What If Your Lighting Simulations Are Wrong?
New research raises questions about photometric accuracy in industry-standard formats
For more than two decades, lighting specifiers have relied on the same fundamental approach to predict how installations will perform. Lighting design software has become the trusted standard, backed by industry leaders and used daily by thousands of professionals worldwide.
Photometric data flows from manufacturers into calculation engines that promise accuracy within tight tolerances. Projects worth millions of dollars proceed based on these simulations, and nobody questions the underlying assumptions — until the lights turn on and reality doesn't match the render.
But a peer-reviewed study published in LEUKOS last month suggests something troubling: under certain conditions, lighting simulation tools may not be as accurate as expected, due to legacy data formats that reduce complex luminaires to simplified point-source representations. The consequences aren’t purely academic. Some designers may already be encountering unexpected dark zones or glare problems that weren’t predicted by their simulation tools.
The Reach of the Problem
The researchers used DIALux and RELUX software applications — widely used in Europe — to model three types of luminaires and compare results against calibrated lab measurements. While the study focuses on these two platforms, the underlying issue lies in the structure of standard photometric file formats. That raises an open question: if AGi32 and Visual in North America also rely on IES file formats with similar geometric assumptions, could comparable simulation errors be present across all major platforms?
The LEUKOS paper doesn’t test those North American tools, but it does highlight fundamental limits in how traditional file formats represent spatially complex luminaires. As such, it’s reasonable — though unconfirmed — to consider whether the challenge extends across the board until enhanced data formats are more broadly adopted.
A Closer Look at the Errors
The research, led by Marek Mokran at Slovak University of Technology, tested three luminaire types against laboratory measurements. For compact fixtures, DIALux and RELUX delivered relatively accurate results — deviations stayed within 2–6%. But for luminaires with multiple spatially separated light sources, errors rose sharply. In one tested configuration, deviation exceeded 30% at a 1-meter offset — a scenario not uncommon in certain classroom or office settings. Even standard linear luminaires showed consistent 6% deviations at one-meter off-axis positions, which often correspond with task surfaces.
To be clear: not all typical installations will suffer large errors. The most significant deviations appeared in near-field regions (within ~1 meter) and with specific luminaire geometries. At standard mounting heights around 2.5 meters — typical in offices — the study reports that deviations often fell to within 1–2% for linear fixtures. But the potential for larger errors remains, particularly when designers rely on simulations involving complex luminaires at close range.