It's been a strange week for pop music. The deeply unconvincing Ke$ha was reduced to drinking fake blood from a heart onstage in Australia in a bid for some edge. A 13-year-old girl called Rebecca Black became an ironic internet meme when "Friday", her cheesy pop video made courtesy of a bespoke service called Ark Music Factory, went viral and clocked up 10m YouTube hits.
Meanwhile, Justin Bieber – the most followed pop pup de nos jours – wasn't really the star of his own show. As the teen idol kicked off the first of three nights at London's O2 Arena, the eye of at least one over-12 kept wandering to the majestic sight of umpteen coloured devices – glow sticks, mobile phones – lighting up the audience, like a mass of bioluminescent plankton moving on the night sea.
That's not to suggest that Bieber is dreadful. Mostly he is just fine – all shiny himself in a series of blinged-out urban-lite tracksuits. He's not a bad dancer either, even if he executes his moves with drilled skill rather than natural elan. It's in contrast with his opening act, Willow "Daughter of Will" Smith, a gangling 11-year-old who resembles a streetwise string bean in bright green and black. She's only on for 14 minutes – due, you suspect, as much to the UK's strict child performance licence laws as her dearth of material thus far – but she fizzes with physicality. "Whip My Hair" – a sensational novelty single – is wonderfully manic; its overcooked sequel, "21st Century Girl", less so.
The most whizz-bang thing about Bieber's over-scripted and slightly workaday show is the hydraulics. A series of flying contraptions ensures that anyone here with even the most germinal of mothering instincts (and there are probably 23,000 of us, give or take a few dads and brothers) forgets to breathe as Bieber is repeatedly lofted high into the air and dangled over the crowd like bait. One contraption is a heart made of bits of scaffolding, in which Bieber plays surprisingly competent acoustic guitar for "Favorite Girl" – the kind of emotionally explicit swoon-fodder in which teen idols have long specialised. Bieber's slightly punchier R&B numbers are a little more fun.
Throughout it all, Bieber remains stoic, gazing out at his public with a kind of neutral professionalism that could just be a suppressed fear of heights. Disappointingly, there is little mischief to Bieber, no spin, precious little flirtatiousness, and zero winks. Is he enjoying himself up there? It's probably the only few minutes' peace he gets on his own all day.
Smaller details of his performance intrigue. Who would have thought that Bieber's backing singers would resemble a barbershop quartet recruited from the yakuza? The mystery of the finger-snapping far eastern hard men stage left is solved when Bieber reveals that he discovered Legaci – for that is their name – on YouTube. "Like I was discovered on YouTube!" he points out.
And what is Craig David doing here? The urban crooner comes on in the encore, introduced unenticingly by Bieber as "someone your parents might like". He performs his hit "7 Days" –, the very first time the notion of sex is broached tonight. "We were making love by Wednesday/ And on Thursday and Friday and Saturday/ We chilled on Sunday," it goes. Bieber eventually joins David, singing along to the chorus. If you watch his lips closely, though, he misses out the line about Wednesday entirely.
It all ends with the infernally catchy "Baby", a song that takes the most clichéd romantic pop trope to the limits of sense. "Like baby, baby, baby, ohhh," croon the Beliebers. There are those who would argue that tween girl fandom is active, creative and rewarding rather than passive and supine (all those hand-lettered posters, all that bonding). But you can't help but wonder what a musical world would sound like, in which all the inchoate longing of preteen girl lust was channelled into learning how to play guitar.
Or, alternatively, into creating an alternative, blue-haired, sugar-crazed, proto-vegetarian Wonderland. Katy Perry's California Dreams world tour is everything that Bieber's is not – silly, brightly coloured, theatrical, fun and very down on butchers. Even though her audience is only slightly older than Bieber's, Perry's Pierre et Gilles-in-a-sweet-shop theme has a lysergic edge to it, made plain when Perry bites into a "special" brownie proffered by a couple of mimes. She starts having funny dreams about following her Kitty (no relation) and fancying gingerbread men, all relayed on screens that progress the show's notional plot during her frequent dazzling costume changes.
I've never been a fan of Katy Perry, balking at the shock-tactic fake queerness of "I Kissed a Girl" and seething at "Ur So Gay". "California Gurls" remains a rotten song. But for all her gimlet-eyed calculation, Perry packs more wit and charisma into her eyelash extensions than most pop stars manage in a career. Tonight, "I Kissed a Girl" has a dramatic 60s torch song makeover; even "Ur So Gay" is forgiven.
Bieber's broadcast home videos make it clear he was a born show-off; Perry is a born entertainer, gabbing lucidly all the way through a bravura two-hour performance. The beautifully-lit Beliebers were the real stars of Bieber's show, but Katy Perry makes you actually believe in the ridiculous transformative spangle of pop music all over again.
