The seasons let us notice how much we need the daylight. Light lifts the spirits. The lack of light makes us feel tired. In the winter, we only receive a fraction of the light quantity that reaches us in summer. In addition, we spend the darker season mostly in artificially lighted rooms. This is why the quality of this artificial light is so important.
Light biologists, psychologists, doctors and lighting designers have been studying for some time how artificial light affects humans. Not only the photo-receptors in our eyes react to light stimuli. There is also a pigment in our organ of vision that reacts to light in the blue spectrum: Melanopsin – a protein in the retina of our eyes. Cells in our eyes containing melanopsin – a group of special, non-visual ganglion cells – let our brain know if it is day or night outside.
Light wakes us up!
Our retina is able to see electro-magnetic waves with a wavelength between 380 nm and 780 nm (nm = nanometer, one billionth of a meter). Between these wavelengths, all the colors of the light spectrum are found. Wavelengths just below the visible spectrum belong to the ultraviolet (UV). Above the visible spectrum is the infrared light (IR) or thermal radiation.
The intensity of light is measured in lux (the Latin name for light). Depending on which wavelength we receive in which quantity, our mood changes. When the summer sun radiates with its full light spectrum, with nearly 100.000 lux, it literally lightens our mood. The gloomy 3.500 lux during the winter months dampen our spirits. The intensity of light is especially small if we are inside buildings with artificial lighting. Therefore, the high quality of artificial lighting is very important.
The producers of lamps make an effort to offer high quality products on the market. However, very often the only criterion is the energy consumption and not the quality of the light itself.
How is the quality of light determined?
When we are outside on a sunny day, our body receives white light, infrared and ultraviolet. The light of a luminous element appears white to our eyes when all colors of its light spectrum are balanced. The release of melatonin – the sleep-hormone – in our body is regulated by blue light. This was a clever trick by nature. Humans evolved with daylight. When our ancestors spent most of the day under the blue sky (with hunting and gathering) our body suppressed the release of melatonin during the day. During a day spent outdoors, the melatonin level in the blood is low. The concentration of the sleep-hormone in our blood starts increasing at dusk, making us tired.
The effects of artificial lighting
Think of the lighting you normally find in schools, libraries, offices or hospitals. The most common thing are fluorescent lamps – either in neon tubes or as compact fluorescent lamps, the so-called “energy saving lamps”. Even today, brightness is the only quality criteria when it comes to interior lighting. In recent years, the question of energy efficiency was added, marking the end of the good old incandescent light bulb. However, the light of the incandescent light bulb is the closest to the natural sunlight.
Sunlight reaches the surface of the earth in a balanced color spectrum. Its light maximum is in the blue-green area with a wavelength of about 500 nm. Due to the brightness of the sun, our eyes perceive this as yellowish white.
Compared to the sunlight, the spectrum of fluorescent lamps has a significantly higher proportion of blue. And it is this blue portion that has a massive influence on our circadian rhythm, the waking and sleeping phases of our body. The blue portion of the light in our environment is important in the middle of the day, as it makes us awake and alert. Many of us work in front of screens that emit a light with a relatively high proportion of blue (flatscreen, tablet, iPad). This is why we should wear bluelight protect glasses when working in the evening, so that our circadian rhythm is not disturbed.
Bright artificial lighting
We need a clearly structured rhythm with enough light in the morning and correspondingly darkness in the evening, otherwise our wake-sleep rhythm gets confused. People who do not sleep well feel tired all the time and are easily unnerved. On the other hand, a sufficiently bright illumination during the day is important in offices, schools and universities. It is well-known today that people who study in optimal brightness are more concentrated, because a sufficient amount of light activates body, mind and mood.
Every cell in the body has its own circadian rhythm. One tenth of our genes are active during different times of the day and night. This is why concepts for optimal lighting are relevant, especially in hospitals and nursing homes, because body cells divide at specific times during the day, when the body regenerates. Patients and residents of nursing homes sleep better during the night if there was especially bright light during the day. However, this does not mean that there should be an overdose of blue light! The high proportion of blue light is a problem with fluorescent lights (gas discharge lamps) and LED flatscreens in particular. If this light is used in the evening, it alerts us and as a result, we do not sleep well.
This is why interior lighting and the work with screens and monitors should be planned. Illumination in offices should imitate and compensate the natural daylight. In this case, the light automatically adapts to the user needs and light requirements. The so-called “Smart-Lighting-Technology” means that the interior lighting is self-regulating, ensuring perfect viewing conditions and comfort for the users. The light could have a higher portion of blue in the early morning hours, getting warmer during the day.
Office workers could increase this “warming effect” by using bluelight protect glasses when working at the screen for longer periods or later in the day.
Sunlight is healthy
Humans feel comfortable in the natural light conditions of good weather: blue sky and sunshine – a mixture of a cold-blue sky and a yellowish-white, warm sun. Using corresponding lighting concepts changes the impression of offices significantly. The office is no longer a place where you go reluctantly, but is even inviting to stay longer.
Sunlight offers the full spectrum of colors as shown by the rainbow. Unfortunately, in the last few years the sunlight got a bad reputation. Due to the stratospheric ozone depletion, our fears of “damaging”, invisible UV-radiation have increased. But is this really justified? Again, this is a case of “the dose makes the poison”. Everybody knows that being exposed to sunlight for too long leads to sunburn. However, if the sunbath is regulated carefully – without sunscreen – it increases well-being and health. The sun is responsible for the production of vitamin D in the body, which regulates processes within the cell and stabilizes our skeleton. Vitamin D has also a protecting influence on our immune system. An optimal level of vitamin D in the blood is around 50 ng/ml (ng = nanogramm, 1 billionth of a gramm). Sufficient time in the fresh air and sun help the body to produce vitamin D.
However, our way of living has led to the fact that 90 % of the population suffer from vitamin D deficit. During the summer, most people avoid direct sunlight for fear of the “dangerous sun”. In the open air, the skin is immediately protected by sunscreen. Yet it is exactly this sunlight that has to reach the skin in order to produce vitamin D in the body, independent of the skin type.
It is important to know that the wavelengths of the UV portion of the sunlight is composed of the so-called UV-A-radiation (380 – 315 nm) and UV-B-radiation (315 – 280 nm). Relevant for the production of vitamin D is how much UV-B touches the skin. This portion is only included in the radiation of the summer sun between 11 a.m. and 3 p.m. When the sun is lower, the UV-B is absorbed by the atmosphere.
If the skin is exposed to sunlight without sunscreen, the vitamin D level in the blood increases. To reduce the risk of sunburn and skin cancer, too long exposure to direct sunlight should be avoided. However, 10 to 15 minutes are enough to produce up to 20.000 units of vitamin D. Of course, it is possible to supplement vitamin D in form of pills. But those who wish to regulate their vitamin D level naturally should always prefer daylight.
Light seems much too common for us to naturally know if there are factors that are good or bad for us. This article showed that light is not always light – meaning that light has a quality as well, and the higher this quality is, the more comfortable it is for our very sensitive organs of perception, the eyes and the skin.