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Shift direction is determined by the choice of light exposure range:
. Exposure to light in the evening or during the first part of the night (before 5am) delays the melatonin secretion phase. 

 

 
 
 
. Exposure to light in the second part of the night (after 5am) advances the melatonin secretion phase.

 

 

 
. These shifts in the biological clock (delay and advance) can be attained using a light intensity of around 2500 lux. 

. The sun's intensity at midday reaches around 100000 lux. 
 

. Light intensity of a bedside lamp varies between 50 and 200 lux.

 
6.6.3.2.2. Light application 

 

Example 1: westward flight or night work
Bedtime delayed 7 hours with regard to biological clock phase
Results show the following after three lighting cycles between 2am and 5am at 2500-3000 lux:
 
. The biological clock adjusts completely to the new sleep times: melatonin secretion peak is moved from 5am to 12am. 

 

 
. Daytime sleep under these conditions is of the same quantity and quality as reference nocturnal sleep with perfect adequacy for each sleep stage.

 

 
. Cognitive performance improves during the night. A complete inversion of the performance rhythm is observed with regard to the reference normally observed at night.

 

 
 
Example 2: return to Europe from the US after a long layover or after a long series of night shifts
Bedtime is advanced by 7 hours with regard to biological clock phase
Three lighting cycles between 10am and 1am are able to advance the biological clock by some 5 hours. The remaining shift (2 hours) is related to the intrinsic difficulty of moving the biological clock phase forward.
Upon return to Europe from the US, it is good practice to schedule rest periods at least equal to those of the layovers and not set off again immediately eastwards.
 

 
 
Time periods favouring exposure to light during and after a long layover
 
 
Time slots are given in base time.
Exposure to light for three hours either continuously or discontinuously (e.g. by periods of 30 minutes) shows similar beneficial effects.
During layover following a westward flight (for example towards the US), exposure to light between 8pm and 5am.
During layover after an eastward flight (for example towards Asia), exposure to light between 5am and 10am.
Upon return to Europe after a long stay in the US, exposure to light between 10am and 3pm.
Upon return to Europe after a long stay in Asia, exposure to light between 1pm and 12pm.
 
 

 
 
 
 
　
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本文鏈接地址：Getting to grips with Fatigue & Alertness Management(67)