Light & Zeitgebers
Morning sunlight, lux dose, blue light, red light, dawn simulators, with the research.
Light is the primary circadian zeitgeber. Dose, timing, wavelength, and the buying guides for tools that deliver the right light at the right time.
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Pick the piece you're solving for.
Each topic opens with the protocol or explainer to start from, then groups the related posts under it, down to the dose-tested gear where it applies.
Morning light dose
The primary zeitgeber: lux x minutes, the 60-minute window, and the Phase Response Curve behind it.
Start here: Morning Sunlight Protocol: Dose, Timing, WavelengthLight therapy & SAD lamps
When indoor light therapy is warranted, the dose it needs, and the lamps that actually deliver it, measured.
Start here: Light Therapy for SAD and Winter Depression, ExplainedResetting your rhythm
The practical sequence for dragging a drifted clock back, using light first and timing everything else around it.
Start here: How to Reset Your Circadian Rhythm: The ProtocolEverything else in scope.
Cortisol and Sleep: The Morning Hormone That Times Your Wake-Up
Cortisol is not only a stress hormone; it follows a strong daily rhythm that peaks in the early morning to drive waking and falls to its low at night to allow sleep. What the research says about the cortisol awakening response, how stress and disrupted sleep push the rhythm out of shape, and why fixing the rhythm matters more than chasing a single cortisol number.
Eating Before Bed and Sleep: What a Late Meal Does to Your Night
A late meal is not automatically bad for sleep, but eating large, heavy, or the wrong foods close to bedtime reliably disturbs it, and meal timing is also a signal to your body clock. What the research says about reflux, blood sugar, and circadian meal timing, and how to eat in the evening without wrecking your night.
What Happens When Your Circadian Rhythm Is Disrupted
Your body clock does far more than control sleep; it schedules hormones, metabolism, temperature, and alertness across the day. When behavior falls out of step with the clock, through shift work, jet lag, social jet lag, or erratic light, the misalignment shows up as poor sleep, daytime dysfunction, and, over the long run, metabolic and mood consequences. What the research says, and how the clock realigns.
Verilux HappyLight vs Carex Day-Light: Which Lamp Wins
A head-to-head on the two most-cross-shopped light therapy lamps, judged on the one metric that matters: measured lux at the distance you actually sit. Panel size, dose at 12-24 inches, UV filtering, and who each is for.
How to Wake Up Early: The Circadian Protocol That Works
Waking up early is a circadian-phase problem, not a willpower problem. The fixed wake time, the morning-light dose, the evening-light guard, and the 15-30 min/step schedule that advances your clock ~0.5-1 hour a week.
Do Dawn Simulators Work? The Evidence on Gradual-Light Wake-Up
Dawn simulators wake you with gradually brightening light instead of an alarm. What the trials show for alertness, mood, and easier waking, where the effect is real versus overstated, and how they compare with a proper morning-light dose.
Red Light at Night: Does It Really Protect Sleep?
Red and amber light suppress melatonin far less than blue-white light at equal intensity, which is why night lights and evening bulbs shift red. What the action-spectrum data show, the practical wavelength and brightness targets, and where the claims outrun the evidence.
Do Blue Light Filters and Night Mode Actually Help Sleep?
Night Shift, dark mode, and blue-light filter apps warm the screen to cut short-wavelength light. What the melatonin and sleep trials actually found, why brightness and use time matter more than color, and where the claims outrun the data.
Evening Light Hygiene: The Wind-Down Protocol
Bright evening light is the single most common thing keeping a healthy clock late. The lux targets, the timing window, how to handle overhead lights and screens, and where blue-blockers actually fit, with the melatonin-suppression evidence behind each step.
Spring Fatigue (Frühjahrsmüdigkeit): Why the Longer Days Can Leave You More Tired, Not Less
Spring fatigue, the German Frühjahrsmüdigkeit, is the run of tiredness, low drive, and heavy limbs many people report as winter turns to spring. It is a folk concept rather than a medical diagnosis, and the direct evidence is thin, but the plausible drivers are circadian: a body clock recalibrating to longer days, a melatonin and serotonin transition, the added jolt of the clock change, and circulation adapting to milder weather. What the research actually supports, what helps, and when the tiredness is pointing at something else.
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