Dom Tower Utrecht

A 21st century light show in this 700-year-old tower describes memories – and inventive design

With an unwritten planning rule that no building should exceed the height of the Dom Tower, it remains the overarching visual signifier of the city.
With an unwritten planning rule that no building should exceed the height of the Dom Tower, it remains the overarching visual signifier of the city.

The narrative is that the light ascending through the tower represents the collective memories of the city

Utrecht’s Dom Tower has stood proud over the picturesque Dutch city for seven centuries, 112m tall and visible from far and wide.
Now Holland’s tallest bell tower is getting even more attention courtesy of In Lumine Tuo, an illumination designed by London lighting expert Speirs + Major as part of a programme to generate tourism through light installations that promote the historic centre. This is no mere floodlighting job however, but a carefully choreographed lighting sequence triggered every 15 minutes and building to a climax on the hour. The result is a rhythmic crescendo of light flowing up the tower before being released in the lantern in a finale of light bursts and bells. 
‘We wanted to create much more than a lit ‘monument’. The tower is a showpiece, the dynamic element, the communicator,’ says Speirs + Major’s Keith Bradshaw, who created the concept with fellow principal Mark Major.

Lighting effects interplay between the tower, the nearby Dom Church with which it was once connected, and the Dom Square where both stand. The narrative is that the light ascending through the tower represents the collective memories of the city. The cooler tone of the lighting effects contrasts with the warmer static architectural lighting.

This design vision was realised with the use of 200 LED luminaires. Bradshaw says it is believed to be the first large-scale heritage use of the technology  and has only been made possible by recent advances which mean much less kit is involved. All the luminaires are co-ordinated by a Pharos control system, programmed by Speirs + Major to achieve the correct sequence.

‘Pharos is a good control system that allows for a stable architectural control system and timeline-based effects,’ says project designer Benz Roos. ‘That combination suited the project. On one hand, the project is an architectural lighting scheme, on the other hand, it is a dynamic artistic lighting scheme.’ 

The task was made especially difficult by the sensitivities of working with a historic monument that severely limited the scope for attaching fittings. In addition, the designers had to make provision for visitors on the tower’s viewing balconies – which affected positions for the lighting kit – while also ensuring easy access for maintenance. In response, Speirs + Major worked with the manufacturer to create custom fittings for the luminaires’ installation that were unobtrusive and acceptable to Utrecht’s heritage inspectors, yet gave the nuanced and spectacular effect they wanted. 

For simplicity, the firm sought to use as few different products as possible. The product specified most often was the Proliad spotlight, used at 3000 kelvins to best suit the brickwork. It has the advantage being able to ‘talk’ directly to the Pharos control system via its DMX controls, as well as being made locally.  They also used products more often found in theatrical applications such as Diversatronics’ strobes & Martin’s Exterior 400 image projector, which could deliver the choreographed sequences. 

Each installation required a custom solution. Emphasising the archway to the tower, two strips of 1200mm-long modules, one either side of the opening, contain 15 Iglu luminaires each from UK manufacturer ACDC and stretch a total of 16m. Here, the designer avoided touching the tower, recessing the fittings instead into an extruded channel in the modern street cobbles. Cabling is housed in this with the luminaires slotted in on top. A relatively harsh light spreads widely from these. 

Half way along the walkway beneath the tower, the arched form of a pair of windows is lit either side by four DMX Cap strobes from Hungaroflash. Here, there was no way of avoiding contact with the tower. But while the boxed luminaires rest on the sills, they are fixed back to modern vertical timber boards in the niches.

To illuminate the arches at first floor level, Speirs + Major took advantage of the lack of public access to sit pivoting Proliad floodlight luminaires on concrete pads on the walkway floor. Eight more illuminate the underside of the niches above the arches that flank the tower. Achieving this unobtrusively was more challenging, since the lights needed to be positioned on the window sill. The solution was a powder-coated galvanised steel clamp system that secured the fitting to the sill without drilling in, with just one fixing to a mortar joint in the wall. The control gear is set well back from street level view behind the pivot.

