and any intermediate-level lights required on taller stacks. There is no loop-level dimming or intensity stepping here; each fixture is either fully on or off, with a flashing option (20–40 fpm) available where required by the governing standard. Because chimneys are frequently unstaffed, lamp-failure status is typically wired back to the plant control room or a dedicated remote monitoring unit rather than relying on a site visit, so an outage on an unmanned stack still reaches someone who can act on it.

The fixture is built into a rugged, heat- and corrosion-resistant housing, typically die-cast aluminium or stainless steel, engineered to withstand the elevated temperatures, exhaust gases, and thermal cycling encountered at chimney-top and intermediate mounting positions. A toughened red lens, heat-shielded and gasket-sealed with a high-temperature silicone seal, protects the LED array or halogen/xenon source while achieving an IP66/IP67, corrosion-resistant rating. Mounting brackets are designed to clamp securely to the chimney's curved or tapered structure, often with a standoff to keep the fixture body clear of the hottest exhaust plume while maintaining unobstructed omnidirectional beam coverage. Internal wiring runs through heat-resistant, sealed conduit to a junction box positioned away from direct exhaust exposure, connecting to the 230V AC or 24V DC supply via a weatherproof converter where required. Corrosion-resistant fasteners and coatings are used throughout to withstand the combination of heat, moisture, and chemical exposure typical of chimney environments.