In this episode of Huberman Lab Essentials, Andrew Huberman explores how various factors like light exposure, temperature, and exercise influence circadian rhythms, mood, and neuroplasticity. He explains that moonlight, candlelight, and fireplaces do not disrupt circadian rhythms due to the sensitivity of melanopsin ganglion cells in the eyes, which are more responsive to blue-yellow contrasts of sunlight. Red light, if too bright, can disrupt sleep, so it should be dim. Sunlight through windows is less effective for setting circadian clocks compared to direct exposure. Huberman also discusses the role of temperature in regulating circadian rhythms, suggesting that cold showers in the morning can help phase advance the circadian clock, making it easier to wake up earlier. Exercise timing can also influence circadian rhythms, with specific windows being optimal for performance and reducing injury risk. He emphasizes the importance of self-experimentation to find what works best for individual circadian and mood regulation. Additionally, Huberman touches on neuroplasticity, explaining how sleep and non-sleep deep rest (NSDR) can enhance learning and memory retention. He advises against relying heavily on nootropics for cognitive enhancement, suggesting instead to focus on natural methods like sleep and NSDR.