Perhaps one of the most compelling reasons to drop by the National Gallery of Art this summer is that the landscape painter Sanford Gifford’s paintings, a major retrospective of which opens this Sunday, can only be truly “seen” in person.

While that could be said of many artists, it is particularly true of Gifford, who was a master at depicting light, as it played out against the surface of often gaping, naturalistic vistas, which he painstakingly rendered in glazed layers — a feat that does not lend itself to satisfactory reproduction as prints or in exhibit catalogues.

And if that isn’t incentive enough, “Hudson River School Visions: The Landscapes of Sanford R. Gifford” marks only the third retrospective of the artist’s work in the more than 120 years since his death. Organized in conjunction with the Metropolitan Museum of Art, which Gifford helped found and where it was earlier on display, the exhibit brings together for the first time in some 30 years more than 70 of his cardinal paintings.

Gifford, a leading figure of the Hudson River School — a movement of 19th century artists whose sweepingly majestic portrayals of nature would come to define American landscape painting — was appropriately born in Hudson, N.Y., into a well-to-do family in 1823. He studied to be a portrait painter in New York City but soon returned to his native backdrop of the Catskill Mountains and Berkshire Hills, which would serve as his primary artistic template throughout his life, with the exception of a pair of extended trips abroad.

It was on one of these sojourns in 1855, that he met with John Ruskin and seized on the opportunity to ask the legendary art critic why he so admired the English painter J.M.W. Turner. As subsequent paintings demonstrate, Ruskin’s reply, that Turner “treated his subject as a poet, and not as a topographer,” appeared to have made an impression on Gifford. Henceforth, Gifford would devote himself to his central themes of “unity, consistency, harmony,” whether he turned his attention to a lake at day’s end as he did in the supremely hypnotic “Lake Nemi” in Italy, or to the ruins of the Parthenon as he did in the eponymously named work, which capped his career and is now included in the Corcoran’s permanent collection.

At its core, then, Gifford’s oeuvre is about one man’s visual encounters with landscape. An “inveterate hiker” who regularly covered 40 miles in a day, Gifford repeatedly returned to the same scenes, which he sketched and later revised at whim in his New York studio, said curator Franklin Kelly. He also turned his attention to the world beyond the Hudson milieu with equally incandescent results, as he did during a voyage from Naples, Italy, to Alexandria, Egypt, in the late 1860s. Accordingly, nearly a quarter of the exhibit is represented by Gifford’s often Whistleresque “foreign” landscapes of Venice, Constantinople and Egypt, among others.

But it is a series of paintings depicting a Catskill clove that provide the best example in the exhibit of how Gifford manipulated nature in the process of pursuing artistic harmony.

In his varying interpretations of the scene, pine trees are replaced by birch, Caucasian figures by American Indians, and a jagged mountain vista compressed, then smoothed over by a balming late afternoon sun, which grows more pronounced in subsequent renderings, until it culminates in “A Gorge in the Mountains” as a central, blindingly beautiful, all-encompassing sheen.

To his credit, Gifford never entirely allows the myth of the American landscape to subsume reality. Even in his sunlight-suffused paintings of idyllic mountain and lake retreats, there are what Kelly terms “elegiac” moments. For instance, in “The Wilderness,” an American Indian woman stands at the water’s edge, looking longingly at a Mount Katahdin-like peak in the distance, as if simultaneously contemplating its overarching grandeur, as well as the more personal loss of territory implicit in such a post-Manifest Destiny setting.

After the Civil War death of one brother (Gifford himself would serve with the 7th Regiment of the New York National Guard), the “sunnier” disposition of many of his earlier landscapes begins to make way to more foreboding, roiled elements — expressed in the presence of threatening, fuliginous storm clouds.

Prominent among these is “A Coming Storm,” an autumnal mountain scene whose steely thunderheads overhead presage a soul-rattling outburst. Believed to have been owned by Edwin Booth, brother of Lincoln assassin John Wilkes Booth, the picture is perhaps best summed up by the poet Herman Melville, who wrote of “dim inklings from the shadowy sphere” in one poem on the subject.

Gifford’s light, no matter what mood he portrays, is quite simply divine-like, infusing every element of his paintings. It is light too flawless for words. Light incapable of transmitting damaging ultraviolet rays. Light you would greedily bottle up and take home — if such a thing were only possible.

Given its ineffable qualities, it’s no surprise that the mere act of viewing the landscapes this light infuses can be a protean experience.

On an overcast day, much like the morning of the exhibit’s preview last week, the galleries’ tracklights hit the paintings in such a way that a given room’s illumination appeared to be emanating directly from the canvases — almost as if they were glowing — rather than from above. However, as the sun broke the cloud cover later in the morning, allowing natural light from the skylights to more thoroughly penetrate the rooms, the works themselves seemed to dim slightly.

Gifford is so good at manipulating the atmospherics of a painting through light one can almost feel at times the temperature rise and fall with the color scheme. In “A Winter Twilight,” a trio of men on a frozen river shrink under a looming sky of seamlessly layered reds, yellows, purples and blues, which alternately elicit thrills of warmth and cold in the viewer’s spine.

When it comes to the human forms, which periodically dot his landscapes, Gifford often relays these in a “Where’s Waldo”-like fashion, sometimes as little more than a fleck of paint, which upon closer inspection is gobbled up by the broader canvas. At other times, the figures may be more pronounced but nonetheless seem to remain poignantly aware of man’s ultimate subsidiary status to creation, as does the diminutive hunter staring off into the horizon in Gifford’s early masterpiece, “Mansfield Mountain.”

For all Gifford’s similarity to fellow Hudson River artists, however, there is something uniquely subtle about his work. Just across from the Gifford exhibit, in the National Gallery’s American painting collection, some of his contemporaries’ work — such as that of his idol and Hudson River School founder Thomas Cole — can appear almost cartoonishly simplistic if viewed immediately after the Gifford show.

The same general ideas are there: the centrality of luminous light, the smallness of man juxtaposed against an overwhelmingly magnificent natural stage. But unlike in Gifford, where the canvases exude a sense of refined equipoise, many of these painters’ works suddenly seemed to border on gaudy, greeting-card friendly fare — a fact that can be largely attributed to sequence of encounter. Their relative primativeness was not viscerally apparent until after viewing the Gifford show.

This is not to say that Gifford’s paintings don’t quietly pullulate with the same kind of “wonder at creation,” frequently depicted in many Hudson River School works. They do. It’s just that his technical superiority seems to cast a sophisticated, near universally pleasing patina over whatever he turns his attention to — whether that be palm fronds along the Nile or dozing sailboats on a Hudson River bay. Gifford’s landscapes truly are “bathed in atmospheres of sleep,” as a critic once wrote. Heavenly sleep.

“Hudson River School Visions: The Landscapes of Sanford R. Gifford” runs from June 27 to Sept. 26 at the National Gallery of Art’s West Building.