Here's an interesting article on light and health the Sydney Morning Herald last Sunday 21st June 2015. Six Ways Sleep Deprivation Can Damage Your Life . The article is at an introductory level and doesn't include any mention of melatonin - still it is worth a read.  The graph showing the increase of incidents related to sleep disorders is interesting - it's  steady increase.  And the link to Altzheimers is also important for investigation.