With the arrival of the cold season, besides cold-driven nuisance, some persons experience drawbacks regarding the general state, lack of energy and depression of unknown origin. It was scientifically ascertained that the lack of light favors the production of melatonin by the pineal gland, a hormone inducing sleep. That is why, during the cold seasons when days are shorter and the sunlight is scarce, we often feel sleepy or drowsy. Also, even during spring and summer, if the tendency is to keep most of the time indoors at home or at the office, the effect may be similar, though not as severe. Well, if drowsiness were the only impact generated by season changes, things would be easier to solve (with a little coffee maybe!). The problem is that melatonin secretion is synchronized with the production of a neurotransmitter, serotonin, which is involved in several physiological processes such as temperature, blood-pressure regulation and in neuropsychological functions such as appetite, memory and mood. The two do not work together at the same time. When melatonin is secreted, serotonin production is inhibited. Lack of serotonin causes disorders such as chronic fatigue syndrome and reflects its effects on mood also, triggering depression in some persons. Melatonin is active at night and serotonin is active in the daytime. Also, there is the age factor that contributes to the balance of the two chemicals: the secretion of melatonin decreases with age. There has been established that the link between serotonin and melatonin along with their dependence on the body clock may explain the depression experienced by the people suffering from the disorder called Seasonal Affective Disorder - SAD. Depression, sleep problems, weight gain, anxiety, joint pain, irritability, stress, headaches are some of the symptoms that may appear when we suffer from SAD. The problem is primarily caused by the lack of sunlight. It has been scientifically proven that sunlight favors increase in serotonin levels and favors vitamin D accumulation. Besides having anti-osteoporotic, immunomodulatory, anticarcinogenic, antipsoriatic, antioxidant properties, vitamin D is also a mood-modulator. UV rays exposure favors vitamin D synthesis in the skin. That is why persons who go to tanning salons have noticed mood improvement and keep the habit in order to maintain the state of well-being. However, it is common knowledge that the effects of the UV exposure are not always the most desirable ones. If going to tanning salons becomes a habit, then recurrent, prolonged UV exposure may result in consequences such as premature skin aging and eventually skin cancer. Light therapy represents a way to treat SAD. Light operates on the body in two ways: through skin impact or by entering your eyes. Only UV light has effects on the skin, while the light that has effects by entering your eyes needs not be UV, it just has to be bright. Its energizing effect comes from the fact that it stimulates the production of serotonin. The simplest way to get enough bright light is to spend an hour a day or more outdoors, where the light levels range from 1,000 to 50,000 lux or more, compared to room lighting, which is about 50-200 lux. If your schedule or the weather does not permit it, an alternative is to purchase a light therapy device. For optimum effects, the light source either has to be very bright - 5,000 lux or more - or it has to be in a particular spectrum - around 460 nanometers, which is in the blue range. According to new research, blue range light will provide benefits even if at a dimmer level. Most companies producing light bulbs make full spectrum lights that may successfully replace sunlight. Yet, there are side effects that bright artificial light may induce, namely it may interfere with sleep (especially when exposure is made in the evening hours) or even trigger in some people a mania - condition called bipolar disorder (known as manic depression). The safest remains the natural outdoor light, on condition that UV protection is used.