Who knows, maybe designing lighting around an architectural project by Rogers Stirk Harbour + Partners, the international firm of British high-tech wizard Richard Rogers, would bring with it a sense of terra incognita. But when lighting designer Maureen Moran's turn came along, rather than be stymied by the proposition, she embraced it, suspending a number of things learned in the 30 years she has spent working around rather conservative clients in the Washington, D.C., area.

Rogers' first foray in the nation's capital—300 New Jersey Avenue—takes two older limestone and brick buildings and turns them into a trio. The three buildings triangulate around a new 12,000-square-foot Rogers'-designed glass atrium that soars a full seven stories, which Moran's firm, D.C.-based MCLA, was hired to light.

In this atrium, you know Rogers is your host: Its glass roof juts out severely like a blade's edge over the deep forecourt of the complex, supported by a finely machined and cabled structural “tree.” Rising from the ground at the atrium's heart, it is painted yellow, with two enormous trusses reaching as limbs to undergird the roof's far edges. The tree's smaller, lower branches embrace a glass elevator shaft and support a layered network of open stair platforms and illuminated glass bridges that cross to the two adjacent buildings.

Those already familiar with Rogers' work may find this space relatively simple. Those who aren't may liken it to a structure that has been pieced together in a game of mousetrap. The project, completed in collaboration with the architecture firm HKS, is all the more remarkable because it captures a dead-on view of the U.S. Capitol and also because hardly any Washington office developers, given the District's strict height limitations, bother to produce large, dramatic atria.

But JBG Cos., the client who developed the project for the principal building tenant, the law firm Jones Day, was smitten enough with Rogers to indulge his signature forms of expression. Moran seems to have enjoyed this expressiveness as well, though it also likely took her aback after having worked with so many buttoned-up D.C. building tenants. “Everything's so exposed,” Moran says, referring to the structure as well as her lighting. “Where we get our hands slapped on some projects is where there's a socket shadow.” But that wasn't a problem with Rogers' firm. “They love seeing stuff exposed.”

To complement the bravado of Rogers' architectural structure, Moran did not use a lot of fussy illumination. The lighting is largely surgical in its precision, appearing only where absolutely needed. Upon entering, you note, without great distraction, a discreet path of small, circular LEDs recessed in the plaza's stone tile floor. Starting at the sidewalk and continuing into the lobby, these uplights are an introduction to Moran's legato sense of the space. By day the atrium drinks in plenty of natural light, and at night it borrows a good deal of referred wattage from the surrounding office windows.

The most intense concentration of lighting occurs around the structural tree and its limbs. Once you're inside the atrium, the most visible fixtures are linear T5 fluorescents that delineate and highlight the undersides of the glass bridges and the floating terraces. Viewed from below, they appear amply but not shockingly bright, mainly to illuminate the walking surfaces of the bridges below.

A clear sense of Moran's discretion in lighting is found in the open stair. Here, along a secondary structural column, she integrates 65 feet of vertical translucent piping that draws light from two metal halide sources, one lamp at either end. An inner film disperses the light along each column's height. The lighting is perfectly adequate and evenly spread along the rise, but unless you look hard for it, you may miss the actual source.

One minor blip in an otherwise unobtrusive installation is the alignment of the vertical piping modules at their joints as you look up the column. Ever so slightly crooked, they read as more segmented than Moran likely wanted.

It's easy to surmise the effect Moran was after by looking at the simplicity of the scheme. The atrium's south side is lit by circular metal halide fixtures set flush with the floor and trimmed in stainless steel, which train their light up onto a limestone wall that used to be the exterior of the complex's 1935 building. The projection dignifies the handsome façade and leaves a soft reflection for the surrounding open space, where the floors are a dark color.

For events and functions that might require additional lighting, Moran installed practically invisible sets of accent lights at either end of the atrium's upper ridge near the roof. These fixtures play into clusters of reflective mirrors to produce diffused ponds of light rather than riveting rays. Even where and when Moran's lighting does not announce itself prominently, her critical thinking comes through—as at the atrium's entrance, where you can see plenty of light but are not standing in it. Rather than fire up the place heavily and risk over-dazzling, she keeps the lighting trained on the dynamic architecture to show it to its best advantage.

Bradford McKee is a writer in Washington, D.C., who covers architecture and design.