The Lantern Room starts as a question
Build a small original room: a pale floor, one colored wall, a matte object, and eventually a visible emitter. Keep geometry simple enough that a surprising pixel can be traced on paper. The final project is your CPU light-transport renderer, not a downloaded scene or a checklist of materials.
Radiance is power per projected area per solid angle, measured radiometrically in W·m⁻²·sr⁻¹ after integrating over wavelength. A renderer’s linear RGB is a chosen color representation of that directional light; it is not automatically a calibrated physical measurement. A pixel is not a physical light measurement until the camera, exposure, and reconstruction choices are specified. Start by recording the ray and the linear RGB quantity you estimate; a display-ready byte is a later representation.
The supplied companion now connects sampling and sphere queries to a small runnable diffuse renderer: a bounded path loop, a constant environment, surface emission, a sample trace, and an image. You can study one complete ray before extending it. Over sixteen weeks you will build the original room, richer materials, direct-light sampling, and progressive presentation, preserving this small reference as a regression scene.
Sketch the room, label one camera ray and one emitter, then list what your existing renderer actually measures or approximates.