Harry, meet Percy

It’s avoiding their example - while following in the financial footsteps of the immensely successful Harry Potter films - that Fox 2000 and director Chris Columbus are hoping for with “Percy Jackson & The Olympians: The Lightning Thief’’ (the longer the title, the better the chances of success?).

Opening Friday, the film is adapted from the first novel in Rick Riordan’s five-book series about the title character, an adolescent New Yorker with ADHD and dyslexia who discovers he’s the son of the Greek god Poseidon.

The six Potter films have taken in $4.5 billion at the global box office, as well as billions more in DVD and merchandise sales - and that’s with two more releases still to come. The first half of “Harry Potter and the Deathly Hallows’’ is scheduled to be released November 19, with part two to follow next year.

Columbus knows his way around the Potter franchise. He rather sludgily directed the first two films, “Harry Potter and the Sorcerer’s Stone’’ and “Harry Potter and the Chamber of Secrets.’’ Will Percy Jackson and Harry Potter have more in common filmically than a director and the same number of syllables in their names?

Logan Lerman, who at 18 is a bit long in the tooth to be playing a character who starts out at 12, plays Percy. Catherine Keener is his mother. Sean Bean plays Zeus. Uma Thurman is Medusa. A seriously bearded Pierce Brosnan is Chiron. And in the most encouraging bit of casting, Steve Coogan holds out the promise of being infernally funny as Hades. (The books have a lot of humor.)

The popularity of Riordan’s series isn’t in doubt. More than 6 million copies have been sold since its debut, in 2005. That does rather pale, though, against the 400 million copies sold for J.K. Rowling’s Potter series.

Quality isn’t necessarily the determining element in a lucrative screen transfer. “The Golden Compass,’’ based on the first volume of Pullman’s trilogy, was quite good. Dakota Blue Richards was a terrific Lyra, and it’s hard to imagine better casting than Nicole Kidman as Mrs. Coulter, or Daniel Craig as Lord Asriel. And “Stormbreaker,’’ the 2006 Alex Rider adaptation, about a teenage James Bond, was as good as some Bond films featuring a shaven Brosnan. Neither movie met expectations at the box office, though.

Story and audience are what count the most, and the two are intertwined. Movies appeal to the kid in all of us - but they can’t appeal too much, or too exclusively, if they want the fullest possible commercial success. And that’s especially true of movies that are literary adaptations. One reason the movie of “The Wizard of Oz’’ was a greater success both artistically and commercially than L. Frank Baum’s book is that it’s so much richer emotionally than the original, a richness that’s either lost or only vaguely grasped by children.

Books that appeal just to children or young adolescents are asking for trouble. Onscreen, Pixar and DreamWorks Animation already do what such books do, only a lot better. They have the grosses to prove it, too. But books that appeal to a larger audience, not just children and teens but grownups, too, hit the audience sweet spot. Hence the enormous success of Peter Jackson’s “Lord of the Rings’’ films or the lesser, yet still considerable popularity of Disney’s two adaptations from C.S. Lewis’s “Narnia’’ series.

It might seem that the more sensible thing for Jackson to have done was adapt Tolkien’s “The Hobbit’’ first, the book that precedes the “Rings’’ trilogy and is explicitly aimed at younger readers. That would have required much less money and, in theory, helped develop an audience for the subsequent films. But whether consciously or not, Jackson recognized that the greater artistic challenge - and commercial payoff - would be the trilogy. It’s telling, perhaps, that rather than doing it himself Jackson is letting Guillermo del Toro direct “The Hobbit’’ from the script Jackson’s co-written.

There’s a demographic sweet spot out there, and should “The Hobbit’’ reach it that would be because of the expectations created by the trilogy. Rowling instinctively hits that sweet spot with her series. The success of the films backs this up. (Pullman, a better writer than Rowling, hits it, too, which makes the lackluster box office of Chris Weitz’s version of “The Golden Compass’’ all the more perplexing.)

The audience question does not bode well for Percy Jackson. Riordan’s plots play off of Greek mythology. He taught the subject to middle schoolers and used the Greek myths as bedtime stories for his son. When he ran out of stories to tell, son asked father to come up with variants. Out of those stories came Percy Jackson.

Rowling has some obvious shortcomings as a writer. She’s never met a modifier she didn’t like, and her mania for plot, while stupendous, is also fatiguing. Rowling also owes a federal-deficit-sized debt to Charles Dickens. But she at least has excellent taste in influences.

Riordan’s books are lively and clever. How clever? Mount Olympus, home of the gods, has shifted to the 600th floor (don’t ask) of the Empire State Building. But they bear no comparison to Rowling’s in imaginative density or literary ambition. Camp Half-Blood, where Percy finds refuge, might be likened to a Long Island Hogwarts. But it has much more in common with the institution of higher learning in “Sky High,’’ a sadly overlooked Disney comedy from 2005 about a school for the teenage offspring of superheroes.

That Percy’s story is so much thinner than Harry’s may derive from authorial calculation as well as literary limitation. Chapter titles like “I Accidentally Vaporize My Pre-algebra Teacher,’’ from the first book, “The Lightning Thief,’’ or “I Play Dodgeball with Cannibals,’’ from “The Sea of Monsters,’’ the second book, are bull’s-eye hits with adolescent boys. They don’t exactly announce themselves as crossover material. All during school vacation week parents will likely be driving kids to multiplexes showing the Percy Jackson movie. They’re less likely to be heading into theaters with them.

If there’s one thing that all these films have in common, from the popular successes like the Potter series and the Tolkien trilogy, to the misses, like “Eragon’’ and “Lemony Snicket’s A Series of Unfortunate Events,’’ it’s their consistent chasteness. No one knows better than Hollywood that sex sells, so there’s no clearer sign of the film industry’s fervor in wanting to build young adult franchises than its willingness to forgo any hint of the licentious in such movies.

Might that be backfiring, though? There is one ongoing series of novels aimed at the youth market that’s so far met with sensational results at the box office. Two films into the “Twilight’’ series, audiences can’t get enough of Stephenie Meyer’s vampires and werewolves. Percy Jackson may have stolen lightning. Meyer’s sanguinary teens have bottled it.

Mark Feeney can be reached at mfeeney@globe.com.