A Thrust With No Front Light
A lighting designer is plotting a naturalistic two-act play on a 3/4 thrust with seating on three sides and no front-of-house catwalk. The only frontal positions are two box-boom bays at the upstage corners of the side seating, roughly 55 degrees off center. The rep plot provides 20 ellipsoidals, 12 fresnels, and 6 PAR cans across 18 dimmer circuits, each rated 20 amps at 120 volts. Gel stock is limited to a few sheets each of a warm amber, a pale straw, a saturated blue, a lavender, and a green, plus frost. The director wants a realistic living room with a visible window for a sunset, a practical table lamp an actor switches on, and a moonlit exterior beyond the window. The inventory is entirely 575-watt fixtures. The designer also wants a strong saturated blue for the moonlight.
1. Explain how you would allocate positions and circuits on a stage with no frontal light, and what you would tell the director about what is achievable.
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Build from azimuths, not from a wash.
Two box booms 55 degrees off center are modeling positions, not face-lighting positions. From those bays the downstage third of the thrust is nearly unlit while the upstage third is over-lit - the opposite of where actors need help.
- Upstage two-thirds: the booms become the primary front. Hang high and use narrow barrels, since throw distance is long.
- Downstage tip: add two ellipsoidals at the downstage ends of the side seating, or on a temporary position cleared with the house manager before the plot is final. Without them the apron is a hole.
- Top and back: fresnels as a top wash on the thrust, PARs as backlight from four corners. On a thrust, top light is what gives a face a readable plane for spectators sitting at 90 and 180 degrees.
- Specials: a hard-edged special for each of the three playing areas, plus the window and the lamp, so the director can isolate without a full wash.
Tell the director plainly: keep elevations near 45 degrees. Lower flattens; higher puts eyes in shadow and throws deck shadows into the side seating's sightline. On a thrust there is no angle that flatters everyone at once - the design is a set of compromises, stated out loud.
2. How do you realize the window, the sunset, and the practical lamp physically on a thrust, where a fourth wall cannot exist?
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Solve the story, not the architecture.
No audience on three sides will ever see "through" a window in a box set: it faces one third of the house and presents its back to the other two.
Environmental suggestion. Build the window as a frame with a translucent or scrim panel, and place the sunset source upstage of it, low and raked. The audience sees the glow and, crucially, the frame's shadow thrown downstage across the floor. A long warm shaft raking across the deck reads as late sun from every seat, because light behavior, not carpentry, is doing the storytelling.
Or abandon the fourth wall honestly. Stand the window as a fragment in the upstage wall with the room's downstage edge open. Audiences accept a fragment when the light behaves like a window.
Practical lamp. Give it its own circuit - a practical cannot share with a wash or you cannot fade it independently. Use a real switch the actor can hit reliably and test it twenty times. Blend the lamp's small warm pool into the room with a soft fresnel at low intensity; that pool, not the window, is usually what sells the interior at the top of the act.
3. Check the electrical allocation and resolve the designer's request for a saturated blue moonlight. Show the reasoning.
Read the worked answer
Do the arithmetic first; the color question is second.
Each circuit is 20 A at 120 V, so 2,400 W theoretical. Standard practice is to load to about 80 percent - roughly 1,900 W - leaving headroom for inrush and heat. Four 575-watt units draw 2,300 W: legal on paper, over the derated limit, and a trap on a rep plot where someone later adds a fifth fixture. Three per circuit (1,725 W) is safe. Eighteen circuits at three units each is 54 slots, but the inventory is 38 fixtures, so hang a plot of roughly 30 units and reserve circuits for the practical and the specials. Never two-fer into a circuit without re-adding the load.
Color. A saturated blue gel drops the value of a 575-watt unit so far that a face at 55 degrees off center reads darker than the shadow around it - moonlight becomes a hole in the stage picture. Correct it three ways: go to a less saturated blue and let a drop in intensity carry the effect; add frost to soften the beam edge; keep the warm side at low level rather than at zero, so the face retains a plane. Reserve the truly saturated blue for the window exterior and the backlight, where silhouette is the entire point.