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Truss for Lighting Systems: Sizing a Rig for Your Fixtures

How to Size Truss for Lighting Systems: A Practical B2B Guide

Sizing truss for a lighting rig is one of those tasks that looks simple on a quote sheet and becomes complicated on site. Rental companies and event producers need a repeatable method: add up what is being hung, understand the span, choose a section size that matches the job, and keep every connector in the build compatible.

This guide walks through that process step by step. It focuses on practical decision-making rather than engineering theory, and it applies to the aluminum truss systems manufactured and exported by Benjie Stage, including square, flat and triangle profiles in the BJF series, bolt truss (BJT/BJB models) and Pre Truss (BJM36-A).

Start With the Load: Adding Up Fixture Weights

Every truss sizing decision begins with a load schedule. Before choosing a section, list every fixture that will hang from the truss:

• Moving head profiles and wash lights
• Static LED pars and bar fixtures
• Follow spots and beam fixtures
• Cable, data runs, and power distro attached to the truss
• Clamps, brackets, safety bonds, and any rigging hardware

Add the fixture weights first, then add the accessories. Clamps and safety bonds are individually light, but across a 12-meter lighting position with 30 fixtures, they add up quickly. Cable and distro weight is easy to forget and often sits directly on the truss.

A useful habit is to build the load schedule in a spreadsheet with one row per fixture type, quantity, unit weight, and total. This gives a running total that can be compared against the truss configuration planned for use. It also makes it easy to revise when the lighting designer changes the plot.

One important discipline: distribute the load as evenly as possible along the span, and keep heavy fixtures away from mid-span where deflection is greatest. If a design calls for a heavy cluster in the center, that is a signal to revisit the section size or the support plan.

Span Planning Basics

Span is the distance between support points. It is the single biggest factor in how a truss behaves under load. A longer span increases bending stress and deflection, which is why the same truss section that works comfortably over a short span may not be appropriate over a long one.

When planning spans, consider:

• Support positions. Ground supports, towers, or roof beams determine where the truss can be picked up.
• Number of spans. A 20-meter lighting position supported at both ends behaves very differently from the same length supported at three or four points.
• Cantilevers. Any unsupported overhang beyond the last support point adds load to the structure and should be kept short.
• Deflection tolerance. Lighting positions often need to stay visually level, so allowable deflection matters as much as strength.

As a working rule, shorter spans with more support points give more flexibility in section choice and make load distribution easier. If the venue allows additional pick-up points, use them.

Why Section Size Matters

Section size refers to the cross-section dimensions of the truss chord and overall profile. In Benjie Stage's range, square truss sections run from 100 mm to 760 mm, with standard lengths from 0.5 m to 4 m. Larger sections generally provide greater stiffness and load capacity, while smaller sections are lighter and easier to handle.

Section size affects three things that matter on every job:

1. Load capacity. Larger sections handle more weight over the same span.
2. Deflection. Stiffer sections stay straighter under the same load, which keeps lighting positions level and predictable.
3. Handling and transport. Smaller sections are easier to move and rig in tight venues; larger sections need more crew and truck space.

Material also plays a role. Benjie Stage's BJF truss is produced from En-Aw 6082-T6 aluminum, valued in event structures for its strength-to-weight ratio (the BJT14/BJT24-A bolt models use 6061-T6). The alloy and heat treatment work together with the section geometry to determine performance.

Hanging vs Ground-Supported Rigs

There are two broad ways to support a lighting truss, and each has its own sizing considerations.

Hanging rigs are suspended from roof beams, mother grid, or overhead structure using hoists or chain motors. Here, the truss span is defined by the motor positions, and the load path goes up into the venue structure. The key questions are where the pick-up points are, how many there are, and how evenly the load can be spread between them.

Ground-supported rigs use towers, bases, and sometimes ballast to hold the truss up. In this configuration, the truss spans between towers, and the towers carry the vertical load down to the floor. Ground support gives more control over span and is common in outdoor or non-rigging venues. It also means the tower and base configuration has to match the truss load.

Many productions combine both approaches: a ground-supported front truss and a hung rear truss, for example. Whatever the mix, the sizing method stays the same — load schedule first, then span, then section.

Connector Compatibility Within One Build

Connector compatibility is where otherwise good rigs go wrong. Benjie Stage's truss is available with two connector types:

• Conical connectors using a spigot, pin, and R-clip
• Bolt connectors

Both are established systems, but they do not interchange. Within a single build, every truss piece and every connector should belong to the same system. Mixing conical and bolt truss in one span creates assembly problems and compromises the integrity of the connection.

The same principle applies to section size. A 300 mm square truss does not connect to a 400 mm square truss without a transition piece designed for that purpose, and transitions add complexity. For most rental inventories, standardizing on one connector type and a small number of section sizes keeps builds simple and reduces the chance of a missing part on site.

| Consideration | Conical (spigot + pin + R-clip) | Bolt connector |

|---|---|---|

| Assembly speed | Fast, tool-light | Slower, requires tools |

| Connection method | Spigot inserted, pin and R-clip secured | Bolted end plates |

| Best suited to | Rental and touring builds with frequent assembly | Fixed or semi-permanent installations |

| Compatibility | Must match conical truss throughout the build | Must match bolt truss throughout the build |

If an inventory includes both systems, label and store them separately, and confirm the connector type on every drawing before the truck leaves the warehouse.

Putting the Method Together

A reliable truss sizing workflow looks like this:

1. Build the load schedule, including fixtures, cable, distro, and hardware.
2. Define the span and support positions, and decide between hanging and ground-supported rigs.
3. Choose a section size that suits the load and span, with a margin for deflection.
4. Confirm connector compatibility across every piece in the build.
5. Review the plan before the event, not on site.

For related equipment, Benjie Stage's Aluminum Truss range covers square, flat and triangle profiles, bolt truss and pre truss. Lighting positions are often paired with Portable Stage systems, and event perimeters frequently use Crowd Control Barrier products. If guidance is needed on a specific configuration, the Benjie Stage team can review the load schedule and span details through the Contact page.

Key takeaways

• Always start with a full load schedule: fixtures, clamps, safety bonds, cable, and distro.
• Span between support points drives section size; more supports usually means more flexibility.
• Larger sections give more stiffness and capacity, but weigh more and are harder to handle.
• Hanging and ground-supported rigs use the same sizing logic but different support paths.
• Never mix conical and bolt connectors, or different section sizes, within one build unless a proper transition is used.

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