Your eyes contain special cells called intrinsic photosensitive retinal ganglion cells (ipRGCs) that detect light, specifically blue light around 480nm wavelength.

These cells send signals directly to your suprachiasmatic nucleus (SCN), the master clock in your brain that controls your circadian rhythm.

When blue light hits these cells, your brain interprets it as 'daytime' and suppresses melatonin production while increasing cortisol and alertness.

This system evolved over millions of years when the only light source was the sun during the day and fire at night. We have no mechanism to diferentiate artificial light from sunlight.

Melatonin is your body's primary sleep hormone, produced by the pineal gland. Its production is directly controlled by light exposure.

Blue light exposure suppresses melatonin production by up to 85%, even at relatively low intensities common in household lighting.

This suppression doesn't just affect sleep onset, it reduces sleep quality, REM sleep duration, and overall restorative benefits.

Red and amber light (above 600nm wavelength) have virtually no effect on melatonin, allowing natural sleep preparation.

Circadian rhythm affects far more than sleep. It controls hormone release, body temperature, digestion, immune function, and cellular repair.

Chronic circadian disruption is linked to increased risk of obesity, diabetes, cardiovascular disease, depression, and certain cancers.

Your circadian clock influences when you're most alert, creative, and physically capable, misalignment means you're never operating at peak performance.

Studies show shift workers and those with chronic light exposure at night have significantly higher health risks across multiple conditions.