Evening light

Deep red

≈ 625 nm

Intensity
60%
Soft glow · ≈ 625 nm

Guide

About the light

Not a medical device

Circadia is for comfort, ambience and daily routine. A phone screen is far too weak to replace a red light panel or a 10,000 lux light box, and the app does not diagnose, treat or prevent any condition.

Three lights, two moments

Light is a signal for your body clock. Bright, white light in the morning says "day"; warm, dim red light in the evening says "wind down".

Deep red≈ 625 nm · eveningThe gentlest light for your body clock and night vision. Best for the last hour before sleep and at night.
Amber≈ 600 nm · eveningA warmer, slightly brighter glow for reading or relaxing, still very low in blue.
Morning sun≈ 5500 K · morningBright, daylight-coloured light to help you feel awake and start your routine.

What do "nm" and "K" mean?

nm stands for nanometre, one millionth of a millimetre. Light travels as a wave, and the length of that wave (the wavelength) decides its colour. Your eyes see roughly 400 nm (violet) to 700 nm (deep red); beyond about 700 nm is invisible near-infrared.

K stands for kelvin, the "colour temperature" of white light. Low values (~2700 K) look warm like a bulb; ~5500 K looks like midday sunlight; higher values look bluish. That's why Morning sun is described in K instead of nm: white light is a mix of many wavelengths.

What the screen light can do for you

A phone or computer screen is a gentle light source. Here's what it can realistically help with:

  • Deep red · in the eveningLets you see without the bright, blue-rich light that delays sleepiness. Keeps your night vision, so you stay calmer and fall back asleep more easily after waking at night.
  • Amber · relaxing & readingA warm, low-blue glow that's comfortable on the eyes and signals "wind down" while still giving enough light to read or relax.
  • Morning sun · after wakingA bright, daylight-coloured cue that can make you feel more alert and help build a regular wake-up routine. Real daylight outside is stronger still.
  • Breathe mode · any timeThe light rises and falls about 6 times a minute. Breathing along at that slow pace is a simple, well-studied way to feel calmer.
What it can't doA screen is about 100× too weak and has no near-infrared, so it won't give the skin, muscle or pain effects studied with red light therapy panels, or replace a 10,000 lux light box.

Why light in the morning helps

Bright light soon after waking is the strongest cue that keeps your body clock in time. It lowers leftover melatonin and boosts alertness, and over days it helps you feel sleepy at a regular time at night.

Best timingWithin the first hour after waking, for 10–30 minutes, with the screen at full brightness and close to your face's eye level (not staring into it).
Real daylight is strongerOutdoors, even on a cloudy day, gives 1,000–10,000+ lux. A phone screen gives a few hundred at most, so a walk outside or a window seat is even better.
Not a light boxClinical bright-light therapy uses about 10,000 lux light boxes. This screen is a gentle wake-up cue, not a treatment for seasonal or sleep disorders.

Red & near-infrared spectrum

Penetration depth & cellular impact

Longer wavelengths travel deeper before they are absorbed. Visible red light mostly stays in the skin, while invisible near-infrared reaches deeper tissue. This is why therapy devices pair 630–660 nm with 810–850 nm.

How deep red and near-infrared light penetrate the skin Approximate penetration depth by wavelength: 590 nm about 0.3 mm, 630 nm about 0.5 mm, 660 nm about 1 mm, 670 nm about 1.4 mm, 760 nm about 2 mm, 810 nm about 2.3 mm, 830 nm about 2.7 mm, 850 nm about 3.5 mm, 940 nm over 4 mm. Longer wavelengths reach deeper. VISIBLE RED NEAR-INFRARED · INVISIBLE 590 630 660 670 760 810 830 850 940 nm Epidermis 0–0.1 mm Upper dermis 0.1–0.5 mm Mid dermis 0.5–1.5 mm Deep dermis 1.5–3 mm Subcutaneous > 3 mm LIGHT PENETRATION INTO SKIN SHALLOWER DEEPER Surface & upper layers Muscles, joints & deeper tissue
Red · 630–670 nmAbsorbed in the outer few millimetres. Studied for skin, collagen and wound healing.
Near-infrared · 810–850 nmPasses deeper. Studied for muscles, joints and recovery.
Your phone screen · ≈ 600–630 nmVisible red only, about 100× weaker than a therapy panel and with no near-infrared, so it gives gentle ambient light, not these doses.

Depths are approximate and illustrative; they vary with skin type, power and study method.

Why red is gentler at night

Your eyes have a special light sensor (melanopsin) that tells your body clock it's daytime and holds back melatonin, the sleep hormone. It reacts most to blue light around 480 nm and barely at all to deep red.

Melatonin sensitivity across the light spectrum Sensitivity peaks at about 480 nm in the blue and is close to zero above 600 nm, where this app's light sits. This app peak ≈ 480 nm 400 500 600 700 nm Curve = how strongly light suppresses melatonin
MelatoninDeep red affects your body clock far less than white or blue light at the same brightness.
Night visionThe rods in your eyes barely respond to red, so your eyes stay adjusted to the dark. That's why astronomers and pilots use red light.

Screen light vs. therapy devices

Red light therapy (photobiomodulation) uses dedicated LED panels at 630–660 nm and invisible near-infrared at 810–850 nm, with much more power. A screen gives gentle ambient light, not a treatment dose.

Good for

  • Morning routineSun mode at full brightness while you stretch, wash or have breakfast.
  • Winding downA soft, warm red light for the last hour before sleep.
  • Getting around at nightSee your way without ruining your night vision or fully waking up.
  • Bedside & nurseryNight feeds or checking on someone without bright light.
  • Calm breathingBreathe mode rises and falls about 6 times a minute, a relaxed breathing pace.

How to use it

  1. 1
    Pick the light for the momentSun in the morning, at full screen brightness. Deep red or Amber in the evening, with the screen dimmed.
  2. 2
    Turn off Night Shift and True ToneThey tint the screen and change the colour you chose.
  3. 3
    Place it 0.5–1 m awayPoint it at a wall or the ceiling for an even, indirect glow.
  4. 4
    Set a timerThe light fades out over the last minute, and your session is saved to Stats.

What not to do

  • Don't use it as a treatment or instead of medical care.
  • Don't stare into the screen up close for long periods.
  • Avoid Breathe mode and very low brightness if you're sensitive to flicker or have photosensitive epilepsy.
  • Don't fall asleep with a bright screen beside your face. Use the timer.
  • Don't use Sun mode in the evening: bright white light at night delays sleep.
  • Don't expect it to fix ongoing sleep problems. Talk to a doctor if they last.

Sources

  • Brainard et al., J. Neuroscience 2001: action spectrum for melatonin suppression.
  • Lucas et al., Trends in Neurosciences 2014: measuring and using light in the melanopsin age.
  • CIE S 026:2018: melanopic light sensitivity.
  • Hamblin, AIMS Biophysics 2017: mechanisms of photobiomodulation.
  • Blume, Garbazza & Spitschan, Somnologie 2019: effects of light on human circadian rhythms, sleep and mood.
  • Terman & Terman, CNS Spectrums 2005: light therapy for seasonal and non-seasonal depression (10,000 lux).

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    Before you start

    Circadia turns your screen into a soft deep-red lamp for the evening, and a bright sun-like light for your morning routine.

    Not a medical device. It's for comfort and ambience only. A phone screen is far too weak for red light therapy.

    Tip: for a light that also covers the clock and battery bar at the top, add Circadia to your Home Screen (Share → Add to Home Screen).