Lighting a rock show: reading the rider, building the plot

A touring act travels with two riders bundled together, and only one of them belongs to a production company. A hospitality rider names catering, parking and dressing rooms. A technical rider names the show, and lighting’s share of it is written as a parts list: fixture types and quantities, the console the tour is bringing or expects to find, DMX line routing and snake length, the total amperage the package draws, the length of feeder cable being carried, and the dimensions of anything that hangs — a backdrop’s width and height most often, because a venue has to know it will clear the house before it agrees to fly it.

It is a specification the tour has already tested on other rooms, and reading it early turns a load-in into a checklist rather than a negotiation. What it does not settle is what the venue’s own rig already covers and what has to travel in on the truck to fill the gap — the two questions §02 works through.

A house lighting rig runs from a conventional wash of thirty to ninety PAR cans — close to standard equipment in a working music venue — up to a room carrying several hundred addresses across three universes and a mix of conventional and moving fixtures. Front light is the least predictable part of it: one room hangs ellipsoidals, the next hangs PAR cans, LED pars, moving spots or moving washes, and a rider written against one of those is not automatically satisfied by another.

Trim height is the other variable a rider cannot assume. Venues run anywhere from nine feet of clear height to thirty, and a touring designer’s floor package is built to survive both ends of that range rather than to expect one of them — the standing guidance is to keep a floor truss to about ten feet, an eight-foot truss with a fixture on top of it, so the package still reads under a low room without needing to be rebuilt for a high one. Stage width runs from twenty feet to fifty across the same set of rooms, which is the number that decides how many of anything are needed across the front, worked through in §03.

Reconciling the two documents — what the rider calls for and what the room already has — happens once, on paper, before a single fixture is hung. Doing it after focus has started is the load-in that runs long.

A fixture with a fixed beam throws a cone whose diameter at any distance is twice the throw multiplied by the tangent of half the beam angle — the same trigonometry the event lighting page uses to set the angle a key light strikes a face at, run the other way to solve for spread instead of angle. A fixed-beam fixture is specified by which lens it is fitted with rather than by a zoom setting, and the widely used ETC Source Four ellipsoidal ships with a published menu of them — 5, 10, 14, 19, 26, 36, 50, 70 and 90 degrees — used here to show how the math moves with the lens, not to describe what is on any particular truss.

Take a front truss position twenty-five feet from the stage — an illustrative distance, not a fixed one, since §02 puts real stages anywhere from twenty to fifty feet wide and a truss is hung to suit. A 26-degree lens throws a cone about eleven and a half feet across at that distance: twice 25 feet, times the tangent of 13 degrees. A 50-degree lens from the same trim throws about twenty-three feet across: twice 25 feet, times the tangent of 25 degrees — roughly double the coverage from the same position, with nothing moved but the lens.

Divide those coverage widths into the stage-width range from §02 and the fixture count swings hard. A twenty-foot stage takes two of the narrow lens or one of the wide one to span it; a fifty-foot stage takes five of the narrow lens or three of the wide one. A designer overlaps adjoining beams rather than butting them edge to edge, which pushes every one of those counts up by a fixture or two — but the swing itself is the fact worth keeping: doubling the beam angle roughly halves how many fixtures a front truss needs to cover the same room.

The PAR64 — a par can eight inches across, taking a 500 or a 1,000-watt lamp — is still the fixture most riders size a dimmer rack against. A 120-volt, 20-amp circuit carries 2,400 watts on its nameplate; the same 80 percent continuous-load derate the LED wall page works from leaves 1,920 watts usable. Divide that by a 1,000-watt lamp and the answer is 1.92 — one PAR64 per circuit at full output, not two. Divide it by a 500-watt lamp instead and the answer is 3.84 — three fixtures per circuit, not four. The concentrated figure is always the smaller of the two, the same as it is for a point load on the staging page, and a plot sized off the larger number is a plot that trips a breaker on the first cue.

Apply that to §03’s own numbers: five narrow-lens fixtures across a fifty-foot stage, run as 1,000-watt PAR64s, need three circuits rather than two — 5 divided by 1.92 rounds up, and rounding down is how a rack ends up one circuit short on the day.

A DMX line runs into a limit of its own, and there are two of them rather than one. The addressing budget — 512 channels to a universe, and what that does to a rig full of multi-parameter moving lights — is worked through on the event lighting page. The other limit sits underneath the addressing one and has nothing to do with how many channels are free: the same standard runs DMX over an RS-485 electrical bus, and a single run is rated for no more than thirty-two unit loads before it needs an opto-splitter. A rig can be nowhere near its channel budget and still need a second run, because the limit that stopped it was electrical rather than addressable.

A headline act’s rider is what the room gets built around — the fixture list, the trim heights and the DMX runs in §01 through §04 are drawn to it, and the house or touring rig is patched to match. A support act plays under the same iron on the same night, and the working assumption in touring is the blunt one: a support act is not entitled to any of it. The usual path is asking the tour in advance what portion of the rig will be made available, and having a lighting operator ready to run a show patched and cloned from the headliner’s own desk rather than programmed from scratch, especially where the support act has not brought a console of its own.

Time follows the same hierarchy. A support act’s line check often happens after doors have opened, run on headphones and in-ears while the audience is already filing in, rather than in a quiet room beforehand — and even that much time is never guaranteed. The practical response on the support side is to plan for none of it: travel self-contained, and build a show that does not depend on borrowing anything from the headliner’s crew at any point in the evening.

A support slot still gets full design attention. It is sized to what the truss actually offers that night, not to the rider that was written for the other band.

What a rider itemizes and what a house rig actually carries are two different documents, and the plot is what happens where they disagree. Beam angle and throw distance set the fixture count, the circuit and the DMX line each carry their own separate limit, and none of it is decided by which act is topping the bill — only how much of the result each one gets to call its own.