Radiance — The Complete Guide: Free, Physically Accurate Daylight and Lighting Simulation
Radiance is a ray-tracing lighting simulation engine developed at Lawrence Berkeley National Laboratory (LBNL). It computes natural and electric light in a building in physical values — lux and luminance — not just a pretty picture. It is the engine behind most daylight calculations in green building standards worldwide, and accurate enough to serve as evidence in design.
Radiance
Lawrence Berkeley National Laboratory
Physically accurate daylight and lighting simulation — the basis for green building light calculations.
Get it from the vendorWhat you get
- Illuminance — lux on a work plane over a grid of points, for example the daylight factor.
- Annual metrics — daylight calculations over a whole year from a weather file.
- Glare — glare assessment from the occupant’s point of view.
- Physical images — renderings with real luminance values in every pixel.
- Shading systems — blinds, special glazing and light shelves.
How to use it
Radiance itself is a collection of command-line tools that work with a text scene description. Most engineers and architects use it through another interface: Ladybug Tools in Grasshopper, OpenStudio, or commercial programs built on it. Learn the parameters for the number of bounces and accuracy — they decide result quality and run time.
Related tools
For whole-building energy simulation — EnergyPlus. For optical properties of glazing — WINDOW. For quick visual renderings — Blender.
EnergyPlus
US Department of Energy
Annual building energy simulation — envelope, HVAC, thermal comfort and daylight. The US DOE engine.
Get it from the vendorOpenStudio
National Renewable Energy Laboratory
Graphical workflow on top of EnergyPlus — geometry, systems and scenario comparison.
Get it from the vendorWINDOW
Lawrence Berkeley National Laboratory
Thermal and optical properties of glazing systems — U-value, SHGC and visible transmittance.
Get it from the vendor
Blender
Blender Foundation
Full 3D suite — modelling, visualisation and presentation-quality rendering, with Python scripting.
Get it from the vendorThe bottom line
Radiance is the reference tool for lighting and daylight in buildings — free, open source and used on projects around the world.