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Being exposed to the right light at the right time can improve the quality of sleep and increase alertness during night-time work. This information comes from a new report by SSPA.

Sleep is a problem for many seamen. Watch hours and night work disrupt our body clocks (natural 24-hour rhythms), the ship is always moving and it can be difficult to fall asleep in the daytime. It is possible to improve the quality of sleep on board, however, even with relatively simple methods. Lars Markström at SSPA makes this claim after compiling the results of research studies on how light affects sleep and body clocks. During working hours, regardless of the time of day, wakefulness increases if people are exposed to light. Light reduces melatonin levels, a hormone that regulates tiredness and affects the basal ganglia cells that control body clocks. Natural outdoor light in the daytime makes us most wakeful, and that even applies to overcast days. People who have been outside during the day also find it easier to fall sleep in the evening. For those who are not able to be outdoors during working hours, or who work night watches, exposure to full-spectrum lamps that include blue light gives the best effect. However, it is not possible to see with the naked eye whether lighting is full spectrum, and blue light can be perceived as white light.

Yellow glasses
Light sources containing blue light described in a full-spectrum index should be under 2.0 to be considered as a good full-spectrum light source, according to Lars Markström. But the index has not yet been fully recognized, so you have to search a little to find the right lighting and possibly contact the supplier to obtain more information on the spectrum content. However, blue light should be avoided just before going to bed as it can prevent you from falling asleep. Most artificial light sources contain a certain amount of blue light, including telephone and computer screens.

”If it is not possible to avoid exposure to blue light, it can be blocked by using a pair of yellow or orange glasses,” says Lars Markström.

One drawback with coloured glasses is that they can impair colour vision in general, which could be a problem for certain tasks on board. There are glasses that only block blue light, but they are much more expensive.

Exposure to light can also be used to adapt body clocks to suit watch times and night work better. The report describes a method that the US Coast Guard recommends involving a slow adaptation over six days. On days one and two, your eyes are exposed to artificial daylight (blue) after sunset until 2 a.m. On days three and four, the exposure time is further increased until days five and six when the person is exposed to light until 7 a.m. Alertness at night-time is thus increased, and the time when tiredness comes is postponed until later in the morning.

The report is called Fartyg, människa och ljusmiljö (Ships, people and the light environment) and is financed by contributions from the Swedish Mercantile Marine Foundation. It is available in full, in Swedish, at under the tab for reports.

Lighting on board
• Blue light sources are preferable in workplaces where crew spend much time, such as the machine control room, the cargo control room and the galley, but also in the messes and lounges. If crew members wish to stay in these areas but avoid exposure to blue light, they are recommended to wear yellow or orange glasses.

• There should be access to both blue light and red light in cabins. Red light has a calming effect.

• Corridors, stores, washing rooms and other areas where crew only stay for short periods of time do not need special lighting.

• Cargo spaces on Ro-Ro ships may need blue light sources.

Source: The report on Ships, people and the light environment.

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