John Ott doesn't take the sun lightly. At 77, he sunbathes "fully nude" an hour each day. To increase exposure, he lights his Sarasota home with special florescent lamps that mimic the spectrum of natural sunshine. And he has installed a special plastic in his windows that transmits the ultraviolet rays regular glass screens out.

At a time when medical science frowns on sunshine, linking overexposure to skin cancer, Ott basks in it. Robust and ruggedly handsome, he champions the notion that sunlight can cure much of what ails mankind.

"Twenty years ago I came down here from Chicago on crutches because my arthritis was so bad -- but the sun cured that," says Ott, who quit banking when he was 39 to pursue his boyhood hobby of time-lapse photography. While his films of blossoming plants were soon attracting Hollywood producers (he shot the geraniums that Streisand serenaded in "On a Clear Day . . ."), Ott's experiments with lighting techniques gradually overshadowed his photography.

Once, while filming a Disney segment, he accidentally discovered that "cool-white" florescent light manipulated pumpkin plants to grow mostly male blossoms and "daylight" florescence produced mainly females. He convinced Loyola University of Chicago to replicate the experiment higher on the evolutionary ladder, substituting guppies for sprouts. Results were similar. With additional testing, he developed another lighting formula that the chinchilla industry still uses to breed five times more females than males.

Convinced that natural light is a blessing and normal artificial lighting causes "malillumination," Ott has dabbled for years pioneering dramatic -- if not always scientifically sound -- research on the influences of light on health. One study showed that full-spectrum radiation-shielded lighting (simulating natural sunlight) in two windowless Florida classrooms calmed hyperactivity, improved learning disabilities and reduced tooth decay.

He currently promotes using light treatments to combat the "clumping of red blood cells" caused, he contends, by magnetized fields emitted from video display terminals. The author of three books who has given more than 4,000 lectures complains that "the greatest problem is getting people to listen."

But, lately, an increasing number of researchers and physicians have set out to prove that such light theories are far from lightweight. This new breed of scientific sun worshipers has revived an ancient and controversial science that has been all but ignored in the 20th century -- photomedicine.

Its potential? Depends on whom you ask. But a cross section of those investigating sunlight say today's proven attributes -- treating psoriasis and jaundice and the manufacture of Vitamin D, among them -- only "scratch the surface." Tomorrow's findings could provide insights and treatments for sleep disorders, hyperactivity, allergies, endocrine diseases and psychological problems.

* "The sun is taking a bum rap," says Dr. Zane R. Kime, an Auburn, Calif., physician who in 1980 published Sunlight Could Save Your Life (World Health Publications, $11.95). In it, Kime prescribed "sunlight therapy" for health and psychological benefits that include lowering high blood pressure, blood sugar and cholesterol levels, increasing resistance to infection and preventing chronic diseases. Critics suggested Kime was practicing medicine as if the sun were the center of his universe. They were correct.

Kime, a conscientious sun-seeker who has installed full-spectrum lighting to simulate daylight in his office, insists, "The sun has always been with us, it is a natural part of our lives. It is only lately that we have been having all of these problems.

"We spend most of our days indoors and the lighting is totally unnatural and it really is affecting our health, our hormones and our whole health picture. We are really performing a giant experiment on mankind . . ."

Five years ago, Dr. Norman E. Rosenthal, psychiatrist and director of the Seasonality Program at the National Institute of Mental Health, embarked on a study of the psychological effects of manipulating light intake. By exposing patients to high levels of sunlight-simulating, "natural wavelength" light, Rosenthal and his colleagues found that the symptoms of seasonal affective disorder (SAD) -- winter's chronic funk of fatigue, oversleeping, overeating, craving for carbohydrates, sadness and depression -- are reversed.

"This last winter we looked at normal individuals who didn't show any symptoms of SAD," says Rosenthal. "A small number of people who had a completely clean bill of emotional health didn't show any improvement with the lights."

Rosenthal theorizes that "February blahs" or "gloomy moods on rainy days" are real conditions that affect most of the population that falls somewhere between SAD sufferers and the unafflicted. That his NIMH colleagues have been "pilfering" his experimental lights and "putting them in their offices," he adds, is further evidence that the light regimen can help.

"I don't want to sound like we have a snake oil to cure all ills . . . ," cautions Rosenthal. "But I think now that we find these higher intensities are having diverse effects on the brain, the whole area of light research has regenerated as respectable."

