In the bedroom of the future, there won't be harsh buzzers or rude alarms or even radios set to beautiful music to wake people up in the morning. Instead, there will be "photic alarms" -- devices that mirror Nature's own most powerful waking mechanism: the dawn. Over a couple of hours, this computerized illumination system will increase the light at your pillow from dusk to sunrise. Subtle signals from this artificial dawn penetrate your eyelids and are picked up by the nervous system. This triggers a number of important physiological events and results in wakening. And for the maximum benefit, these photic alarms to herald dawn's early light will always be set for spring. "The spring equinox is an important moment physiologically," says Michael Terman, who is experimenting with a photic alarm device in his work as director of the Light Therapy unit at the New York State Psychiatric Institute in New York City. "It's the crossover point at which the population as a whole moves from the time people feel the worst to the time they feel the best." Scientists are now confirming what poets have been saying for centuries. To everything there is a season, and spring -- for most people -- is the season of high energy, productivity and bright moods. Like all living organisms, humans follow cycles -- daily, monthly, seasonal and annual. And despite the evolution of modern folk to climate-controlled environments, seasonal cues may still affect everything from job performance to sex lives. Studies show that the highest rates of conception take place in spring and male sex hormones peak in the fall. On the other hand, most deaths occur in January and February, and a quarter of the population may suffer winter blues that spontaneously disappears in spring. Most people say their peak positive response occurs in April, May and June. "When spring comes, most of us are more energetic, active and sexually interested," says Dr. Norman Rosenthal, director of seasonal studies at the National Institute of Mental Health. "We feel a certain zippiness, a spring fever, if you like." In the past decade, researchers have gained new insights on how the seasons affect mood and behavior. Specialists in this field, called chronobiology, have found that variations in the day/night cycle and the seasons result in a wide range of physiological and psychological behaviors that are a normal part of experience. Recent research, for example, is showing seasonal changes in sleep length, level of daytime energy, food selection and weight gain. These changes vary from person to person and may alter with age, scientists say. But they appear to be triggered by the same cues that prompt animals to mate or hibernate -- the changing length of days. The body's internal clock, which controls body temperature, hormone secretion and sleep patterns, shifts ahead or is delayed when stimulated by or deprived of light. Winter Blues In winter months, as the sunrise gets later and the nights get longer, a number of important physiological events begin to slip as well, researchers explain. One theory involves the secretion of the light-sensitive hormone melatonin, which is thought to be a physiological signal to the brain for darkness. Blood levels of melatonin are rapidly reduced by light exposure. As sunrise comes later in winter, the morning wake-up signal is delayed and melatonin secretion is out of synch with the sleep cycle. These changes are thought to have a depressing effect. This may help account for a type of "winter blues" experienced by an estimated 25 percent of the population in the middle to northern latitudes of the United States. The "blues" are so severe in some people that they are unable to function during certain periods of the year. This form of depression, called seasonal affective disorder (SAD), was identified in the early 1980s at the National Institute of Mental Health. Since then, a growing number of psychologists and psychiatrists are reexamining patients who seem to have the winter blues. "People suffering from seasonal affective disorder (SAD) often feel chronically depressed and fatigued and want to withdraw from the world and to avoid social contacts," says Terman, a physiology psychologist. "They may increase their sleep by as much as four hours or more per day, have greatly increased appetite and gain a substantial amount of weight." Yet for many SAD sufferers, spring brings on a spontaneous remission without any active intervention. People who are distraught three to four months beforehand reach their ideal state in early spring to late summer. To many researchers, sunlight, particularly the timing of dawn, appears to be responsible for this dramatic change. For that reason, a growing number of specialists are treating SAD patients with artificial exposure to intense light. In the last five years, numerous studies have shown