L’Acte Lumière receives an « IALD Award of Excellence » for the lighting design of Strasbourg Cathedral

The Cathédrale Notre-Dame de Strasbourg is not a building you illuminate. It is a building you reveal. The extraordinary depth of its stone fabric — successive layers of arcades, buttresses, tracery and sculpture accumulated over eight centuries — demanded an approach from within, not from outside. The light does not land on the surface. It enters the thickness of the masonry, and shadow becomes the material of composition.

The Vosges sandstone carries a rich chromatic gradient, from ochre to brown to red-violet, precisely where most LED sources perform at their worst. Careful colorimetric calibration was required far beyond standard specifications: dominant wavelength 581.9 nm, colour temperature normalised at 2700 K, chromatic distortion below 2 MacAdam ellipses. The result shifts from 2700 K on the exposed outer surfaces to 2200 K in the deepest recesses of the stone — a warmth that seems to have accumulated in the cathedral over centuries, not installed over eight months.

The lighting reads differently at three moments of the night. At dusk, every sculpted detail is fully revealed. At 10 pm, at the sound of the Zehnerglock — the historic bell of ten o’clock — intensity softens and the eye is invited upward toward the spire. After 1 am, only the upper tower and the rooflines remain lit: a quiet, reassuring presence above the sleeping medieval city.

The project brief imposed total reversibility: not a single element of the installation was to result in a hole in the historic stonework. Every one of the 580 LED fixtures — spanning 8 families from 3W ground-recessed units to 300W long-throw projectors — was attached exclusively into the mortar joints. Every one of the 14 km of cables. Every custom bracket, clamp and collar, designed and fabricated for each individual fixing condition, painted on site to match the colour of the sandstone. Eight months of site work, including rope-access interventions across 142 metres of elevation. Not a single fixture visible from the public spaces around the building.

The system is controlled via DMX through 9 distribution nodes, with individual dimming on every circuit. The installed power stands at 15 kW; effective operating power at 10 kW — a 44% reduction against the previous installation, against a contractual requirement of 10%. All light lands on the stone surfaces of the building. None reaches the night sky.

The cathedral lighting is the culmination of the Strasbourg Plan Lumière for the Grande Île, classified as a UNESCO World Heritage Site. The adjacent Place du Château — also designed by L’Acte Lumière, delivered in 2014 and recipient of the City People Light Award that same year — was conceived as the deliberate antechamber: subdued, restrained, so that the cathedral could breathe above it. Two years later, the logic proved right.