You need sunlight in order to be human - sunlight:

for a positive mood - serotonin produced helps with depression and anxiety.

improved recovery time - patient rooms with natural light recover more quickly.

helps you get better sleep - melatonin regulates your sleep and depth of sleeping.

gives bone health - Vitamin D helps fight osteoporosis.

helps productive work - sunlight in work spaces shows improved focus.

gives stress relief - DHEA the stress relief hormone counteracts the effects of cortisol.