encouraging results from using light to treat patients with SAD. Timing of light therapy also appears to be important. Terman's latest analysis of studies on 332 patients at 14 medical centers shows that morning is the best time for light therapy. "My current belief is that the gradual dawn of light serves as nature's alarm clock, and that the brain is hungry for early morning light," Terman says. "This is why so many people have trouble awakening. They are denying themselves the needed light by pulling down windowshades and sleeping in totally darkened rooms. "The majority of people have inadequate exposure to the dawn signal. It's an aspect of the environment that modern people have shut out of their lives." For those who can't get enough of Nature's light, or for whom spring doesn't come soon enough, therapeutic lighting may be useful. In some studies, people who in winter months sleep two to three hours longer than in summer and do not feel awake until around midday are able to wake normally when exposed to artifical light that precisely simulates the behavior of the spring sunrise. Therapeutic lights might also help people who must work at night and sleep by day, as well as those who need to change time zones.Cookie Cravings Light exposure may also help with two other cyclic disorders that appear worse in the winter: carbohydrate-craving obesity (CCO) and premenstrual syndrome (PMS), according to Dr. Richard J. Wurtman and Judith J. Wurtman in the January issue of Scientific American. The earth's daily dark-light cycle appears to be the basis for the cyclic patterns of all three disorders, they write of SAD, CCO and PMS. These disorders appear to be affected by biochemical disturbances in two different biological systems. One system involves the hormone melatonin, which is responsive to light and affects mood and subjective energy levels. The other, they say, involves the brain chemical serotonin, which regulates a person's appetite for carbohydrate-rich foods. Carbohydrate cravers experience daily eating peaks, typically at 4 p.m. and 10 p.m., as well asseasonal peaks, says Dr. Richard Wurtman, director of the Massachusetts Institute of Technology's Clinical Research Center. "In winter there's a propensity to overeat carbohydrates . . . {which} have a special effect on chemicals of the brain that make us feel better. At a time when we don't feel good, we can make ourselves feel better with carbohydrate snacks." The theory is that carbohydrates such as pasta, cereals and breads stimulate the brain chemical serotonin, which in turn produces a mood of well-being. Carbohydrate craving lessens in spring because "a bad thing, winter, went away," he says. Winter blues and weight gain, moreover, often go hand in hand. "Most people have a mild case of SAD," says Wurtman. "In spring we are full of energy and creativity, our craving for carbohydrates lessens and we tend to lose the weight we gained over the winter." As for PMS, some people report increasing severity of symptoms in winter, says David Rubinow, NIMH clinical director. But as a general rule, it is not a frequent observation. Spring is not universally embraced. A minority of people are unable to make this high-energy shift to spring, and the results can be tragic. "Suicide is common in the late spring and early summer," notes Rosenthal of NIMH. Typically, all of these positive shifts in mood, energy level, diet and sexual interest occur in parallel. But if someone can't make these shifts, or can make some but not all, the result can be an agitated, depressed state. "That kind of depression is more dangerous in terms of suicide than is the depression of SAD," says Rosenthal. "It's like the horse pulling ahead, but the cart doesn't follow. The reins snap."Seasonal Rhythms Before you decide to search for a land of perpetual spring, scientists are quick to point out that seasonal shifts are vital to well-being. In fact, when there are no seasons, the effect on human health can be dramatic. "Our big concern is with space travel," says Murray Hamlet, director of the Cold Research Division at the Army Research Institute of Environmental Medicine in Natick, Mass. "The conjecture is that without experiencing seasons, you would free-run the pineal gland," which is thought to control the secretions of hormones such as melatonin. "This would interfere with the normal circadian cycle, and you'd never get any restful sleep. You'd be a chronic isomniac." To guard against this in space, artificial lights will likely be used to simulate a 24-hour day as well as the seasons of the year. Hamlet plans to experiment with the effects of artificial light in a season-free environment by doing studies on people who winter over at South Pole Station. "There, you go for 10 months without sun," he says. "You see a lot of depression. You also see something we call Big Eye. That's