Sufficient natural light is critical to the health and wellbeing of living things. Just look at plants which do not get enough light! Yellow and spindly, they eventually wither and die.
The average human needs about a half hour of full sun each day, about five days per week, to stay healthy. Lack of sunlight can cause vitamin D deficiency, resulting in loss of bone density, and joint problems, as well as depression. In children, a lack of sunlight can lead to painful bone problems, such as rickets.
Other problems associated with lack of light / vitamin D deficiency:
* Myopia
* Heart disease
* Some cancers
* Infections diseases
When designing a room, if natural light is available, take advantage of it! Bringing sunshine in is healthful, and saves energy by reducing the need for electric lights, so let the sun shine in!