For thousands of years one of the most important regulator of life was the sunlight. Basically it defined when we should wake up or go to sleep through a hormone called “melatonin”. From Examine.com:

Melatonin is a neurohormone secreted by the pineal gland in the brain and it is well known for causing and regulating sleep. Light suppresses melatonin synthesis.

Light suppresses melatinon synthesis. Okay. So in the 20-30 years when TV and computers became a thing, our well-precised sleeping machinery increasingly changed and upset our sleeping habits. But some our work and social media with the internet effectively demands our attention and time during the nights and it’s hard to avoid it. That means we are in an endless loop of late night artificial light omitting and lack of natural light during mornings and wake-time due to working in closed offices. That and lack of sunlight during winter era could result seasonal affective disorder, called SAD in some cases, which also called winter depression or seasonal depression.

Fortunately there is a solution called “light-therapy” which somehow tries to regulate back our hormones to a more natural or efficient state. Basically it means that everyday in the same time (preferably after wake-up) getting outside to the nature and swimming in sunlight for 10-30 minutes could help after 1-2 week. However there are places where the sunlight is missing for the winter months, so we need an artificial solution. Hence, the bright-light therapy which means a small light (similarly on the same spectrum as Sun light) omitting device.