☼ Your Circadian Rhythm

Your body runs on an internal 24-hour clock — the circadian rhythm — controlled by the suprachiasmatic nucleus (SCN) in your brain. This master clock governs when you feel alert, when you feel sleepy, your core body temperature, hormone release, and metabolism.

Two forces control your sleep:

• Process C (Circadian) — your internal clock that creates a wave of wakefulness during the day and sleepiness at night
• Process S (Sleep pressure) — a chemical drive (adenosine build-up) that increases the longer you're awake

When these two processes align, you fall asleep easily and sleep deeply. When they're misaligned — from irregular schedules, late light exposure, or stimulants — sleep quality collapses.

40 pts This is why Circadian Alignment is the highest-weighted section in your score. Nailing your rhythm matters more than any supplement or hack.

⏰ Fixed Wake Time — The #1 Lever

If you do only one thing to improve your sleep, make it this: wake up at the same time every day, including weekends.

Your wake time is the anchor that sets your entire circadian cycle. It determines when cortisol peaks (morning alertness), when melatonin rises (evening sleepiness), and when your body temperature drops (sleep onset trigger).

• A fixed wake time within ±30 minutes keeps your clock locked
• "Social jet lag" (sleeping in on weekends) shifts your clock by 1-2 hours — equivalent to flying across time zones every week
• Consistency of 6.5 hours beats inconsistent 8 hours

15 pts Wake time consistency is the single highest-scoring metric in the app. Your score compares your actual wake time against both your target and your 7-day median.

☀️ Morning Light — The Reset Signal

Light is the most powerful signal for resetting your circadian clock. Specifically, bright light in the first 60 minutes after waking tells your SCN: "It's morning — start the day cycle."

• Outdoor light is 10-100x brighter than indoor light, even on a cloudy day (~10,000 lux outside vs ~500 lux indoors)
• 10-30 minutes of morning light exposure advances your melatonin onset by 1-2 hours that evening — making it easier to fall asleep on time
• This works through specialised cells in your eyes (intrinsically photosensitive retinal ganglion cells) that detect blue-enriched light

10 pts Morning light exposure earns 10 points — the third highest individual metric. A simple yes/no: did you get outside within an hour of waking?

🌇 Evening Light Reduction

Light at night does the opposite of morning light — it delays your circadian clock and suppresses melatonin production.

• Even dim indoor lighting (100-200 lux) can suppress melatonin by 50%
• Screen light (phones, tablets, TVs) is particularly disruptive because of its blue wavelength content
• Walker recommends dimming lights 60-90 minutes before bed — think "sunset mode"
• Overhead lights are worse than side lamps (the angle matters to your retinal cells)

5 pts Evening light reduction is scored as a yes/no toggle. Did you dim down in the last hour before bed?

💤 Sleep Architecture — Quality, Not Just Quantity

Sleep isn't a single uniform state. You cycle through distinct stages every ~90 minutes:

• NREM Stage 1-2 — Light sleep, transition stages
• NREM Stage 3 (Deep sleep) — Physical restoration, immune function, memory consolidation. Dominates the first half of the night
• REM sleep — Emotional processing, creativity, learning integration. Dominates the second half of the night

This is why both duration and efficiency matter:

• 7.5-8.5 hours is the ideal range for most adults
• Sleep efficiency (time asleep ÷ time in bed) should be ≥85%
• Sleep latency of 10-20 minutes is healthy. Falling asleep in under 5 minutes actually signals sleep deprivation, not good sleep
• ≤1 awakening per night indicates consolidated sleep

30 pts The Sleep Architecture section captures duration, efficiency, latency, and awakenings — the measurable structure of your sleep.

Apple Watch integration (optional): If you record sleep stages (Awake, REM, Core, Deep) from Apple Health, the architecture score evaluates stage proportions against clinical guidelines (AASM) instead of using the simple duration estimate. Optimal ranges: REM 20-25%, Deep 15-20%, Core 45-60% of total sleep, and Awake under 5% of time in bed.

🧊 Temperature — The Sleep Trigger

Your core body temperature needs to drop by about 1°C to initiate sleep. This is one of Walker's most emphasised and least-known points.

• Ideal room temperature: 16-19°C (60-67°F)
• A hot bath or shower 60-90 minutes before bed paradoxically helps — it draws blood to the surface, which then radiates heat away, accelerating the core temperature drop
• Your circadian rhythm naturally dips your temperature in the early morning hours; a warm room fights against this
• Socks can help (warm extremities dilate blood vessels, releasing heat from the core)

5 pts Temperature optimisation is tracked as a behavioural habit in your check-in.

