Warm light and sleep are more closely linked than most people think. It is not the amount of light in the evening that determines a peaceful moment of falling asleep, but rather its color and blue light content. Warm, blue-depleted light signals to the body that the day is drawing to a close. Cool light with a high blue content does the opposite. This article explains why this is and how you can align your evening light accordingly.
The Quick Answer
In the evening, warm light helps you fall asleep because it contains almost no blue light and is less disruptive to the release of the sleep hormone melatonin. As bedtime approaches, the light should become warmer and dimmer. Conversely, cool, bright light late in the evening keeps you awake. A gradual transition throughout the evening is key, rather than a single switch.
Why Light Regulates Sleep
The body has an internal clock that is heavily guided by light. Through special receptors in the eye, it primarily measures the blue light content. A high level of blue light signals daytime and alertness to the body. A low level of blue light means evening and rest. For thousands of years, this regulation aligned with natural sunlight, which naturally becomes warmer and dimmer in the evening.
Artificial light disrupts this rhythm. Sitting under bright, cool light in the evening continues to signal daytime to the body. As a result, the transition to sleep is delayed.
Blue Light Content and Melatonin
The sleep hormone melatonin naturally rises in the evening to make us feel tired. Light can suppress this rise, and blue light does so with particular intensity. A widely cited study showed that exposure to room light before bedtime significantly delays the onset of melatonin and shortens the duration of melatonin secretion compared to dim light (Gooley et al., Journal of Clinical Endocrinology & Metabolism, 2011, PubMed 21193540).
In this context, it is not only the brightness that matters, but also the spectrum. A study in Physiology & Behavior compared blue-depleted LED light with standard light at bedroom brightness levels, finding that the blue-depleted light resulted in significantly less melatonin suppression (2017, Vol. 177, DOI 10.1016/j.physbeh.2017.05.002). Warm light with a low blue content is therefore the more sleep-friendly choice for the evening.
Daylight Matters Too
The evening is only one half of the equation; the day is the other. Exposing yourself to plenty of bright, cool daylight during the day strengthens your circadian rhythm and makes your internal clock more resilient to disruptions in the evening. A clear contrast between a bright day and a warm, dim evening has a stronger effect than a daily routine illuminated uniformly across all hours. Warm evening light, therefore, unfolds its best effect when the day has been filled with sufficient bright light.
Warm Light in the Evening: What This Means in Practice
Warm light is recognized by a low color temperature in Kelvin. Anything below approximately 2,700 Kelvin feels warm; shortly before sleeping, values around 1,800 to 2,200 Kelvin are ideal, as they evoke candlelight and contain virtually no blue light. Which Kelvin values suit each zone in the bedroom is detailed in our Kelvin Guide for the Bedroom.
What matters most here is the interplay between light color and brightness. A warm color temperature only has a calming effect when the light is also dimmed. Full brightness at 2,700 Kelvin is still brighter than the body needs late in the evening.
Specifically at GRAU: At its warmest setting, Salt glows at 1,300 Kelvin—warm light without any blue content. This is lower than what many bedside lamps offer, making it the perfect fit for the final hour before sleep.
The Evening Lighting Routine
The most effective leverage is not a single product, but a routine. Light should become warmer and dimmer throughout the evening, mimicking the natural sunset outside. A simple framework:
| Time | Light color | Brightness | Goal |
|---|---|---|---|
| Early evening | warm white around 2,700 K | medium, dimmed | Unwinding after the day |
| 1 to 2 hours before sleep | 2,200 K | low | Preparing the body for rest |
| Directly before sleep | 1,800 to 2,200 K | very low | Do not disturb falling asleep |
Three points make all the difference:
- Avoid cool, bright light late in the evening. This applies to ceiling spotlights as well as screens.
- Use several small, warm light sources instead of one bright ceiling light. This keeps the lighting low and calm.
- Make the transition gradual. An abrupt shift from bright to dark is less effective than a smooth, sliding progression.
Warm Dimming: Light Color Follows Brightness
Standard luminaires only get dimmer when dimmed, not warmer. For sleep, however, it is precisely this combination that is crucial: less brightness and less blue content at the same time. Luminaires that automatically become warmer as they dim handle this transition for you. This is exactly what Sunset Dimming does, tracing the curve of a sunset. At your bedside, the cordless Salt takes on this task, while Sun provides a calm baseline light in the room.
How to Adapt Your Home
You do not need to redesign your entire home. For better sleep, a few targeted adjustments in your bedroom and evening environment are enough:
- Place a dimmable, warm luminaire by the bed that can be adjusted down to very low levels.
- Late in the evening, use only this warm island of light instead of turning on the bright ceiling light.
- In the bathroom, which many enter shortly before bed, choose a warmer and dimmable solution where possible.
- Reduce screen time late in the evening or switch devices to a warm display mode.
- Keep consistent times. The body responds better to a regular routine than to occasional good evenings.
Common Mistakes
- Bright, cool white bathroom or ceiling light directly before bedtime.
- A single bedside lamp that cannot be dimmed deeply enough.
- Warm light that has the correct color temperature but is run at full brightness.
- Reaching for your phone in bed, as its cool display undoes the positive effect.
The Takeaway
Good sleep does not start once you are in bed, but with the lighting in the evening. Shaping the last hours before sleep with warm, dimmed, and low-blue light means working with your body rather than against it. The principle behind it is simple: warm light color, low brightness, and a gradual transition.