What follows you around nearly everywhere but you never notice?

It may sound like a joke from a Christmas cracker but the answer is, of course, your shadow. Not only shadows of the human figure, but also shadows of trees, buildings and everyday objects surround us all the time — though we barely notice them.

The National Art Center, Tokyo’s current exhibition, simply titled “Shadows,” aims to encourage museum-goers to be more aware of shadows in art, and perhaps also in life, by exploring the work of 100 artists from different periods and cultures working in various media.

Having no collection of its own, The National Art Center’s exhibition features over 170 pieces, including painting, lithography and photography, selected from the more than 33,300 items in the combined collections of Japan’s other four national art museums — The National Museum of Modern Art, Tokyo; The National Museum of Modern Art, Kyoto; The National Museum of Western Art, Tokyo; and The National Museum of Art, Osaka.

The exhibition starts by differentiating between “shadows” per se and “shade,” two terms often used interchangeably. Strictly speaking, shadow is caused by the obstruction of light by an object and therefore usually has a distinct shape, while shade is caused by a lack of sunlight (in corners, recesses, covered areas etc.).

So far so good, but things get a bit stretched when the exhibition extends the concept to include reflections, which in the Japanese language shares the same word as shadow — “kage.” While this may seem strange to the rest of us, the broken zig-zag reflections of boats in the water in a hazy photograph by Alvin Langdon Coburn actually do resemble shadows, even if only because they are too dark to make out. In comparison, the reflections of trees in Kaii Higashiyama’s “Reflected Images” (1962) appear unnaturally flat and altogether too clear. It seems likely the artist painted an idealized concept of reflections — his pet theme — rather than a study from life.

Figurative art is well represented, starting with a selection of portraits that utilize shadow and shading to either emphasize facial features and the human form, such as those by early 20th-century Japanese artists Narashige Koide and Ryusei Kishida, or slightly obscure the face, as do the works of French Impressionist Henri Jean Guillaume Martin and Japanese painter Kunitaro Suda.

More interesting perhaps are the works, such as a few by Eugene Delacroix and Francisco Goya, that go beyond this kind of 3-D rendering to explore the more dramatic possibilities of shadows.

A particularly strong work by Jusepe de Ribera uses deep dark areas to create mood and atmosphere. Unfortunately, though, there are no works by this artist’s early mentor, Caravaggio, the master of chiaroscuro.

As can be the way with exhibitions put together from existing collections (even a formidable one such as this) rather than from artworks sourced for the occasion, much of importance has not been included. It’s a drawback that is evident again when a handful of works inspired by the Surrealists (particularly Salvador Dali), remind us of the conspicuous absence of not only the specific artists behind the inspiration, but also of others, such as Giorgio De Chirico, who, of all this group, fully grasped the potential for enigma that shadows offered.

In this respect, “Shadows” can be an uneven affair, but there is still a lot to enjoy. Landscape art is represented by a dozen or so works, one of the most memorable being Indo Matate’s “Cherry Blossoms at Night,” which uses shadows creatively to heighten the atmosphere. In this 1897 painting, the trees are lit not by the electric lights of today but by small fires — the red from the flames adding a hint of color to the silhouettes of the figures enjoying the night view.

In “A Road Through an Oak Wood” (late 17th century) by Dutch artist Jacob van Ruysdael, the center of interest is not the road but the ray of light that cuts through an opening in the dark cluster of trees and spills onto it. At the other extreme, the open road in Monet’s “Road of la Roche-Guyon” (1880) is largely sunlit, overlaid in places with his trademark blue shadows.

There is also an interesting selection of black-and-white photography, a medium where strong shadows come into their element. Here, the simple and powerful composition of Lennart Olson’s “Tjorn Bridge” (1962) may likely catch your eye from across the room, the bridge reduced to a near-silhouette dominating the frame. Elsewhere, strong, graphic patterns of shadows that fall across staircases, buildings and furniture are central to images by Paul Strand, Alexander Rodchenko and others.

The exhibition winds down with explorations of shadows in modern and conceptual art, with even Andy Warhol’s “Marilyn” (1967) making an appearance. Jiro Takamatsu’s installation “Shadows” — a white circular screen — takes up almost the entire width of one room. On the screen can be seen different intensities of light emphasizing the shadows of several human figures.

Marcel Duchamp is represented with four of his “readymades” — everyday shop-bought objects turned into art. Two of these are hung so that while their shadows are easily seen, the original objects are kept out of the viewers direct line of vision. One of Duchamp’s fascinations with shadows was their transformative potential — if the shape of a hat stand, for example, resembles that of a spider, the ambiguity is even more pronounced with the object’s shadow.

“Shadows: Works from the National Museums of Art” at The National Art Center, Tokyo runs till Oct. 18; admission ¥1,000; open 10 a.m.-6 p.m. (Fri. till 8 p.m.). For more information, visit www.nact.jp/english/exhibitions/2010/ shadows.html