Contemporary light planning is concerned not only with adequate daylight levels in interiors, but also with the physiological and psychological effects of light. The standards define the relationship between inside and outside, but they don’t define the quantity or even the quality of daylight in interiors. Yet the negative effects on our bodies and minds of too little daylight have long been a proven scientific fact. In addition it has been shown that light influences our performance, can help cure winter depression (also called seasonal affective disorder – SAD), is a catalyst for vitamin D synthesis, and affects the composition of the blood.