Reporter 405, 30 June 1997


Bright light is the clue to a good night's sleep

No-one really knows why we need sleep, but clearly going without it reduces our ability to function properly. Shift workers in particular have more accidents and lowered concentration levels at work because of poor quality sleep. Pioneering research by a Leeds psychologist is demonstrating how exposure to bright light while working at night can improve the concentration of shift workers – and help them sleep better during the day.

Abnormal sleep patterns can, literally, damage your health, writes Gill Moffett. A study carried out by Dr Lawrence Smith, of the Department of Psychology, revealed a 20 percent increase in injuries on the night shift compared with day working on the same processes.

The difference is thought to be caused by poor sleeping patterns and the mismatch between the body's 'internal clock' and what the environment is telling them.

The body clock, situated in the hypothalamus in the brain, works by timing our bodily processes so that they peak and trough in a regular, predictable cycle over 24 hours. If left to its own devices, without the influence of external time cues, the body clock tends to run closer to 25 hours. But we are heavily influenced by our environment so our biological rhythms are trained to time cues such as the day-night cycle, social activity and even our knowledge of clock time resulting in "a natural" 24-hour cycle.

It is believed that having a body clock gives an evolutionary advantage. So, instead of simply responding to changes in the environment as they happen, such as sunrise, the body clock helps us anticipate and prepare for the change. It gets the system 'warmed-up' and ready for activity.

Dr Smith is researching the effects of shift working and how people cope with the disruption to their body clocks.

The work includes an analysis of 'zones of vulnerability' over the 24 hours – times at which people face greater risk of accidents because performance capabilities are naturally at a low ebb; around midnight to 5am and from around 2– 4pm. He has looked at a range of industries, including nuclear power, the police, health services, chemical processing, food production, and steel and vehicle manufacture, all of which rely on people working at night.

Dr Smith says the challenge of this work is to find ways to improve conditions for people who must work regularly at night. "The common catch-all solution is to implement a 'better' shift system that is less disruptive to the workers concerned," he said. "But, in reality, employees still have to work at night so we have to find ways of reducing the vulnerability of people on night work." His latest research involves a 'light lab' which will be set up in the Department of Psychology to examine a new idea in improving conditions for shift workers.

Light has a powerful influence on the human body clock. One approach to alleviating night-time problems is to use bright light in the workplace to help shiftworkers alter their body clock so that they are alert and effective at night, and are able to sleep adequately during the day. The light used will have an intensity of between 1500 and 2500 lux – "about 20 per cent of the light levels of an overcast summer's day." This is much brighter than ordinary office lighting, which may be around 500 lux or less.

The aim of using the bright light is to 'nudge' the body clock into delaying for a few hours. This means that alertness levels should peak during the early hours of the morning but also that sleep should be easier during the day. In some studies, sleep durations which are typically short and poor quality following night shifts have been extended for up to two hours following night exposure to bright light. Exposure times of as little as a couple of hours have been shown to be effective.

The light lab will study people performing simulated work tasks and assess the impact of different light intensities and exposure times. In addition, the light lab will function as a resource for undergraduate and postgraduate study. It will be a unique, high-profile facility that will represent a national resource. There is already interest from industry in the potential benefits of this innovation.

Dr Smith and Dr Peter Gardner, also from Psychology, have secured funding from the nuclear power industry to explore the effects of bright light on shiftworkers' well-being and their performance on work-related tasks. The 'light lab' will place the University of Leeds in the forefront of applied research in this area. Further links with industries that operate over 24-hours, such as the financial sector, chemical processing industry and emergency services, are being sought.

The Shiftwork and Safety Research Group headed by Dr Smith has been granted £35,000 to set up the basic light laboratory by a combination of University and Royal Society support and £104,000 over two years from Nuclear Electric/BNFL to carry out a number of research studies.

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