The Seluna Sleep Guide

Nine evidence-based levers that fix broken sleep — light, caffeine, temperature, timing. Free, no products required.

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Why sleep falls apart — and how to fix it

Most sleep advice stops at "go to bed earlier." That ignores how sleep actually works. Sleep is not one long state of unconsciousness — it is a regulated cycle of stages, timed by two biological systems: circadian rhythm (your internal 24-hour clock) and sleep pressure (a molecule called adenosine that builds in your brain all day and clears at night).

When sleep is bad, one or both systems are being disrupted. Fix the inputs and sleep usually follows. This guide covers the nine inputs with the strongest evidence.

1. Light: the master switch

Your circadian clock lives in a cluster of neurons behind your eyes that synchronize to light. Bright light in the morning sets the clock; bright light at night delays it.

Morning: Get 10+ minutes of outdoor light within an hour of waking. Outside light is 10–100× brighter than indoor light, even on a cloudy day. This is the single highest-leverage habit in this guide.
Evening: Dim household lights after sunset. Overhead lights are the worst offenders — use lamps at seated height.
Before bed: Screens are less about blue light and more about engagement. If you use screens late, drop brightness, hold the phone further from your face, and stop anything work-adjacent 60 minutes before bed.

2. Caffeine: the 10-hour rule

Caffeine blocks adenosine receptors — it does not create energy, it hides the fatigue signal. Its half-life is 5–6 hours, so a 3 PM coffee leaves a quarter of the dose active at 1 AM.

Cut off caffeine 8–10 hours before bed. For a 10:30 PM bedtime, that means your last cup is around 12:30–2:30 PM.
If you sleep 7+ hours and still wake tired, test a full caffeine cut for two weeks before blaming anything else.

3. Alcohol: sedation is not sleep

Alcohol is the most common self-prescribed sleep aid, and it works — for the first hour. Then it fragments the second half of the night, suppresses REM sleep, and rebounds with lighter sleep and awakenings as it metabolizes.

If you drink, keep it 3+ hours before bed and keep it to 1–2 drinks.
Judge alcohol's cost by how you feel at 3 AM, not at bedtime.

4. Temperature: cool the room, warm the body

Sleep onset is tied to your core temperature dropping about 1°C. You fall asleep faster when the room is cool and your body can dump heat.

Set the bedroom to 17–19°C (63–66°F).
A warm bath or shower 1–2 hours before bed paradoxically helps: it pulls blood to the skin, which accelerates the core temperature drop afterward.
Warm feet help, warm core hurts — socks yes, heavy duvets no.

5. Consistency beats duration

Your circadian system rewards regularity more than it rewards duration. Both enough sleep and a regular schedule matter. Most adults need at least seven hours, and many need more.

Wake at the same time every day — including weekends. Wake time anchors the clock; bedtime follows.
Keep the drift under 1 hour if you can.

6. Naps: short and early

Naps are fine — long and late naps are not. They release sleep pressure you need at night.

Keep naps under 25 minutes, and finish them by 3 PM.
If you can't sleep at night, skip naps entirely for two weeks.

7. The wind-down: give sleep a runway

Sleep does not switch on like a light. A 30–60 minute buffer of low-stimulation activity teaches your brain what comes next.

Pick 2–3 repeatable actions: shower, stretch, read paper fiction, journal.
Reserve the bed for sleep. If you are awake for more than ~20 minutes, get up, do something calm in dim light, and return when sleepy.

8. The bedroom: dark, quiet, boring

Dark: blackout curtains or a sleep mask. Even closed eyelids register light; a 100-lux nightlight measurably lightens sleep.
Quiet: consistent noise beats sudden noise. Earplugs or a fan for white noise.
Boring: no visible clock. Checking the time during night wakings produces arousal and fragmented sleep.

9. When to see a doctor

Self-experimentation has limits. Talk to a clinician if any of these apply:

You snore loudly, wake gasping, or feel unrefreshed despite 7–8 hours — possible sleep apnea.
You cannot fall asleep for 30+ minutes most nights for over a month — possible chronic insomnia; CBT-I (cognitive behavioral therapy for insomnia) is the first-line treatment, not pills.
Restless legs, limb movements, or new daytime sleepiness that interferes with driving or work.