Spectral control of illumination for accelerated physiological adjustment to shift work

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In the long run night work can contribute to the genesis of serious health impairments and probably promote the growth of malignant tumors. Decisive elements in this process are the chronodisruption along with light-induced suppression of melatonin synthesis. This application focuses therefore on the maintenance of melatonin synthesis while working single night shifts or while working longer night shift periods or permanent night shifts on the successive shift of melatonin production into day sleep. Contrary to former studies this effect will be achieved not by alterations of light intensity but by controlled variations of the spectral composition (colour temperature) of light. In consideration of visual performance these variations will be limited to the spectral composition of white light. Following these preconditions the effects of seven pre-selected light spectra on visual performance will be examined experimentally with 16 young persons with normal colour vision. The effect on melatonin synthesis will be tested in experiments over 6 hours each (20:00 to 02:00). Based on the results two spectra, one with high and one with low melatonin suppression (high/low blue-share) will be selected for further experiments. A special control will be developed that converts both spectra into each other.The following experiments will be again completed with 16 healthy young persons with normal colour vision. To maintain melatonin synthesis during single night shifts light with initially low melatonin suppression will be converted at the end of the night shift into light with high melatonin suppression. In two consecutive nights melatonin profiles will be ascertained with half-hourly saliva samples (22:00 to 06:00), the basic profile in the first night (30 lux), in the second night under the impact of the light scenario and experimental shift work. Longer lasting night shift periods require the successive shift of the melatonin profile into day sleep. For this light with initially high melatonin suppression will be during 3 consecutive night shifts converted (in the first night shift after 4, in the following night shifts 1 or 2 hours later) into light with low melatonin suppression. The phase shift will be quantified with 24hour Phase Assessment Procedures before and after the three work shifts. The melatonin profile will be ascertained with hourly saliva samples. During all night shifts salivary melatonin concentrations, visual and cognitive performance and fatigue will be ascertained hourly.To accomplish this basic research at the interface between lighting technology and medicine this application is made by members of the Leibniz-Institutes für Arbeitsforschung (Dortmund) and Plasmaforschung und Technologie (Greifswald).