If you have a teenage Celtic-culture fanatic at home who seeks out Irish dance and music on YouTube, and anywhere else she can find it, you'll know that

Riverdance

, now at the Academy of Music, has gone through several incarnations, touring the world for 12 years to rapturous acclaim. Its squadrons of ultraprecise championship dancers, with their Olympian ability to execute umpteen taps a second in hard-shoe jigs, captivate with their life-affirming vigor.

Through slides, song lyrics, and spoken narrative, Riverdance tells of the Irish connection to land and sea and the challenges of emigration. Its forms have evolved (you can compare for yourself on YouTube or DVD), but the formula still works.

This is spectacle on a rock-concert scale, with sharply focused and flashing lights; with a set bathed in changing colors, complete with staircase for dramatic entrances, and, above all, with contrast and perfect timing. Everything - percussive beats, the funny and the bittersweet - comes at the right moment. The stage fills with thunderous dance from the full ensemble or empties out to home in on one player and the haunting sound of the uilleann pipes.

Musically, the show astonishes. Rich complexity in the harmonies of Bill Whelan's songs recalls Ives or Britten. The fiddle, flute and bodhran (drum) are all rousing and splendidly played. Like all of Riverdance, the tender-hearted optimism of the tunes and rhythms speaks universally, as if underscoring a determination to prevail and find joy.

While Irish dance itself has a circumscribed language - torso held ramrod straight, arms held fast at the sides and parallel legs delivering all manner of taps, ankle rocks and sprightly jumps - it is enriched here through clever staging and by setting it off with contrasting forms, like flamenco, tap and Russian folk ballet.

Rocio Montoya's flamenco performance (sinuous arms at last!) was full of smoldering duende but also an unusual dimension of radiant pleasure. The tappers Jason Bernard and Parker Hall nearly stole the show with their buffooning riffs on traditional Irish dance.

I wish I had enjoyed opening-night leads Marty Dowds and Alana Mallon more. His face was a wooden mask; both were unexpressive, despite being physically up to the dazzling footwork. Fortunately, Dowds relaxed a bit in the second half. With many companies touring simultaneously, finding enough truly stellar performers for these roles is likely a challenge.

At the Academy of Music through Sunday. Information: 215-731-3333 or www.kimmelcenter.org/broadway.