Hello Amrit,

The neural mechanisms regulating  circadian changes in melatonin secretion are well described. A number of studies suggested a role of the  clock genes  in the control of the phase, and therefore circadian rhythms in melatonin secretion. At the same time, the synthesis of melatonin is inhibited directly by light, and the duration of melatonin release is reported to be related to the length of the dark period. These evidences suggest that there likely multiple mechanisms which drive melatonin secretion in both owls and larks.

Best wishes, Tatyana 

Dear Tatyana, first of all a big thanks for almost answering my question. So, it means that the long exposure to artificial light during night time delay the onset of melatonin secretion in larks (evening chronotypes)? Further, if that is proved, which now I understood it is, then by what period of time this delay onset of melatonin really does set in larks to make them feel sleepy? Is there any specific time/cycle for the same?

Hello Amrit, Yes, it is most likely that two main functions  of the circadian  system, the internal master clock and the environmental entrainment, both regulate each person's physiology and behaviour. With regards to your second question, it is expected that each lark would display own unique phase, which may vary widely within the same individual depending on activity, but where light is the primary "time giver".

Best wishes, Tatyana

Dear Tatyana, got my doubts cleared! heartfelt thanks ! Wish to have more interaction with you in coming days.