Sunlight or fake light? We explore how light timing and intensity shape the circadian clock, mood, hormones, fertility, and sleep—and why amplitude is the missing key. Sean Kane shares new research on individual light sensitivity, depression and bipolar patterns, and practical fixes that work.

Sean Cain, PhD is a Matthew Flinders professor of circadian biology at Flinders University, Australia. He has more than 25 year of research into human circadian system and how light affects health.

Join Dr Cain's Adelaide Research project: http://theilluminatestudy.com/
(see below for more study links).

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TIMESTAMPS

2:00 How The Circadian Clock Works
6:30 Ancestral Light Versus Modern Lighting
12:30 Amplitude: The Clock’s Strength Signal
18:00 The Retina’s Hidden Light Sensor
24:30 Melatonin, Blue Light, And Sleep Timing
31:30 Individual Sensitivity To Light
38:30 Light And Mood: Depression And Bipolar
46:00 Risk Taking, Habenula, And Blue Light
53:30 Cortisol, Melatonin, And Rhythms
1:00:00 Skin Light Myths And Real Pathways
1:07:00 Moonlight, Menstrual Cycles, And Fertility
1:15:00 Early Puberty, Seasonality, And Hormones
1:22:00 Longevity, Regularity, And Stable Days

Follow SEAN CAIN
Join Dr Cain's Adelaide Research project: http://theilluminatestudy.com/
Circadian Health Innovations (mi-eye): https://circadianhealthinnovations.com/mieye
X: https://x.com/circadian247

Selected papers
Daylight and depression/insomnia:
https://doi.org/10.1016/j.jad.2021.08.056

Antidepressant increases light sensitivity:
https://doi.org/10.1007/s00213-018-5019-0

Blue light and gambling:
https://doi.org/10.1038/s41598-025-97370-z

Individual differences in light sensitivity:
https://doi.org/10.1073/pnas.1901824116

Light suppresses the human amygdala:
https://doi.org/10.1371/journal.pone.0252350

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