References on Light and the Biological Clock

Sleep and Circadian Phase Characteristics of Adolescent and Young Adult Males in a Naturalistic Summertime Condition. Chronobiology International 2000;17(4):489-501
L Laberge, J Carrier, P Lesperance, C Lambert, F Vitaro, RE Tremblay, J Montplaisir

"These results together indicate that adolescents and young adults investigated during summertime showed similar circadian phase characteristics, and that, in these age groups, an evening phase preference is associated with a delayed melatonin secretion pattern and delayed habitual sleep patterns without a decrease in sleep consolidation or vigilance." Full Abstract