 The study is aimed to check a preliminary evidence that bright light may help to lose weight in obese people Thor Helge Bergan, Norvay, 2002, unpublished. Subjects: aged 20-65 y, BMI 30, non-seasonal SPAQ score 8, no seasonal problem, in good general health, with regular sleep from 22:00-1:00 to 6:00-9:00. Study season: November-April. Placebo-controlled, single-blind, crossover. At least 1 mo between two arms; at similar phase of menstrual cycle if present. If could not complete at the first year, the second arm is to be done the next winter. Intervention: Lightbox 4300 lux - during one arm, deactivated ioniser - during another arm sequential alternation upon entering the study for 3 weeks each morning at least 18 days starting between 6:00-9:00. Seating distance from the face to the device is 41 cm, duration - 30 min. Diet: a target amount of kcal per day is calculated based on age, weight and gender WHO, e.g. for a woman 40 y ang 80 kg it is 1502 kcal per day. Food content - is also as recommended by WHO. Food distribution over day - usual for the particular test subject but constant over sessions. Food diary is completed daily and subjects calculate kcal themselves based on a Table of kcal. Outcomes: Weight is measured during a visit to doctor a day before and day after the 3-week session, and also at home every week. Motivation and Expectation are rated by 3-point scales in a Diary, at the beginning of each session. Mood, activity and appetite are self-estimated using a VAS-like 10-points scale every week. At the end of each arm the Easiness of dieting scale and Adverse events are completed. In the diary, there are also columns for sleep on and off times, intervention time, duration and distance, number of kcal. A target number of subjects to complete the study is 40. 