The praise for the recent lighting of City Hall has been glowing. Too bad the lights aren't.

Instead of gently illuminating Philadelphia's great beaux-arts centerpiece, the new lights turn it into a shadowy, Gothic horror house. Fixtures perched on surrounding rooftops send blazing 2,000-watt beams shooting into the night sky over City Hall. The flares are so intense you can be forgiven for assuming that the place is a giant crime scene - which, in fact, is exactly what federal prosecutors allege. You half expect James Cagney to come running across City Hall's Second Empire roof, bellowing "Top of the world, Ma. "

This, of course, was not the effect that the designers at the Lighting Practice in Philadelphia were seeking when they tried to lift City Hall out of its gloom. All the old architectural lighting had been stripped from its marble walls in preparation for a marathon power-washing, leaving the full-block building in the dark. The aim of the project, spearheaded by the Center City District, was to celebrate the newly cleaned facade by showering it with light.

Without a doubt, City Hall and its plaza are brighter today, but in all the wrong ways. Because the light fixtures radiate such powerful beams, our eyes can't help but be drawn up to the source. We're as spellbound as the characters in Close Encounters of the Third Kind. But instead of an alien craft in the sky, there is a mess of lighting hardware on top of Philadelphia's most historic towers. Looking at the fixtures, which range from 150 to 2,000 watts and are known as "space cannons," is like gazing directly into the sun.

James B. Garrison, the Hillier architect who renovated the adjacent tower now occupied by the Ritz-Carlton Hotel, said he was so shocked by the prominent fixtures that he initially thought they were temporary structures. They're not. "They seem very insensitive to the architecture," he observed.

For all the light-emitting power of those rooftop fixtures, the illumination on the ground is oddly uneven: City Hall tower and the building's north and east facades have a pleasing, even glow. But the west facade is patchy with shadows, and the south side looks as if it is experiencing a lunar eclipse.

The problems with the City Hall lighting should be a cautionary lesson for Philadelphia, which is about to embark on a new lighting scheme for Boathouse Row and for the buildings around Washington Square. In recent years - as the memories of the '70s energy crisis have dimmed - cities have discovered that lighting buildings is a cheap way to dazzle. Not only does illumination dramatically set off architectural gems, the added brightness makes downtowns feel safer. Despite the flaws, there's no doubt that the City Hall lights increase the public's comfort level.

But lighting a building properly is harder than it looks. And there is probably no building in Philadelphia more challenging to illuminate than City Hall, with its undulating folds of columns and sculpture by Alexander Milne Calder. Though City Hall stands alone, it is hemmed in by a tight circle of towers.

The Center City District gave the task of lighting the massive structure to Alfred R. Borden 4th and Julie M. Panassow, both experienced designers. Several years ago, Borden turned 30th Street Station into a beckoning oasis with an artful mix of backlights and uplights. The two designers also elegantly highlighted the architectural details on Logan Square's civic buildings and the Philadelphia Museum of Art.

Those projects were successful because the designers didn't attempt too much. In each case, they selected a few key architectural details and emphasized those. With the Free Library and the Art Museum, that meant inserting lights behind their main colonnades to accentuate the sculptural presence of each column.

But because City Hall is the physical and spiritual heart of Philadelphia, the CCD and the designers decided the building deserved a more deluxe treatment. In their initial design, prepared in 2000, Borden and Panassow proposed a $3 million combination. There would be small fixtures attached to the building to dramatize City Hall's rich sculpture, and large rooftop fixtures to bathe it in a uniform light. By the time the job was approved, the budget had been slashed to $800,000. All the detail lighting was eliminated.

Apart from the money issue, the idea of ringing City Hall with high beams was a bad idea. Because surrounding buildings hug the edge of City Hall, the designers were never able to get the right angles necessary to illuminate all four facades, despite using 69 large metal halide fixtures.

In fact, the staff reviewers at the Historical Commission initially denied permission for the fixtures because they felt the giant hardware would be too prominent. They preferred to see the same detail lighting used on the Art Museum. But the staff was overruled, first by commission members, and then by the state historical agency. Now their concerns have been borne out.

Paul Levy, head of the CCD, acknowledges some of the problems, but he argues that even flawed lighting has dramatically improved City Hall's nighttime presence. "We had a situation where we couldn't get perfection," he said. And Borden added, "all in all, we're happy. " In time, Levy hopes to add more detail lights on the facade. What's really needed, he added, is a comprehensive plan for pedestrian lighting and landscaping for City Hall plaza.

More lighting isn't necessarily better lighting. The best architectural illumination is where you notice the building, not the lights. All you remember is the glow.

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Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com. Read her recent work at http://go.philly.com/ingasaffron.