Radiosity Lighting Studio | mysimulator.uk

Room & Window

Window position along wall 50%

Daylight intensity 100%

Wall / surface reflectance 55%

Room proportions (depth:width) 1.00

Illuminance (floor)

Average

— lx

Maximum

— lx

Minimum

— lx

Uniformity min/avg

—

How it works

The room's perimeter is discretized into flat wall patches. Each patch i has a reflectance ρ_i and, if it lies inside the window, an emitted radiosity E_i (the daylight source). The steady-state radiosity equation is solved by Gauss–Seidel iteration:

B_i = E_i + ρ_i · Σ_j F_i→j · B_j

2D patch-to-patch form factor:
F_i→j = max(0,cosθ_i)·max(0,cosθ_j) / (2r) · L_j

where r is the distance between patch centers, θ_i/θ_j are the angles between each patch's inward normal and the line joining them, and L_j is patch j's length — the 2D (per-unit-depth) analogue of the classic hemicube radiosity kernel. Wall colour in the scene encodes each patch's converged radiosity B_i.

Floor illuminance is then sampled on a grid: each floor point collects direct + inter-reflected light from every wall patch using the same cosine/distance falloff, producing the heat-mapped floor. Uniformity (min/avg) is the standard architectural lighting metric — IES guidance typically asks for ≥0.4 in a work area; low reflectance or an off-centre window pushes it down by concentrating light near the window wall.

Window position — slides the daylight opening along the north wall.
Daylight intensity — scales the window's emitted radiosity E.
Reflectance — how much light every non-window surface bounces back (ρ), driving inter-reflection.
Room proportions — reshapes the room from a wide shallow space to a narrow deep one, changing how far light reaches from the window wall.

Low illuminance High illuminance

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