How Light plays a role.
United Airlines Boeing 747-400 SYD Li Pang
Jet Lag Therapy
"The judicious use of light (therapy and/or sunlight) at the appropriate time can quickly rebalance erratic circadian rhythm and speed recovery from jet lag. (Boulos et al., 1995; Wever, 1985; Dollins et al., 1994; Revell et al., 2006; Canton and Roberts, 2006; Paul et al., 2009). Jet lag treatment is especially effective when used in conjunction with exogenous melatonin (Arendt, 1997; Arendt et al.,1999; Revell et al., 2006). Melatonin, the body's natural endogenous sleep aid, is a tryptophan metabolite synthesized from serotonin by N-acetyl transferase (NAT) in the dark (Moore and Klein, 1974). In the presence of visible light, NAT is inhibited and melatonin production is shut down. Under normal circadian conditions, there is a small peak of melatonin production every afternoon at about 4 pm, and a much larger peak that occurs later in the evening between approximately 10 pm and 3 am. This pathway can be modified by a combination of light and exogenous melatonin treatment.
Internal melatonin can be enhanced by taking melatonin pills (0.5 mg is sufficient to fill all melatonin receptors associated with circadian imbalance) (Zhdanova et al., 1995), or by increasing its natural production by changes in the diet (Wurtman et al., 2003). Consuming foods that contain protein high in tryptophan, i.e., milk, especially together with sweets (increased insulin helps transport tryptophan across the blood-brain barrier), will naturally increase melatonin production and produce drowsiness. In contrast, high-protein food, such as meat that is rich in tyrosine and low in carbohydrates, can increase excitatory neurotransmitters and enhance wakefulness (Wurtman et al., 2003; Canton and Roberts, 2006).
In summary, by judicious exposure to daylight or circadian blue light and with careful timing of meals and intake of a low dose of melatonin, it is possible to resynchronize circadian rhythms and reduce symptoms of jet lag. (Brown, 1994; Arendt, 1997; Arendt et al., 1999; Eastman et al., 2005; Roberts, 2001b; Revell et al., 2006; Wurtman et al., 2003). " 
1. Circadian Rhythm and Human Health Joan E. Roberts http://photobiology.info/Roberts-CR.html