Illuminations for the stained glass window are mounted on a bar braced in the niche. Light is flashed from different directions to create a vertical movement using a standard Proliad spotlight with a neutral white high output (3000lm) Xicato LED module. DMX-controlled luminaires can flash almost as fast as strobe lights. 

Similar lighting is used on the second floor, although here frosted half moon shields on the front of the Proliad lights soften the beam – designed to a template worked out with paper by Speirs + Major. Without these the short distance between luminaire and tower (0.5m) would produce a very defined spot. 

On the third floor of the tower, the same, floor-mounted Proliad lights illuminate the brickwork niches, but this time in 14 pairs. One is positioned at an angle of 10 degrees to reach the underside of a niche some 30m up, while the other is set at 30 degrees to light half way up the niche and, at the same time, emphasise the detail of the balustrade along the bottom.

At fourth floor level, Speirs + Major installed a total of 33 DMX cap strobes from Hungaroflash on all sides of the bell tower interior – fixed to the wooden clock boards which aren’t historic. These are used for the vertical movement of flashing light during the choreographed sequence, as is the lighting for the bell tower vault on level five. Here, the designers had no option but to touch the historic tower. But contact is limited by mounting three luminaires on each lighting bar, which is fixed at two points into the mortar joints. Two Diversatronics semi-directional high output strobes plus one Hungaro flash strobe, are positioned at different angles for more variation and a punchier, colder effect than the tower’s static mode lighting supplies. 

A major difficulty for Speirs + Major on the six floor exterior walkway was preventing the installation from interfering with the circulation of visitors. The solution was to mount the eight galvanized steel lighting brackets – two on each side – on the metal safety railings. These brackets fix on at three points to the railing and bracing bar and hold Proliad spot luminaires, partially masked with metal plates to reduce sky pollution. Four further installations in each corner niche, away from visitors, employ a vertical pole with three horizontal bars resting on a protective wooden block on the floor. Only the top bar is fixed back while the lower two hold the same luminaires. The base of the balustrade here is lit with LED strips.

The climax of the lighting sequence involves dramatic effects on the underside of the sixth floor spire. Speirs + Major carried out extensive site experiments, even testing a disco ball, before choosing a new LED strobe projector - Martin Professional’s Exterior 400 Image Projector – capable of producing 7000 lumens of the desired theatrical effects in a very cool light. The result is an array of dots conveying the idea of floating memories. Eight of these are mounted on concrete pads in each corner along with 16 Diversatronics semi-directional, high output strobes. Adjustable flash, dimming and output give the display a shimmering effect.

Lastly, at the very top, mounted on the faceted spire itself, Integrex linear LED sources from ACDC with a narrow beam sit in the copper gutter on a bespoke, folded copper bracket that follows the gutter shape and clamps on to it. Its position on the sloped inner surface avoids obstructing the gutter and keeps the product well away from standing water.

The Pharos control system that co-ordinates the sequence is triggered by the tower’s analogue clock to maintain synchronicity with the bells. Total wattage is 0.3W/ft2 excluding strobes; or 1.0W/ft2  including all strobes.

Switched on by Queen Beatrix last spring, the lighting is part of celebrations to mark the tri-centenary of the Treaty of Utrecht, which marked the end of the European War of the Spanish Succession. It is triggered each day by falling light levels at sunset. In static mode, the lighting highlights architectural details of the tower before several minutes of animated sequence preceding each quarter hour. It depicts the idea of the tower as a living organism, says Bradshaw, inhaling and exhaling with the light and setting a new visual soundtrack for the city. 

Its name refers to the Latin In lumine tuo vide­bimus lumen: In your light we shall see the light.


Client City of Utrecht 
Architect Speirs + Major 
City engineer Arthur Klink 
Project manager Kees Van De Lagemaat 
Art consultant Marijke Jansen 
Contractor Heijmans 



Proliad Xicato Spotlight 1300 LM, Spotlight 3000XL
Meyer Custom Superlight Compact
ACDC Iglu, Integrex, Fino
Sill 021 Series Projector, Custom inground uplight
Hungaroflash DMX Cap Strobe
Diversitronics DMX Strobe Cannon
Martin Professional Exterior 400 Image Projector, Pharos control system