Melatonin is naturally released through the pituitary gland and is controlled by the circadian function. Circadia function is less well understood and it was not until 2001 that Scientists discovered the connection between the ganglion retinal cells (3rd photoreceptor) in us and circadian function.
What does this mean - light triggers circadian function. When you wake in the morning there is more blue light and this will activate the pituitary gland to release more cortisol. Your energy levels will be higher. Conversely more red in the light will activate your 3rd photoreceptor and trigger more seratonin/melatonin to be released making you more tired and prepared for sleep.
Taking an over the counter melatonin product goes through your liver and is like taking oral version of hunman growth hormone. Any benefits are destroyed by the acid and liver and the efficacy is non existent. Sorry but this seems to be another get rich scheme by drug companies and we don't know the exert of the side effects. Further these products are not regulated by the FDA and you have no idea what you are infact ingesting.