As director of the Vitamin D and Bone Metabolism Laboratory at Tufts University's Human Nutrition Research Center, Dr. Michael Holick has conducted 10 years of clinical investigations of Vitamin D. His latest research indicates "a hidden epidemic" of Vitamin D deficiency in America's aging population.

"We're now finding that the elderly are prone to Vitamin D deficiency," says Holick, explaining that the lack of Vitamin D can cause osteoporosis, a condition in which bone mass and calcium are decreased and bones become fragile and prone to fractures.

"We are now encouraging people to really think about the beneficial effects of sunlight," says Holick, who also uses full-spectrum lighting in his office. "We are now recommending to the elderly that if they go outdoors for 10 or 15 minutes in the summertime, two or three days a week, they can make adequate amounts of Vitamin D."

At the SERA Corp. in Vienna, Va., Dr. Russell Jaffe, a physician and biochemist, uses diachromatic colored lights as part of a treatment for chronic and severe allergies and immune system disorders. Called the ELISA/ACT Test, the treatment can be traced to turn-of-the-century light and color therapy and, says Jaffe, is practiced today in Sweden, Australia, Japan and Israel.

"It doesn't take much of a great intellectual leap to understand we are physical, chemical, electrical and magnetic -- and we may be more than that," says Jaffe. "The art is knowing what to apply when, where and how.

"In our culture, medically we tend to be chemically dominant. The first thought of most physicians is to reach for a pharmaceutical for most patients' needs. And that is appropriate in many situations. In other cases, nonchemical means may be more appropriate."

Jaffe says his typical patients suffer chronically persistent symptoms such as inflammatory bowel disease, joint aches and pains, chronic flu-like symptoms, too many colds, recurrent infections, migraine headaches or sleep disorders that don't yield to usual therapy.

"We use a particular kind of color light . . . that generates a specific frequency," says Jaffe, adding that when shown on the skin, "at the right time for the right purpose, it can actually have a biological effect. What we can certainly demonstrate clinically is a beneficial effect."

Ben Lust, owner of Ben Lust Theater Supply in North Bethesda, Md., says Jaffe's light therapy has increased his sales of diachromatic bulbs by 200 percent. "I was skeptical," says Lust. "These are beautiful bulbs . . . Until I met the doctor, I had them strictly for decorative reasons . . . nightclubs or Christmas trees. But in the past year, I've had 40 or 50 people come in here and thank me just for selling them these bulbs."

Dr. Richard Wurtman, director of research at the MIT's Laboratory of Neuroendocrine Regulation, likes to talk about sunlight as a drug.

"Turning on and turning off the light is like administering a drug," says Wurtman, a light research pioneer who organized the first conference on the medical and biological effects of light in 1984. "But it is a very nice drug. Like a kind of vitamin, it is something one should get leading a normal life, but it can also be applied for particular uses . . .

"Each year that passes, it is safe to say we discover previously unknown benefits of light," says Wurtman, who for 10 years has installed a simulated natural light in his office called Vita-Lite, developed by Duro-Test Corp. of North Bergen, N.J., and used in most light therapy research.

Listed (though not approved) as a medical device with the Food and Drug Administration, Vita-Lite simulates a full visible spectrum "sun-plus-sky" light and balances ultraviolet rays that otherwise are harmful, says Philip Hughes, director of environmental photobiology at Duro-Test and a former staff scientist at MIT.

"It has been marketed 15 years, at first for improved color and enhancement of the environment, and later as a general purpose simulator of natural outdoor light," says Hughes. "But as scientists started to look at the benefits of natural light, they came to us for use in their studies to simulate natural light indoors."

The result, says Hughes, was a 2-by-4-foot florescent fixture designed to house six to eight Vita-Lite 40 watt lamps, with special reflectors and a special lens to prevent distortion. Patients in studies such as Rosenthal and Holick's typically sit three feet away for varied lengths of time.

When Hughes addresses the Second International Conference on the Earth Sheltered Environment at the University of Minnesota in June, he intends to emphasize that "the 20th century has seen a shift from rural country living where 75 percent of the population worked outdoors to urban/suburban living where most people work indoors away from natural light."

Says Wurtman: "We should reconsider the intensity of light under which we work. The availability of light outside is 300 or 400 foot candles. Most of us work under no more than 80 or 90 foot candles. I can't prove to you that increasing those intensities will improve our lives. That's for future research."