Postcards From Vegas: Rob and Nick Carter's fluorescent glowing glory

The works in Rob and Nick Carter's new exhibition ought to be garish. Instead, they're gorgeous. "Sin Will Find You Out", declares a condemnatory neon crucifix, overlaid on a hyper-enlarged old postcard of America's Spaghetti Junction: an interchange on the Eisenhower Expressway near downtown Chicago. It might as well be an entry in one of those novelty Boring Postcards books. The crucifix, meanwhile, is a miniaturised recreation of a sign that still hangs from a Christian mission on the West Side of Manhattan.

Similarly incongruous is the "TOPLESS" neon (from the Desert Flame Strip Club at 11145 Apache Trail, Arizona) superimposed on a postcard of some gruff-looking beefeaters at the Tower of London. Fourteen of these compositions – some funny, some faintly baffling, all sumptuous – make up Postcards From Vegas, the Carters' fabulous new London show, their first since 2007. "As we started to make them," says Rob, "it became clear that the two separate elements, postcards and neons, look pretty kitsch. But put together, they feel very contemporary."

Since they married and began working together in 1997, the Carters have always used light as their medium; their first collaborative work involved sweeping neon tubes across photosensitive paper to produce painterly colour marks. They've made huge, interactive public artworks, and pieces small enough to hang in the hallways of such luminaries as Jude Law, Matthew Williamson and Sir Elton John.

The neons in Postcards From Vegas are all existing signs, remade in metre-high (or thereabouts) miniature. The postcards are Cibachrome prints, blown up to match, and thus revealing some of their charming details: creases, pin-marks and inexpertly hand-tinted colours. While most of the neons are based on signs in Las Vegas, the places evoked by each piece are unreal, located somewhere in the past of the collective imagination. "People don't send postcards like they used to," says Nick (Nicky to her friends). "When we were younger, they were the best way to get an image and an idea of another place."

Originally, the couple conceived a mash-up of neons and original photographs, then Rob recalled his youth. "I used to keep every postcard I was sent, and if I went round to a friend or relative's house and they'd been sent postcards, I'd nick those too. I lost interest when I got old enough to be interested in girls, but I phoned my mum to check if she still had my collection, and she dug them out of the attic."

The pair put together around 150 computer mock-ups of postcard/neon combinations, editing their selection until they agreed on the 14 that make up the show. Their initial considerations were aesthetic, says Nick, but they both developed differing textual interpretations of each piece. They're reluctant to reveal them, though: "You're meant to draw your own conclusions," says Nicky.

Helpfully, art critic Alastair Sooke has drawn some in his introductory essay to the exhibition catalogue: "These juxtapositions have a surreal, nonsensical quality," he writes, "not unlike those witty paintings by Magritte in which words do not match the images they label." And yet, "There is also a subtle correspondence ... after seeing Pioneer Pawn, it is impossible to look at Neuschwanstein Castle without thinking of the overblown casinos aping far-flung architectural styles in the Nevada Desert ... This is the world we live in, where culture is co-opted for tawdry ends."

More than anything, the works are beautiful objects: moreish, narcotic even – and dangerously collectible. "Considering neon is a 100-year-old technology," says Rob, "the quality of light it produces is still pretty much unrivalled. In terms of the colours they generate, LEDs have nothing on neon."

Postcards From Vegas opens today at the Fine Arts Society, 148 New Bond Street, London W1, and runs until 15 February. For more information, go to www.robandnick.com