Robert Irwin, a Southern California artist associated with the Light and Space movement of the 1960s, who early on stopped making paintings in favor of creating ephemeral and sometimes intangible art environments, died on Wednesday in the La Jolla section of San Diego. He was 95.

His death, at Scripps Memorial Hospital, was caused by heart failure, said Arne Glimcher, the founder and chairman of the international Pace Gallery, which has shown Mr. Irwin’s work since 1966. Mr. Irwin lived in San Diego.

Within the contemporary art world, Mr. Irwin’s work on human attention and perception — he called it, with a nod to scientific research, an “inquiry” into perception — was highly influential; he won a MacArthur “genius” award in 1984.

The work was not highly visible to the public, however. Until the late 1970s, he did not allow his projects to be photographed. He long gravitated toward site-specific works that were temporary in nature, like the time he drew a square on the ground with string for the 1976 Venice Biennale.

And even with his more permanent works — like his design of the Getty Center garden in Los Angeles for its 1997 opening, or his work as the master planner behind the Dia Beacon museum in upstate New York for its opening in 2003 — it can be hard to identify his handiwork. (It can be challenging, for example, to distinguish what exactly he contributed to the Dia building renovation versus what he discovered on site.)

But that kind of parsing may be beside the point. Mr. Irwin identified his goal — and the underlying goal of modern art generally — as awakening viewers’ powers of observation and concentration so that they become active participants in the experience.

“Irwin’s work is not about a particular medium — so he can do a garden, a scrim piece, a piece of string on the ground,” said the writer Lawrence Weschler, who made Mr. Irwin’s sometimes abstruse philosophic approach to making art accessible in his book “Seeing Is Forgetting the Name of the Thing One Sees” (1982).

“Having said that,” Mr. Weschler continued, “there’s a laser beam consistency to his essential project throughout his career: trying to get people to perceive how they perceive.”

Or, as Mr. Irwin told Hugh Davies, who was then the director of the Museum of Contemporary Art San Diego, in a 2007 interview: “The pure subject of art is human perception. Once you take that position, it changes all the rules of the game for what you do and how you do it.”

Robert Walter Irwin was born on Sept. 12, 1928, in Long Beach, Calif., to Overton and Goldie (Anderberg) Irwin. His father ran a contracting business that thrived in the 1920s but failed during the Depression, when Irwin was growing up. Overton later worked for the local department of water and power.

Bob Irwin grew up in the Baldwin Hills area of Los Angeles. By the time he graduated from Dorsey High School, some early interests, like drawing, hot rods and betting on the horses at the Hollywood Park racetrack, were clear. (When art sales weren’t paying the bills, wagers at the track helped.)

After joining the Army and spending time stationed in Europe, Mr. Irwin returned to Los Angeles and attended a string of art schools. But he found himself bored by the coursework. More central to his development, he said, was another experience in the mid-1950s: eight months he spent alone in a cabin on Ibiza — then little more than a desolate island off the coast of Spain — without talking to anyone.

It was during this period of thinking, and emptying his mind of thoughts, that Mr. Irwin discovered both excruciating boredom and total serenity. And it was this kind of intensity that, once he was back in Los Angeles, earned this relatively untested artist a spot in 1958 at the fabled Ferus Gallery, which helped launch local artists like Ed Ruscha and Billy Al Bengston, as well as the New York superstar Andy Warhol.

Mr. Irwin’s style in the late 1950s consisted of large, second-generation Abstract Expressionist paintings that were inspired, he admitted, by Mr. Bengston. That would soon change: Mr. Irwin’s development in the 1960s, which he often described as a Zen-like emptying out of the painting plane, culminated in his abandonment of picture making altogether.

The first step, he often said, was his line paintings, an attempt to reduce “incidental distractions” by making an increasingly limited number of gestures across a canvas. Then came the so-called dot paintings, which had even less of an identifiable subject, as painted dots were dispersed across the canvas like something gaseous in nature.

Then he started making curved disks: three-dimensional paintings made of aluminum or acrylic that seem to float ethereally against the wall.

