Congregation of light.

Its fluid spaces animated by an exquisite combination of natural and diffuse light, Steven Holl's sculptural Jesuit chapel uses illumination as a powerful metaphor for spiritual life.

The Chapel of St Ignatius by Steven Holl provides a welcome antidote to the technological, pragmatic and secular focus of much current professional practice. Conceived as a metaphorical gathering of different lights, this building is a quiet reminder that our most important values are riot market driven and that meaning is still possible in architecture.

While Holl characterises the scheme as a space-making rather than an object building, it is in fact both. Located at Seattle University, a private Jesuit college of approximately 6000 students, the building is carefully positioned to define four new quadrangles in a developing area of this urban campus. On the site plan, the orthogonal footprint of the chapel and the exterior spaces which it helps to define are indeed indistinguishable from other buildings and spaces which make up the campus fabric. However, in reality, the extraordinary sculptural roof forms of the new chapel together with the pared down iconography of cross and bell tower clearly endow the building with object status.

By day, the chapel is understated, giving few outward and visible signs of its inward and spiritual grace. The metaphor of light refers specifically to St Ignatius' vision of the many interior lights and darknesses comprising spiritual life. Holl has conceived the building as 'seven bottles of light in a stone box' (AR November 1995). The vessels are represented by six distinct roof volumes held within an orthogonal perimeter wall; the seventh vessel is a reflecting pool. While this order is comprehensible from without, no amount of external study or even examination of architectural drawings, models or photographs can fully apprehend the nonrational space within. The fluid, aqueous space explored in the Stretto House is here developed into a rich, complex interior, a built metaphor of spiritual life.

Notwithstanding its interior complexity, the plan is disarmingly simple. Support spaces around the perimeter of the building form an inhabited thick wall which encapsulates the primary space of worship. Ochre-stained interlocking tilt-up concrete panels, cast on the slab and lifted into place, give the building a modest outward demeanour. A lawn and reflecting pool to the south create a processional forecourt leading to the chapel entrance.

However, Holl deftly twists the conventional expectations set up by the site plan and the rectangular volume of the building. Although movement occurs along a longitudinal axis, it is not central but is shifted to the edge along the west wall. The entrance, located at the south-west corner of the building, is casual, an eroded corner alongside the campus footpath. The climax of the long axis of the building is not the altar but the tabernacle in the small Blessed Sacrament Chapel. En route to the tabernacle, movement is inflected by the baptismal font. This inflection sets up the rotation of the main chapel onto a cross axis which places the altar - both in keeping with tradition and, in this case, unexpectedly - to the east.

The fluid quality of the interior space is achieved by manipulation of the building section. Light - admitted, shaped and coloured by a myriad of means complements the formal intricacies of the space. Although apparently complex, there is a system of underlying order. All windows are golden sections and have a similar proportional relationship to the rooms within. The windows, articulated as gaps between the concrete wall panels, therefore determine the location of the panel joints. Moving from the entrance into the chapel, there is a progression from clear glass offering exterior views, to translucent glass with obscured views, to coloured light from hidden sources. With these modest devices, Holl represents the transition from exterior to interior, from activity to reflection, and from physical world to spiritual realm.

Colours of light always occur in pairs: a small lens of coloured - or stained - glass. admits light directly, while a second larger area of colour is admitted indirectly by reflection from painted surfaces concealed by baffles. Although the strategy can be easily understood if analysed, the simple concealment of both light source and painted surface creates mystery, a sensation all too rare in this scientific world. The confessional, with an alarmingly intense orange lens in a field of purple reflected light, even shocks at first sight. These effects are not fixed but transitory, fluctuating in intensity with changing conditions of weather and shifting across the rough white walls and the polished concrete floor as the sun moves through its daily and seasonal cycles.

At night, light transforms the introvert into exuberant extrovert. With indirect artificial lighting, colour from the painted baffles is reflected outward, changing the translucent roof lights into colourful beacons in the night sky. The coloured glass lenses undergo a similar transformation: red glass is neutralised by complementary green reflected light, and yellow glass superimposed on reflected blue yields green. Roof lights face different directions, calling students to evening worship from all parts of the campus. For night-time services, darkness within is emphasised. Blown glass light pendants and sconces can be dimmed to the illuminance level of a single candle, and backlit baffles provide backdrops of sumptuous coloured light to different areas of the chapel.

Perceived weight and weightlessness - the stone and the feather - are considered by Steven Holl as interdependent opposites, neither capable of being fully understood without the other. While these attributes are clearly differentiated in the Stretto House, their relationship in the Chapel of St Ignatius is ambiguous and full of tension. The interior of the building hovers between reading as space carved from a monolithic, weighty mass and a clad assemblage of planes. Externally, the weight of the concrete wall panels with their deeply recessed joints is counterbalanced by otherwise taut detailing. The hinged corners of the building, which would typically connote mass, are in Holl's hands now familiarly understood as thin cladding to void space. Zinc roofs meet concrete walls at a knife edge; both materials are infinitely thin, revealing neither substance nor depth.

Yet, the tactile qualities of materials - rough plaster, cast glass, hewn wood, and gold leaf - are compelling. Visitors are drawn to touch these surfaces, not casually, but slowly and with reverence. Indeed, the richest aspect of the intertwining of sensory stimuli with both experience and imagination is the degree to which the craft of the human hand is revealed. Together with the explicit iconography of Catholicism, the building offers another iconography - the texture of the trowel, the irregularity of blown glass, and the mark of the chisel - of the human potential to create beauty with imperfection, surely an inspiration to all who enter.