An hour or two on the floor of Janet Saad-Cook's downtown studio is an unusual and gratifying way to celebrate the approaching winter solstice.

Every clear day between 11 and 2, the sun beams into the artist's two south windows in the LeDroit building, bounces off what looks like a heap of trashed metallic paper on the floor, and sets the crumbling walls and ceiling ablaze with arcs, slashes and bouquets of colored light. The effect is soothing and beautiful.

Saad-Cook calls this installation a "Sun Drawing," and indeed it requires the sun to bring it to life. "But this is not just an ambient glow," she says. The constantly changing patterns and colors on the walls -- some in the shape of sweeping golden brush strokes -- reflect the constant movement of the sun, but they don't just happen. They have been carefully orchestrated by the placement of reflective material on the floor: golden paper, sheets of a bronze-finished material called Kapton (used in space flight as insulation) and wads of iridescent plastic film that breaks up white light like a prism, dappling the wall with every color of the rainbow.

Still experimenting with the reflective and refractive qualities of various materials, Saad-Cook is hoping for a commission to make a larger, more permanent effort possible. Meanwhile, this is the first public appearance of her work since her show at Gallery 10 two years ago, after which vandals ravaged her Hanover Place storage space and destroyed all of her work.

Her new "Sun Drawing" is well worth the fun of seeing for those who don't mind a precarious climb to room 212 on the second floor, 810 F St. NW, opposite the National Portrait Gallery. Hours, today and next Saturday, are 11 to 2 or by appointment. Be sure the sun is shining when you go.

Saad-Cook has also documented several earlier "sun drawings" with Cibachrome color prints which can be seen at the home of private Bethesda dealer Marsha Mateyka, 6407 Marjory Lane, today and next Saturday from 1 to 5, other days by appointment (phone 229-1970). David Hockney Prints

Though there are waiting lists in London and New York for David Hockney's art, a lode of his prints -- many of them rare, most of them artist's proofs and all of them for sale--has just turned up at the new David Adamson Gallery, 406 Seventh St. The show, which opens today, comes from a secret but impeccable hoard close to the artist.

The 17 etchings and lithographs (plus the complete Cavafy portfolio) span 20 years of Hockney's endlessly inventive art, from etchings made while he was a penniless student at London's Royal College of Art (including the 1962 "Rumpelstiltskin" and "Acrobat" etchings) to images from his more recent "Blue Guitar Series," including the witty takeoff titled, "What is this Picasso?"

But the most memorable images are the portraits of Hockney's friends -- Henry Geldzahler; "Mo," and his longtime printer, Maurice Payne -- whom he has often captured with Ingres-like mastery and clarity. All-male love -- and loneliness -- are also recurrent themes, powerfully dealt with in the Cavafy Portfolio (ask to see it), based on the poems of yearning by the Greek writer C. P. Cavafy. It is typical of Hockney that his feelings about all his subjects are very close at hand.

This is by no means a comprehensive show of work by England's brightest art star, now 45, but it is a treat in a city where Hockney has not been seen at all since his Hirshhorn show in 1979, nor since 1975 in a commercial gallery. Dealer David Adamson -- not to be confused with Adams-Davidson Gallery in Georgetown -- is also a master printer who keeps a lithographic press nearby, and has just published a new print by Gene Davis, which is on view along with a hand-tinted street scene by Kevin MacDonald.

Also available are four wonderful Hockney books, including the latest, featuring the artist's recent foray into photography. Hours are Tuesdays through Saturdays, 10 to 5:30, through January. Beyond Boxing

Mickelson Gallery, 707 G St. NW, is celebrating "Bellows: The Boxing Pictures" at the National Gallery, with a Bellows show of its own -- this one for sale.

Consisting of a few dozen lithographs and three surprising pastoral landscape paintings, the show makes this important point: There's a lot more to George Bellows (1882-1925) than his boxing pictures, though fine examples are included in Mickelson's show.

The Ashcan School master created nearly 200 lithographic images during his short lifetime (he died at 42), and the range of subjects was vast and varied. There were sunny lawn-tennis games, weddings, family portraits, as well as the more somber views of revivalist preachers trying to rouse the masses. Mood and style were similarly vast, from a cartoony view of a businessmen's exercise class at the YMCA, to the dark, scary, Goya-like "Dance in a Madhouse."

Bellows was a major American artist -- the first ever honored at the National Gallery with a one-man show, back in the late '50s. Before that -- and since -- his reputation seems not to have caught up with his talent. His views of the artist's life in New York are particularly appealing. The show continues through Jan. 17, and is open Mondays through Fridays, 9:30 to 5; Saturdays to 4. Painting in the '80s

Jack Perlmutter's 14th annual open-studio days -- the oldest in town -- take place today and tomorrow, 10 to 5, at 2511 Cliffbourne Place NW. New paintings as well as prints will be on sale. Each day at 2, the witty, former Corcoran lithography professor will talk on "Painting in the '80s: What to Expect and How to Look."