Light intensity affects a person’s cognitive function and sense of alertness, a Swiss study reveals. After a series of tests, they found that those who were subjected to a higher light intensity in the afternoon were more alert until early in the evening.
In the experiment conducted in the EPFL’s Solar Energy and Building Physics Laboratory (LESO), experts confirmed the old belief that lighting affects a person’s perception of sleepiness. But aside from stimulating the sense of alertness, experts found that the brighter the light is, the better people’s cognitive performance becomes.
Mirjam Münch, the lead author of the study, and her team wanted to know how people’s biological process of sleeping is affected by their perception of light during daytime. To do this, they recruited 29 young people and ask them to stay in a lab office with various lighting conditions. The experiment lasted for over two eight-hour sessions. During the first session, participants spent six hours in a room which has a lighting condition that’s similar to the natural light at around 1000-2000 lux. In the second session, the researchers reduced the light intensity to 170 lux – a condition wherein the participants perceive light in an enclosed room without a window and lit with artificial light.
Lighting Intensity and Cognitive Performance
To ensure that the participants have the same internal biological clocks, they were asked to maintain a regular sleeping schedule for seven weeks before going through the experiment. They were also given bracelets with built-in sensors and accelerometers so the scientists can detect and monitor their movements while inside the experiment office. And every 30 minutes, the researchers assessed the participants’ level of alertness.
For the final assessment at each session day, the participants had a supplemental memory test in a darkened room (has light intensity of 6 lux) which run for 3 hours. At the end of the trial, the researchers took saliva sample from each of the participants to measure the concentration levels of their melatonin (hormones that regulate sleep) and cortisol (hormones released in response to stress) which are produced by the body after every 24-hour period.
The results revealed that the participants who were subjected to a higher light intensity during the afternoon were more alert as compared when they were subjected to the light intensity that is 10 times lower. Said level of alertness was sustained until early in the evening. The same is true with their cognitive performance, as reflected in the scores they got from the memory tests.
The researchers arrived on the same results even when there was no change in the participants’ cortisol and melatonin levels.
According to Münch, the study showed a direct relationship between the feeling of sleepiness as well as the cognitive performance and light intensity. She added that such benefit can be observed for such a period of time after the exposure. Their findings have been published in the journal Behavioural Neuroscience.
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