Low Intensity Obstruction Light

A Low Intensity Obstruction Light is a steady‑burning red aviation warning light installed on structures that are less than 45 metres (150 feet) in height, or as an intermediate light on taller structures. It provides a continuous red visual warning to pilots during nighttime operations, indicating the presence of an obstacle that could pose a collision hazard.

These lights are the most widely used type of obstruction lighting, found on communication towers, wind turbines, chimneys, buildings, and other vertical structures. They are characterised by their low power consumption, long service life (particularly in LED variants), and simple, reliable operation. Low intensity lights are typically rated at 32 candela minimum intensity, making them visible at distances of several kilometres in clear conditions.

Low intensity lighting exists to give shorter structures — those under 45 metres — a simple, minimum-cost warning proportionate to the actual level of hazard they present, rather than requiring every vertical structure regardless of height to carry the same lighting infrastructure as a major tower. A steady-burning signal, rather than a flashing one, is sufficient at this height because the hazard a short structure presents is comparatively localized and doesn't require the extra conspicuity a flashing pattern provides for taller, more distant obstacles. Its purpose is also served by simplicity and low power draw: because this is by far the most numerous category of obstruction light, deployed across huge numbers of towers, chimneys, and buildings, a design that is inexpensive, reliable, and low-maintenance is what makes obstruction marking practical at this scale in the first place.

Low intensity obstruction lights are installed on a wide range of structures:

• Communication towers – mobile phone masts, radio/TV broadcast towers.
• Wind turbines – as intermediate or top lights.
• Chimneys and smokestacks – industrial and power plant structures.
• Buildings – high‑rise structures that exceed height thresholds.
• Transmission towers – electrical power line pylons.
• Masts and poles – meteorological, navigational, and utility masts.
• As intermediate lights on tall structures – in combination with medium or high intensity lights.

Fixtures are mounted at the top of the structure and, where used as an intermediate light on a taller structure, at the levels specified by the applicable lighting scheme, typically on a simple bracket suited to the structure type — a pole-top mount on masts and poles, a facade bracket on buildings, or a lattice-arm mount on towers. Given the low power draw and light weight of these fixtures, mounting hardware is comparatively simple, though it still needs to hold the light clear of the structure's own members so it isn't shadowed from any direction. Cabling is run along the structure back to a photocell or timer, often self-contained within the fixture itself in modern LED variants, which simplifies installation on structures that lack an existing power and control infrastructure. Because this is the most numerous category of obstruction light, installations are frequently standardized across large numbers of similar structures (towers, poles, short buildings) using the same bracket and wiring arrangement at each site.

Low intensity obstruction lights operate on a simple but essential principle:

• Light Source: Traditionally using a low‑wattage incandescent or halogen lamp (typically 10–25W), modern systems increasingly use high‑brightness LEDs for improved energy efficiency and longer life.
• Colour: The light emits a steady red beam, which is the internationally recognised colour for obstruction warning. Red is chosen for its high visibility against the night sky and its minimal impact on night vision.
• Beam Pattern: Most low intensity obstruction lights are omnidirectional, emitting light uniformly in all horizontal directions (360°) to ensure visibility from any approach angle.
• Operation: The light operates automatically, typically controlled by a photoelectric sensor (day/night switch) that turns the light on at dusk and off at dawn. Some systems are controlled remotely via a central monitoring system.
• Power: Low intensity lights are typically powered from the local mains supply (110/230V AC) or via a dedicated solar‑powered system for remote locations.

Low intensity obstruction lights carry the simplest control architecture on the airfield: there is no shared circuit or central controller involved in day-to-day operation. Each fixture is powered directly from local mains or a dedicated solar-battery system, and a photoelectric day/night sensor built into (or wired directly to) the fixture is the entire control loop — it switches the lamp on at dusk and off at dawn with no other input required. Where a taller structure layers a low intensity light in among medium or high intensity fixtures above (as shown opposite), each level still runs its own independent photocell cycle rather than being synchronised to the others, because a steady always-on-at-night signal doesn't need coordination the way flashing tiers do. Some installations wire the light into a central or remote monitoring system so a lamp failure is reported to maintenance staff without a site visit, but that link is purely for status reporting — remove it and the fixture keeps switching on its local photocell exactly as before.

The fixture is a compact, weatherproof unit housed in a moulded polymer or die-cast metal enclosure, sized for straightforward surface- or pole-mounting on shorter structures, guy wires, or building edges where a steady-burning low-intensity marker is sufficient. A red lens covers the LED array or low-wattage incandescent/halogen lamp, gasket-sealed to achieve an IP65/IP67 rating that keeps out dust and driven rain despite the fixture's often unsheltered mounting position. The housing integrates a simple mounting bracket or threaded base allowing quick attachment and orientation for omnidirectional beam coverage, with a compact internal compartment for any driver electronics and a sealed cable gland for the incoming power connection, whether mains AC, low-voltage DC, or an integrated solar-and-battery supply. Given the light's typically lower mounting height and easier access, the housing favours simplicity and low maintenance over the heavier sealing and structural bracing used on high-intensity fixtures, while still using corrosion-resistant fasteners and UV-stable materials for long outdoor service life.