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How it works

LUX Live replaces a per-room Radiance daylight simulation with a single forward pass of a neural network. The prediction takes a fraction of a second per window and runs on an ordinary laptop.

The model​

The predictor is a modified SegFormer semantic-segmentation network (MiT-B4 encoder, feature dimensions 64 / 128 / 320 / 512, a lightweight all-MLP "GLP" decoder). It outputs a 384 × 384 image whose pixel values are the daylight factor at that point on the floor grid, passed through a sigmoid so the output is bounded to the physically meaningful 0–9.9 % DF range. The network is trained with an L1 (mean-absolute-error) loss against Radiance ground truth.

Per-window superposition​

Daylight from different windows adds linearly, so LUX predicts each window independently and sums the per-window DF fields in post-processing. This keeps the model small and lets it handle rooms with any number of windows without ever having seen that exact arrangement in training.

Inputs​

Each window is encoded as a stack of image channels describing:

  • the room geometry (plan outline, ceiling height, floor height above terrain);
  • the window geometry (position, sill and head height, frame ratio);
  • the external obstruction — two angle profiles (horizon and zenith) sampled in 64 directions across a 145° field of view. See Obstruction encoding.

Material reflectances are fixed to the default set in the validated model — see Reflectance and Parameters for the full list.

Training data​

The model was trained on 20,687 rooms generated parametrically in Grasshopper and simulated with Radiance via Ladybug Tools (ab 6, ad 4096, as 4096), on a 0.25 m analysis grid at 0.8 m height, under the CIE standard overcast sky. The rooms span row houses, perimeter blocks, semi-open blocks, slab blocks and tower blocks, with realistic urban obstruction.

From prediction to compliance​

The summed DF field is compared against the selected regulation's threshold and evaluation rule (for example BFS 2024:8: share of habitable-room area at DF ≥ 1.0 %), and each room or dwelling is flagged pass / fail. See Regulations.