The bright summer sun, or other bright light makes your brain cut off the deliverance of melatonin. Melatonin production at night makes us relax and helps us sleep. If released into the system during the day, it becomes a depressant. Being exposed to bright light sources causes you to feel more lively and energetic. Many experience feelings of extreme contentment or vivacity. Tanning is linked to the release of beta-endorphins, which are said to give your system a little pick me up, similar to the feeling after you work out and release beta endorphins into your system.