sleep can be disrupted by dyssomnia insomnia hypersomnia narcolepsy sleep apnea parasomnia sleepwalking rem behavior disorder bruxism and circadian rhythm sleep disorders
light therapy utilizes bright light exposure to induce phase advances and delays in sleep and wake times
 although chronotype varies from individual to individual as determined by rhythmic expression of clock genes people with typical circadian clock function will be able to entrain to environmental cues