In 1969, the Los Angeles County Museum of Art invited Mr. Irwin to contribute to its Art and Technology program, which paired artists and scientists. Mr. Irwin asked Dr. Edward Wortz of the Garrett Aerospace Corporation and James Turrell, a fellow Light and Space artist, to be his collaborators. They conducted sensory deprivation experiments at the University of California, Los Angeles, and took copious notes.

But before any artwork was realized, Mr. Turrell withdrew from the project, and he and Mr. Irwin famously stopped speaking to each other for decades. They also made great efforts in interviews to distinguish one man’s work from the other’s.

“The difference between me and Turrell leaving a room empty is that Turrell would make you take your shoes off — it becomes a ritual for him,” Mr. Irwin said in a 2007 interview.

Mr. Turrell said in an unpublished interview a few years later, “I think that’s fair,” referring to his travels to Japan, where “it wasn’t a big thing to take off your shoes there.”

“Also, if you have a ranch,” he continued, “taking your dirty bits off in the anteroom or mud room, you can really keep the house cleaner. It has helpful connotations, other than just the visual.”

The two artists eventually did resume speaking. “What happened was my fault,” Mr. Turrell said. “There were jealousies on my part, being the younger artist. He had been showing longer and had his gallery and exhibitions already. I felt that my ideas were as good ideas as his, but I did not have the same ease of showing.”

Indeed, museum shows — even those focusing on near-empty rooms — came early to Mr. Irwin, and he never returned to painting.

In 1970, he reworked a rather homely leftover space at the Museum of Modern Art in New York through a few minimal gestures, including revamping the lighting fixtures and hanging a scrim from the ceiling.

In 1975, at the Museum of Contemporary Art in Chicago, he transformed an empty room by running wide black tape across the floor to complete a rectangle formed by the black border at the bottom of the room’s other walls. In 1980, he replaced the facade of a gallery in Venice, Calif., with a white scrim, in effect exhibiting the gallery rather than anything inside it.

Despite some obvious challenges, museums have managed to collect Mr. Irwin’s work. Most notably the Museum of Contemporary Art San Diego, which mounted a major show of his work in 2007, has become home to an unrivaled trove of some 55 works, including dozens of drawings as well as 10 installations. One is built into the very museum walls of the museum’s La Jolla branch: Called 1°2°3°4°, it consists of three rectangles that Mr. Irwin cut into the museum’s tinted windows facing the Pacific Ocean, bringing the sea breeze, smell and light directly into the museum as part of the experience.

In 2020, when he was 91, Mr. Irwin staged an exhibition under the title “Unlights” at Pace Gallery in Manhattan, a show he called his “swan song.” It featured eight new sculptural works, composed of six-foot fluorescent lights, installed on a wall in vertical rows and wrapped in layers of theatrical gels. “The results are ravishingly gorgeous, and compoundingly confounding,” Mr. Weschler wrote in The New York Times.

Mr. Irwin also tried his hand at high-profile public projects, designing airports, parks and city monuments. Most went unrealized for budget or planning reasons, but he did complete a few large-scale works.

After 15 years and multiple iterations, he transformed the site of an abandoned Army hospital on the outskirts of Marfa, Texas, owned by the Chinati Foundation, into a walk-in installation defined by rows of windows and series of scrims. It opened in 2016. A 2023 documentary film, “Robert Irwin: A Desert of Pure Feeling,” using time-lapse video of the construction, presents the project as the culmination of his experimentation with light.

He is survived by his wife, Adele (Feinstein) Irwin; their daughter, Anna Grace Irwin; and a sister, Patricia Keenan.

Mr. Irwin’s Getty Center garden is now a popular tourist attraction, to the point that some fans say that it eclipses the art collection inside. Not one to take a garden for granted, Mr. Irwin arranged the plants in order of increasing complexity, with an eye to colors as well. He called his work “a sculpture in the form of a garden aspiring to be art.”

Alex Traub contributed reporting.