Mark Holland held up two narrow, white glass tubes with seemingly identical bends in them. But the one on the left had a tiny kink in it that rendered the whole tube garbage, he explained.

"This won't work," said Holland, who's been bending these tubes to craft neon signs for 25 years. "If we gave this to the customer, it would go out in a month."

The good tube was part of a bigger project for LifeStyles condoms. The company contacted Urban Neon in Folsom for a flashy neon sign costing thousands of dollars that it plans to hang at a festival.

Neon — long an iconic part of American culture popularized by Vegas-style corridors, beer signs at dive bars, and animated structures atop old-fashioned diners — has made a comeback among big-name companies capitalizing on its nostalgic quality. Posh designers such as Coach and Tiffany & Co. have erected the glowing signs, and Urban Neon has worked on projects for Kate Spade. Showcasing neon, too, are such trendy Philadelphia businesses as City Fitness, which has put up glowing signs with inspirational phrases in its gyms.

But those who observe the industry say the kitschy phrases won't be enough to sustain the neon business in the region long-term, as cheaper LED (light-emitting diode) lights have taken over, and only a handful of glass benders such as Holland are left here.

"To stick a couple of signs in a window, it's cute, but it's not particularly nourishing of neon," said Len Davidson, a neon expert who lives in Fairmount. "It's fashionable in a sense. … There's still some demand, but the level is not the same."

>> PHOTO GALLERY: Philly's last neon sign makers

Still, loyal customers in Philadelphia swear that no matter the cost of routine repairs, they won't replace their neon with LED.

LED "has a different glow, it has a different color to it," said Ken Weinstein, who owns the Trolley Car Diner in Mount Airy, which has an animated neon sign. "I appreciate it might use less energy. But it's just not the same."

The slow disappearance of neon signs is a bit of a chicken-and-egg situation. There are few people left who can create neon signs from start to finish, making it difficult for businesses to maintain such signs. Davidson estimated there are fewer than a dozen tube benders in Southeastern Pennsylvania and South Jersey.

Ray Mckenna, who owns Inter-State Signs in Abington, stopped paying in-house tube benders several years ago after work had dwindled to just two pieces a month. And Spectrum Neon in Pennsauken, which employed eight glass benders as of 15 years ago, now has just one. Still, the owners say, neon makes up about 75 percent of their business, though most of that is restoration and repair work.

After neon signs became popular in the 1920s, there were schools to learn the craft of tube bending. But most shut their doors by the '70s, so today's neon artisans have learned the old-fashioned way: apprenticing for years under someone else.

The process of creating a neon sign is an intensive mix of art, chemistry and mechanics. It involves designing a pattern, bending the glass, processing it with the right concoction of neon, mercury, and argon to get the perfect color, and then blasting it with electricity.

Basic beer signs can take a day or more of labor. Even benders like Holland, who have made careers out of holding glass tubes over an open flame, routinely make errors. Great benders use all their senses to construct the signs, developing an ability to smell when something's off.

Which is all to say that making neon signs isn't cheap. It can cost a couple hundred dollars merely to have a small sign repaired.

Mckenna said LED — first introduced as a lighting alternative that uses five times less energy than neon — has now become cheaper than neon, too.

"I could not compete in the market if I used neon," he said. "A letter would cost me about $4 in LEDs but $100 in neon."

Urban Neon owner Domenic Urbani said that, in many cases, the company recommends clients move toward converting to LED, to save them money and time. Urbani isn't thrilled about it. He's a trained glass bender and was anti-LED at first. Eventually, he "came around because clients insisted on it."

Bobby Simone Jr., Spectrum's head tech and the son of its founders, said most of the company's work nowadays is larger signs that are local, such as at the Geno's outpost in the airport and the glittering signs that adorn Xfinity Live! in South Philadelphia. But the volume from small businesses has drastically decreased.

"It's a shame," he said, "that it will eventually become a lost art. You can't replace that look, that cowboy with the thumb on the Las Vegas Strip. LED can't do that."

Davidson said aesthetics have changed for the storefronts that remain. The heyday of neon, he explained, was when companies had picture logos and created spectacular, animated signs depicting their brand. Today, fewer companies have intricate logo designs. Beyond that, plenty of folks just don't have the same level of appreciation for hand craftsmanship, and others perceive the signs as tacky.

Now, more often, store owners replace neon borders with LED lights that Mckenna noted, ironically, "look like Christmas."

At two City Fitness locations, the company hung neon signs with such slogans as "You are not alone" and "You made it," and it will likely use them more in the future as it expands, according to Tom Wingert, the company's vice president of marketing. He said it's about bringing close something once reserved for high in the sky, a move that feels especially effective in the Instagram age.

"If somebody feels like something special is happening, they're going to have a more powerful experience," he said, "and I think neon has that effect when you bring it down to eye level."

Plenty of iconic neon signs remain in Philadelphia, too. On South Broad Street, there's the Boot and Saddle sign, which was restored in 2015, and in South Philly, Termini Bros.' red-and-green beacon looms over Eighth Street.

In Center City, the glowing red neon sign that marks the front door of McGillin's Olde Ale House on the otherwise dimly lit Drury Street is "like a lighthouse in a storm," said owner Chris Mullins Sr.

McGillin's has had a neon sign since the 1930s, and though Mullins admits that the current sign is "maintenance-intensive" — trucks routinely back into and damage it — he wouldn't consider cheaper LEDs.

"As far back as anyone remembers," he said, "there's always been a neon out in front of McGillin's."

Weinstein, of the Trolley Car Diner, has effectively doubled down on his neon. He's planning to open another diner in Germantown in mid-2019, complete with a neon sign for the top.

At the original Trolley Car, "we've converted every other light inside and outside to LED," he said. "So our last holdout is our neon sign. And I'm OK with that."