Daylight.

Interiors I like most are rooms with lots of light, in terms of huge windows letting daylight inside as well as light colors and mirrors, spreading it even more. It is nice when daylight steps inside our homes. Leading to an up-regulation in hormone production it has indeed a positive impact on our health.
Did you know lightness rises the body's level of seratonin which has a positive impact on our mood? Another benefit of sunlight is its ability to boost the body’s vitamin D supply, which indeed is highly protective. It plays an important role in calcium metabolism and helps sustaining a strong immune system. Doesn't that sound great?
However reality shows most of us don't really spend much time outside. Think about your own habits: when you get your groceries, do you walk or take the car? How about getting to work, wouldn't it be possible to replace the subway by bike? I have my times when I decide from now on to use my bike only, for everything! Such overall changes hardly work out well, and still in some cases it is also unavoidable to do so.

Being aware of the benefits is a first step though. Going shades-free in the daylight, even for just 10–15 minutes, could confer significant health benefits and cheer you up. That is something that could possible work, right?