A high mast lighting system consists of three main sub-assemblies: mast structure, headframe, and luminaires. The headframe can be further divided into the fixed and mobile types. In a system with a mobile headframe, the mast structure has a winch mechanism which allows the headframe to be lowered to ground level for luminaire maintenance. The mobile headframe comes with a latching mechanism that holds the entire weight of the headframe and luminaires. In fixed headframe systems, the mast either has rungs/ladders or a motorized lift system via which the maintenance platform can be accessed. The mobile access system can be a mobile step system gliding on two rails fixed to the mast, or a power lift consisting of a cage, a guidance system, an elevator winch system and a safety braking system.
The headframe where a cluster of luminaires are mounted comes in variety of forms. The fixed equipment includes crossarms, rings, and frames. Crossarms such as U-bolted straight crossarms and curved crossarms are designed for lightweight lighting assemblies that use a limited number of luminaires. Rings and frames host more luminaires. A maintenance platform is usually fixed in close proximity to the crossarms, rings or frames to enable convenient servicing. The platform may also be structurally integrated with rings or frames to serve as a headframe assembly. A tilted frame with a central shaft is designed to accommodate a huge number of luminaires for single-side floodlighting. This type of headframes is most often found in stadiums where an exceptional uniformity of illuminance is critical. The mobile headframe is typically a ring structure which is suspended by stainless steel cables passing downwardly from pulleys on top of the mast to a winch in the base of the mast.
The masts are made of high tensile steel plates confirming to BS EN 10025 or equivalent standards and are hot dip galvanized after fabrication. They are continuously tapered and come in a round-conical or polygonal cross section. The mast is delivered to site in sections which fit into one another to achieve a desired height. Masts may come with a hinge which allows to bring the headframe down to human heights for ease of maintenance. The hinged mast has a fixed mast base and an upper part hingeable at either mid-level or the bottom. A weather and vandal resistant door is provided in the base of the mast to provide access to the base compartment equipment like winch, motor, cable. A flange plate, which is welded to the base of the mast, allows the mast to be secured to the foundation by anchor bolts bonded in the foundation block.
