The key isn’t the hard part. Getting the light on a face to agree with the light in the virtual scene — that’s where a composite lives or dies.
Ask most people what makes or breaks a green screen shot and they’ll say the key — the quality of the edge, the spill, the fringing. Fair enough; a bad key is obvious. But on our stage at DocShed, the key is rarely the thing that keeps us fiddling. The thing that keeps us fiddling is the light.
Here’s the problem in one sentence: if the light on your talent doesn’t match the light in the virtual world behind them, the brain rejects the shot before it can even name why. The subject looks pasted on. And because we composite in real time — the final image is up on the monitor as we shoot, not discovered weeks later in post — we can see that mismatch immediately, and we can fix it while the camera’s still warm. This is how we go about it.
Light the virtual world first
The mistake is to light the talent and then hope the environment agrees. We do it the other way round. Before anyone stands on the mark, we’ve already built and lit the virtual set in Unreal Engine, so we know exactly where the light is coming from in that world — its direction, its colour, whether it’s a hard midday sun or a soft north-facing window, and whether there’s a motivating source in frame, like a practical lamp or a window.
That virtual lighting becomes our brief for the physical stage. If the scene has a warm key raking in from camera-left at a low angle, then that’s the key we build on the floor — same side, same height, same warmth. If the environment is an overcast exterior, we’re not putting a hard source anywhere near the talent. It sounds obvious written down. On a busy day, with the clock running, it’s the discipline that separates a shot that sits from a shot that floats.
The wrap is what sells it
A key light matched for direction gets you most of the way. The colour wrap gets you the rest.
In the real world, a subject picks up colour from everything around them — the sky, the walls, the grass. On a green screen that ambient bounce is missing, and worse, the only thing bouncing onto your talent is the screen itself, which is exactly the colour you’re trying to remove. So we do two jobs at once: kill the green spill, and replace the missing ambient with the right one.
For that we use LED reference lighting panels positioned to wrap the talent in the environment’s ambient colour — a cool fill for a blue-hour exterior, a warm one for an interior lit by tungsten practicals. Tune those panels to the scene and the subject stops looking like they’re standing in a green room and starts looking like they’re standing in the world. Spill control does the unglamorous half: flagging and distance so the green cyc lights cleanly for the key without throwing green back onto skin and hair. Get the balance wrong in either direction and you’re fighting it in the grade later — which rather defeats the point of working in real time.
Judge it live, not in your head
None of this is guesswork, and that’s the part we’d most want a visiting filmmaker to see. The composited image is on a Rec 709 colour-matched monitor via Assimilate Live FX as we light. So when we nudge the key half a stop or warm the wrap by a couple of hundred kelvin, we’re not imagining what it’ll do to the final shot — we’re watching it happen to the final shot.
That feedback loop changes how you light. You stop lighting the person in isolation and start lighting the composite. Push the rim a touch and you see the subject separate from the virtual background in real time. Cool the shadow side and you watch them settle into an overcast plate. It’s a faster, more honest way to work than lighting blind and praying the elements marry in post — and it’s the whole reason we built the stage around real-time compositing in the first place. We’ve written before about the colour side of this on the vedrí Journal; the light itself is the other half of the same job.
The green screen paradox
There’s a tension baked into all of this that’s worth naming, because it’s the bit that takes experience rather than kit. You need enough light on the green to key cleanly, but every bit of light on the green is a potential source of spill onto your subject. Push the cyc lighting up for a cleaner key and you risk contaminating the very edges you’re trying to protect. Pull it down to protect the edges and the key gets noisy.
The answer is usually distance and separation rather than brute force — getting the talent far enough off the green that the two lighting jobs stop interfering, and treating the subject lighting and the screen lighting as two problems that happen to share a room, not one. On our Blackmagic Pyxis 6K, monitoring the live key while we balance the two is what lets us find that line quickly instead of chasing it.
What’s next
The exciting shift on the horizon is planning more of this before anyone rigs a light at all. Real-time lighting previs is arriving fast — ARRI’s new LUKA plugin for Unreal, announced this fortnight, lets you test fixtures inside the engine with photometrically accurate virtual lights. We’re keen to trial it as a way to work out our physical lighting brief virtually, on the actual environment, before the shoot day. It won’t replace real light on a real face — but it might mean we walk onto the floor already knowing the answer.
If you’d like to see real-time compositing and lighting come together on the stage, book a studio visit — we’ll happily light a subject into a virtual world in front of you and talk through every choice.
This Fortnight in VP
ARRI unveils LUKA, an Unreal Engine plugin for lighting and camera previs — Photometrically accurate ARRI Virtual Fixtures and cameras inside Unreal, with DMX and LiveLink control, free as a three-month trial. Exactly the kind of tool that could let us plan a lighting brief virtually before rigging a single stand.
Unreal Engine 5.8 lands at Unreal Fest Chicago with production-ready MegaLights — Likely the last major UE5 release before UE6. Production-ready MegaLights means thousands of dynamic lights at fixed cost, which makes real-time lit environments hold up far better on the monitor.
Mo-Sys launches StarTracker Sports Studio — A tracked virtual studio with data-driven graphics built in; a reminder that the same StarTracker tracking tech we rely on keeps finding new homes in live broadcast.
Disguise shows new virtual production workflows at InfoComm 2026 — Updates to Mapping Matter and Designer aimed at making complex setups easier to plan — more evidence that “plan it before you build it” is where the industry’s head is at.
Blackmagic releases DaVinci Resolve 21.0 — A major colour and VFX update with new AI-assisted tools; relevant to anyone finishing VP footage where the on-set look needs to carry cleanly into the grade.