☕ Caffeine — The Hidden Saboteur

Caffeine works by blocking adenosine receptors — the molecule that builds up sleep pressure. It doesn't create energy; it masks tiredness.

• Caffeine has a half-life of 5-7 hours. A coffee at 2pm means roughly half the caffeine is still in your system at 9pm
• Even if you "can fall asleep after coffee," studies show caffeine reduces deep sleep by 15-20%
• Walker recommends no caffeine after 8+ hours before bed — ideally stop by 1-2pm
• This includes tea, chocolate, some medications, and energy drinks

5 pts Caffeine cutoff is a default behavioural habit. Did you avoid caffeine in the 8 hours before bed?

🍷 Alcohol — The Sleep Destroyer

Alcohol is one of the most misunderstood sleep disruptors. It may help you feel drowsy, but it devastates sleep quality.

• Alcohol is a sedative, not a sleep aid — sedation is not sleep. It suppresses brain activity rather than producing natural sleep patterns
• It fragments sleep, causing micro-awakenings you won't remember but that destroy sleep continuity
• REM sleep is heavily suppressed — this means impaired emotional regulation, memory consolidation, and creativity the next day
• Even 1-2 drinks can reduce REM sleep by 20-30%
• Walker is unequivocal: alcohol is one of the most potent REM sleep suppressors known

5 pts Alcohol timing tracks whether you kept to 0-1 drinks, none within 3-4 hours of bed.

🧠 REM Sleep & Emotional Regulation

REM sleep isn't just about dreams — it's your brain's emotional processing centre. Walker describes it as "overnight therapy."

• During REM, your brain replays emotional experiences but strips away the emotional charge, helping you process difficult events
• Poor sleep (especially REM loss) increases amygdala reactivity by up to 60% — making you more anxious, reactive, and emotionally volatile
• Chronic REM deprivation is linked to anxiety disorders, depression, and PTSD
• This is why the refreshedness and tiredness onset metrics matter — they're proxies for how well your REM sleep did its job

20 pts The Wellbeing Wellbeing section (refreshedness + tiredness onset) is your daily signal of how well your sleep performed its restorative function.

⚡ Sleep Debt Is Real

One of Walker's most important warnings: you cannot "get used to" insufficient sleep. You simply lose awareness of how impaired you are.

• After 10 days of 6 hours sleep, cognitive impairment equals someone who has been awake for 24 hours straight
• Wellbeing sleepiness plateaus after a few days of short sleep — but objective performance keeps declining
• Sleep debt accumulates and cannot be fully repaid by weekend lie-ins (these actually worsen circadian disruption)
• Chronic short sleep (<7 hours) is linked to increased risk of Alzheimer's, heart disease, diabetes, obesity, and weakened immune function

Key This is why the app tracks trends over time, not just single nights. Your Reports screen reveals whether you're building a sleep surplus or accumulating debt.

📅 Consistency Beats Duration

Perhaps Walker's most counterintuitive insight: regular 6.5 hours of sleep outperforms irregular 8 hours on nearly every health and performance metric.

• Irregular sleep schedules confuse your circadian clock, reducing sleep efficiency and fragmenting sleep stages
• The body "prepares" for sleep based on your habitual schedule — inconsistency means your body doesn't know when to start the process
• Shift workers, who have the most irregular schedules, have significantly elevated rates of cancer, cardiovascular disease, and metabolic disorders

Key The app weights consistency heavily. After 3+ entries, your wake and bed time scores factor in deviation from your 7-day median — rewarding regularity, not just hitting a target once.

🎯 The 4 Highest-ROI Moves

If you want maximum return on effort, focus on these four. Everything else is optimisation on top.

Combined, these four habits account for 40 of your 120 raw points (33% of your score) and are the foundation everything else builds on.

📊 How Your Score Maps to the Science

The scoring system is weighted to reflect what the research says matters most:

Raw scores (out of 120) are normalised to 0-100 for simplicity. Colour coding: ≥80 great, 60-79 fair, <60 needs work.

📚 Further Reading

• Why We Sleep — Matthew Walker (2017). The foundational text for this app's scoring model
• The Circadian Code — Satchin Panda. Deep dive into time-restricted eating and circadian biology
• Internal Time — Till Roenneberg. The science of chronotypes and social jet lag
• Huberman Lab Podcast — Episodes on sleep, light exposure, and circadian health