the buggy sort of gaze you get after going months without sun. It's a 12-foot stare in a 10-foot room." But light is not the only cyclic force that acts upon human behavior and physiology. Seasonal rhythms related to gravitational fields in the moon or electromagnetic fields, as well as to changes in climate, also exert influence over basic body functions such as reproduction and menstruation. Scientists know that these forces act on animals, such as migrating birds. It's not unreasonable, they say, to think that they affect people, too. But while "the seasonal behavior of most animals is taken for granted," writes Kenneth Jon Rose in "The Body in Time," the "evidence that human physiology follows the seasons is far more enigmatic." Part of the problem lies in the fact that most people today live in the city. It is an environment ruled more by the clock and central air conditioning and heating than by Mother Nature and any rosy-fingered dawn. Many other factors such as culture, religion, nationality and economy have dominant impacts on human behavior. Yet, despite the difficulty in separating the influences of artificial environments from raw human physiology, scientists have isolated some fascinating seasonal patterns. Rose, who teaches physiology at New York University, reports these findings among the most basic human variations: Death occurs most often in winter -- even in Hawaii. Conception rates peak in the spring, with a lower peak in the fall -- and the highest rates of birth occur around the winter with a lower peak occurring in the summer. Male testosterone levels are highest in October and lowest around May -- but sperm count is highest in spring. Birth weights of babies delivered in the summer and autumn tend to be slightly greater on the average than those delivered during other seasons of the year. Just why these seasonal variations occur is not known. Scientists suspect that some rhythms of human reproduction stem from early survival strategies of primitive societies. Other changes may have to do with cultural patterns and economic shifts. Many illnesses also follow a marked seasonal pattern, says epidemiologist Steve Teutsch of the Centers for Disease Control in Atlanta. But the seasonality is attributed more to social conditions and disease carriers, he says, than to the changes in the seasons themselves. "Encephalitis is carried by mosquitoes, so you see it in the summer," he says. "Head lice tend to occur right after school starts." "Influenza rates are higher in winter when viruses are more likely to be picked up by people in crowded environments," says Dennis M. Driscoll, associate professor of meteorology at Texas A & M University. "But then, rather inexplicably, dental caries maximize in late winter and early spring." Among industrialized countries, seasonal trends in mortality tend to flatten out. Today, scientists emphasize, climate has a much smaller effect on well-being than other factors such as age, wealth and psychological health. "Safe in our crypto-environments, we typically live within a comfort zone that buffers us from the immediate impact of atmospheric vicissitudes," says Driscoll. "The weather component is much less than if we were still living in caves." But despite this protected existence, some scientists speculate that the immune system may still be affected by seasons -- thus helping to explain seasonal trends and disease. The peak in deaths, for example, from cardiovascular disease during the late winter "could be from cold weather or crowding or it could be that our immune system is compromised during that season," says Michael Smolensky, professor of environmental physiology at the University of Texas Health Sciences Center. "It could well be that circadian and circannual rhythms in the occurrence and exacerbation of human disease represent, in part, the contribution of underlying rhythmic changes that became fixed during evolution." Some scientists speculate that modern society's very removal from the natural forces that shaped primitive ancestors is what contributes to seasonal discontent. In the end, they say, the major culprit of high-tech living may be that you lose your daily place in the sun. "Perhaps contemporary life styles increase vulnerability to seasonal depression by diminishing the amount of time we expose ourselve to light," write MIT's Richard and Judith Wurtman. "Perhaps much as office workers join health clubs to compensate for the lack of exercise, people with indoor jobs need to arrange for adequate exposure to light." The following groups can provide information on seasonal affective disorder: National Organization for Seasonal Affective Disorder (NO SAD), P.O. Box 40133. Washington, D.C. 20016; SAD National Hotline of the Light Therapy Unit at New York State Psychiatric Institute at Columbia Presbyterian Medical Center, (212)960-5714.