Brian Maier, 37, said using his Samsung Galaxy Note 5 to read the menu at a Tex-Mex restaurant in Austin, Texas, made his mind flash to a late-night commercial for a credit-card-sized magnifying glass with a light featuring white-haired actors.

“It made me feel like, ‘have I reached that stage of my life, where I’m that elderly person?’ ” he said.

Dinner has gotten darker, said Andrew Knowlton, the 44-year-old editor at Bon Appétit magazine, who has eaten in roughly 400 restaurants annually for nearly 15 years. When he began his career, restaurants were generally split between upscale places and “mom and pops,” he said. Now, more restaurants are competing in the in-between zone, expected to provide good cuisine and a fashionable atmosphere. He said that turning the lights down is a quick fix for those with lower budgets.

Mr. Knowlton said he finds it embarrassing when other diners—even worse- his dining companions (“I’m going to give my wife up,” he said)—resort to the cellphone solution. He vowed he would never succumb. “I’d rather give up restaurants.”

Television host and comedian Scott Nevins, 37, once took an equally hard line, mocking friends when they resorted to the cellphone flashlight while dining out in San Francisco, New York, and Los Angeles, where he lives. Then he ended up in the hospital after eating some undercooked chicken in a restaurant.

Since then, Mr. Nevins wouldn’t dream of putting a piece of chicken in his mouth before an analysis aided by his iPhone—“on full high beams, as you could land at LAX,” he said. His mortified friends groan and threaten to abandon him at the table. “I always say, ‘Oh, be quiet. It’ll be three seconds,’ ” he said.

The ideal way to balance atmosphere and legibility is two-pronged, said David Rockwell, an architect who has designed restaurants including Nobu and Union Square Café in New York. One set of lights along the room’s perimeter or ceiling sets the overall ambiance, while each table also gets its light to enable diners to see close up.

That’s expensive and hard to perfect, which is why some restaurateurs celebrate the cultural shift in which patrons arrive packing their lanterns.

“It means restaurants don’t have to worry about it,” said Marc Dix, food and beverage manager for Granville Restaurant Group, which has four restaurants in Los Angeles. “They can just go ahead and create the atmosphere they want.”

Though Granville staffers try to help diners who complain by bringing extra candles or even aiming their cellphone flashlights at menus, one thing they won’t do is turn up the lights.

“We do get a couple of complaints about noise level and darkness,” Mr. Dix said. “But that’s the vibe that keeps everything going.”

In Scottsdale, Ariz., when David Gottlieb and his wife, Miriam, took their seats on the patio of Local Bistro, they quickly turned on their phone flashlights. When he looked up, Mr. Gottlieb said he saw other patrons doing the same. “There was no shame in it,” said the 72-year-old software engineer. “There was no other way to read the menu.”

Mr. Gottlieb said it was so dark that when he put down his phone to eat, he couldn’t tell whether he was stabbing steak or potato with his fork.

Laura Osio, marketing director for Osio Culinary Group, which owns Local Bistro and two other restaurants in Scottsdale, stands by the secret sauce of dusky ambience. “Diners prefer to have a more intimate atmosphere at dinner, which is created by dimming the lights,” she said, adding that lighting complaints are rare.

Stephani Robson, a lecturer at the Cornell School of Hotel Administration, said her research has shown changing the lighting doesn’t change what people order. But she said restaurants probably cling to the concept because a “yellow, firelit glow” makes both people and food look better.

Moreover, diners don’t hesitate using their smartphones for just about everything else, said Greg Sage, operating partner, and general manager for Ocean Prime steakhouse in Beverly Hills.

“They text, check email, check reviews of the restaurant they are in,” he said. “I walk by and see that they are trying to figure out what to order from Yelp.”

Write to Katy McLaughlin at katy.mclaughlin@wsj.com and Anupreeta Das at anupreeta.das@wsj.com