How light affects health

Even single-celled organisms, the smallest of living things, strive for it. Plants turn their flowers and leaves toward it. And for humans, it is one of the most important staple foods for the psyche and the biorhythm. It makes us happy and cheerful, calms us and builds us up, but it can also stress us, make us sad and tired – especially when it is absent or in short supply.

We realize how important light is for our well-being, especially when it is lacking – during the dark season or when the sky is overcast for days or even weeks. About 20 percent of people in Germany feel down due to this lack of light: they become melancholic and withdraw.

Lack of light can affect the mood

Combined with listlessness, chronic fatigue, and exhaustion, these are typical signs of Seasonal Affective Disorder (SAD), the so-called winter depression. It occurs in about two percent of the population. Since it is a form of depression it should also be treated by a doctor – supported by light therapy.

Light has a positive effect on body and mind, even some blind people feel it. Despite non-functioning cones and rods in the eye, through which we perceive light stimuli and the brain is supplied with information about brightness, darkness, and colors, their internal clock adapts to the natural light-dark rhythm. Researchers from the Salk Institute for Biological Studies in San Diego assume that the affected people can feel the light.

Anyone who has ever been in a ganzfeld by US artist James Turrell knows this phenomenon. A completely empty room that is slowly flooded with changing colored light. Visitors describe a feeling of disorientation and a strange state of suspension. Turrell himself calls this experience "feeling with the eyes."

All over the world he makes rooms glow, bringing the sky to the earth with his Skyspaces. How overwhelming and magical his light installations are can be experienced, for example, in the Skyspace Lech on the Tanegg (skyspace-lech.com) and since last year also in the Freising Diocesan Museum (dimu-freising.de) experience.

© (c) Lech Zürs Tourismus by Florian Holzherr

The Skyspace Lech is open all year round.

Actually, it is Eye one of the best and longest researched organs. How seeing with rods and cones basically works has been known for more than 170 years. But it was only in the early 2000s that scientists began to scientifically trace the quoted feeling with the eye.

It had long been suspected that there should actually be other receptors in the retina. It all started with the American neurobiologist George Brainard, who discovered ganglion cells that react particularly to light with a high blue content. The American neuroscientist David M. Berson finally found the light-sensitive pigment melanopsin in these cells.

In a way, the missing link for biochemical reactions of the human body to visual stimuli. This protein essentially functions as an on/off switch for our internal clock. It starts and lowers hormone production, thus also regulating heart rate, breathing, and body temperature. If it detects blue light, i.e., the typical daylight frequency, the release of the sleep hormone melatonin is stopped.

In recent years, this discovery has led to new developments in various fields – from sleep research in medicine to the lighting industry, which is making use of blue light findings.

Light needs shadow

There are spaces where we spontaneously feel comfortable and others that evoke unpleasant feelings in us. A decisive factor here can also be the light or lighting. Because: Brightness alone does not make you happy; the change between light and shadow is more important. If a room is completely illuminated, the contrasts are missing. Unconsciously, a feeling of oppression sets in. What does this mean for lighting design – how is feel-good light created?

Ideally through a mix of spotlights, indirect light, and light islands that create light and shadow as well as provide structure and depth. Therefore, every room needs different light sources. In the dining area, for example, one or more lights above the table, adjustable floor lamps, as well as ceiling spotlights or floodlights.

Furthermore, the light should be focused and not diffuse, like that from lamps with satin glass. Colors thus stand out more and are as brilliant as in sunlight. For the feel-good effect, it is also important not to look into the dark. Meaning: Everything that is in the field of vision - this can also be the hallway when sitting at the table - should be illuminated.

© Kat Smith

Light has an extreme effect on our well-being.

How to use light ideally?

Everyone knows this from traffic: When we are dazzled, we find it unpleasant, become tired and unfocused over time. That's why lamps, in whose light we look, have no place in the home or office. While pinpoint light is ideal at the dining area because it perfectly stages the food, the desk should be bathed in light that illuminates the table evenly and casts no shadows.

In both cases, indirect room light that brightens the ceiling or wall in places creates an atmosphere. Light planners swear by dimmable lamps, whose light can be adjusted to the time of day and needs. For example, in the morning or when we want to be active, we need brighter light, while with a smaller amount of light we automatically switch to relaxation or rest mode.

The light or color temperature is also crucial, measured in Kelvin (K). The guideline is: the higher the Kelvin number, the bluer and thus cooler the light. Daylight corresponds to 5,000 Kelvin (or more) and is used for light therapy, among other things.

So-called cold white (3,500 to 5,000 Kelvin) is close to the morning sunlight and is often used in offices because it promotes alertness and concentration; in the home office, 3,000 Kelvin is usually sufficient. For living or dining rooms, warm white, inviting, and relaxing light of 2,700 Kelvin or less is ideal.

Light as a mood booster

Light is our internal clock. When it gets bright in the morning, the light-sensitive cells in the retina signal the brain to secrete less melatonin (also known as the sleep hormone). If we are exposed to artificial light at night (because we work regularly) or lack daylight in winter, the sleep-wake rhythm is disrupted.

The result: You feel permanently tired, often lacking energy. And this is exactly where light therapy comes into play. With so-called light lamps, the lack of (sun)light is supposed to be compensated. The devices emit very bright, white light, about 100 times stronger than a conventional light bulb. With 6,500 Kelvin and a strength of around 10,000 Lux, it corresponds to natural daylight.

People who suffer from autumn-winter depression are recommended a 30-minute light shower to support therapy. Right after waking up, it should stop the release of melatonin and boost the production of serotonin - the hormone that triggers feelings of happiness and lifts the mood.

For more than half of the patients, a positive effect is noticeable after two to five days, which lasts for about a week. Nevertheless, scientists are divided on whether or to what extent light therapy helps to brighten the mood. However, they all agree that it certainly does not harm.