Changes

Before the advent of electrical lighting in modern times, humans historically had a stable time during the night in which there is little light. This helped stabilise their circadian rhythms and kept them synced to the natural day/night cycle.

Before the advent of electrical lighting in modern times, humans historically had a stable time during the night in which there is little light. This helped stabilise their circadian rhythms and kept them synced to the natural day/night cycle.

Modern humans often use electric lighting during the night. This can cause difficulty sleeping, as the body thinks it is still daytime even if it is already midnight, and is the reason why people often experience the desire to sleep later and later each day. For monophasic sleepers, a relatively stable, albeit short, dark period can be maintained during their sleep hours, which prevents their body clocks from going totally haywire.

Modern humans often use electric lighting during the night. This can cause difficulty sleeping, as the body thinks it is still daytime even if it is already midnight, and is the reason why people often experience the desire to sleep later and later each day. For monophasic sleepers, a somewhat short dark period can be maintained during their sleep hours, which keeps their circadian rhythms relatively stable.

However, for polyphasic sleepers who might not have such long sleep blocks, this poses an issue. As light is present around the clock, melatonin production is suppressed and the quality of SWS is compromised. This causes extra difficulty in adaptation and is also unhealthy. To avoid this, polyphasic sleepers (and monophasic sleepers too, for extra benefits) should practice a dark period, during which no blue and green light should enter the eye.

However, for polyphasic sleepers who might not have such long sleep blocks, this poses an issue. As artificial light is present around the clock, melatonin production is suppressed and the quality of SWS is compromised. This causes extra difficulty in adaptation and is also unhealthy. To avoid this, polyphasic sleepers (and monophasic sleepers too, for extra benefits) should practice a dark period, during which no blue and green light should enter the eye.

== Mechanism ==

== Mechanism ==