During the day, most people work in buildings and very often on computer workstations. There, we clearly get too less of natural day- and sun-light. Because, the difference between inside and outside is huge. Well lit offices have a light intensity of about 700 to 800 lux. A sunny day far more than 100.000 lux. But, we do need the light for the light-depending hormonal balance of the “happiness” hormone serotonin and the “sleeping” hormone melatonin. Tests show that this is only possible from about 3,000 lux – better would be 10,000 lux. Here, we talk about white light.
Sleepless at the screen
A rather new, sleep disturbing phenomenon are LED-screens. These screens often have a high share of day- or blue-light. But, blue-light is waking up the brain again and is disturbing our biological clock. Meaning, the one who is working late in front of the screen and checking his emails doesn’t have to be surprised that he is wide awake afterwards. For the most of us, electronic devices with thin and light screens became permanent companions. A last look on to the display even became the very last thing to do before going to sleep. But, besides from distraction and information the display delivers something else: an extra portion of artificial light with a high share of blue-light.
Sleep scientists around Prof. Christian Cajochen and Dr. Sylvia Frey from the University Clinic in Basle, Switzerland, examined under controlled conditions how strongly the light of an ordinary LED-screen is influencing our inner clock. Five hours before their normal sleeping time, two test persons sat for the coming hours in front of two different screens. The first screen was an older one – a flat screen with a fluorescent tube – and the other one a LED-display, which is emanating blue-light three times as much.
The test persons were busy the whole time, they were doing reaction tests, informing about their subjective sleepiness, and had to proof their memory performance. In regular intervals, the scientists took saliva-samples to measure the melatonin-level which was supposed to continuously rise the closer the regular sleeping time came.
The sleep scientists monitored the experiment in the control room and were able to objectively judge the sleepiness of the test persons by measuring the batting of the eye lids as well as the brain waves. The findings were clear: the participants on the older screens got tired at their usual sleeping time. They began to roll with their eyes and their brain waves got longer, as expected.
With the participants on the LED-screens it was completely different: although they were supposed to get tired, too, their batting of the eye lids and their brain waves hardly changed. Finally, the results of the melatonin measuring fit the observations. Because of the light of the light-emitting diode on the LED-screen the natural formation of the sleeping hormone got delayed by about one hour. This makes it to another scientific proof: when provoking a suppression of melatonin one is preventing the body from preparing for sleep in a naturally and healthy sort of way. By that, it is easily explained why more and more people are suffering under problems to fall asleep right after turning off the screen.
Already in 2001, neuroscientists from the Jefferson Medial College have proven in a test that the wave of blue light (446 – 477 nm) has the highest impact on the melatonin level in the blood. The consequences out of this are shown in a Japanese study where especially many people are sitting in front of the screen until very late. According to that, 53.7 of all internet user go to bed very late, 45.4 per cent of them are having too less and a non-recreational sleep.
When you are not able to avoid working in front of a screen the last two hours before going to bed you at least should set the display as reddish as possible or use special glasses that filter out the blue-light of the screen.
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This post is also available in / Diesen Beitrag gibt es auch in: German