ACL

Overview

ACL stands for Aircraft Landing Light. It is not a classic film spotlight model, but a sealed PAR lamp (Sealed-Beam with integrated parabolic reflector) originally developed for aviation, which is repurposed in stage, concert, and film lighting.

The defining characteristic of the ACL is its extremely narrow, nearly parallel beam of light. Unlike a normal PAR spot, which scatters slightly, the reflector bundles the light into an almost collimated beam. This keeps the beam narrow and sharply defined over long distances – ideal for visible "beam" effects, for example, when the light beam is passed through fog/haze.

Technical Fundamentals

ACL lamps are constructed as sealed Sealed-Beam units and are common in the typical PAR sizes of PAR36 and PAR64. They operate on a low voltage of 28 V (DC in aviation) – this voltage comes from the onboard electrical system of aircraft.

A common type is the GE 4552 (PAR64, 28 V, 250 W). In addition, ACL lamps of other PAR sizes and higher wattages exist.

Use on Set and Stage

Because ACL lamps can only handle 28 V, they cannot be directly connected to the usual mains voltage. In practice, therefore, four ACL lamps are typically connected in series (4 × 28 V ≈ 112 V), so they can be operated approximately on 120 V mains. For this purpose, there are pre-assembled ACL bars – strips with four hardwired PAR64 ACL units.

ACLs are primarily used where hard, directed beams are to be made visible – as beam effects in concert and music video looks, as well as for sharply defined cones of light. For the film look, they provide a hard, directed light with low scatter.

LED Successors

Today, the term "ACL" is also used for modern LED effect lights that replicate the characteristic narrow ACL beam (sometimes with very narrow beam angles). These operate directly on mains voltage or with their own power supply and replace the old 28 V series connections, but retain the optical beam look.