Note: This article is not intended as medical advice. One
should always consult with a doctor when considering light therapy.
An Estimated 35 million Americans suffer from Seasonal Affective Disorder
(SAD). Most scientists believe that SAD and other mood and sleep disorders
are associated with shifted circadian rhythms (i.e. body clock). Those
with ‘weak’ circadian rhythms need a very bright stimulus of light to
reset their body clock each day. When they don’t receive this light
signal, their body clocks either speed up (Advance) or slow down (Delay).
This “Out of Whack,” body clock then produces the wrong hormones at
the wrong time of day, causing the symptoms of SAD and other mood and
sleep disorders. This article attempts to explain how bright light can
re-shift delayed and advanced circadian rhythms back to their normal
DELAYED SLEEP PHASE SYNDROME
The vast majority of people have no problem with sleep/wake cycles,
but about 7% have a weak circadian system. Of this group, 80% will suffer
2001 Apollo Light Systems, Inc.
Sleep Phase Syndrome (DSPS), and need a very strong stimulus of bright
light to reset their internal clocks each day. When they don’t get this
stimulus, their body clock will migrate to a later time of day until
it receives a strong enough stimulus of light.
treatment of sleep disorders is based
on the hypothesis that the body's internal clock
will only respond to bright light
at a certain time of day.
Most people with sleep disorders fall into this category.
They hate to get up in the morning, have a terrible time at school or
work, and usually have trouble falling asleep until 2:00 or 3:00 in
the morning. Their subjective morning has probably migrated to 12:00
p.m. or even later.
‘Peak Time’ Corresponds to Minimum Core Body Temperature
The treatment of sleep disorders with light therapy is based on the
hypothesis that the body’s internal clock will only respond to bright
light at a certain time of day. This ‘peak time’ for people with normal
circadian rhythms occurs when they are in R.E.M. sleep, approximately
1 to 2 hours before awakening. Sleep labs can determine this peak time
by one’s body temperature. When the body temperature drops almost a
full degree, the pineal gland in the brain is most receptive to light.
Light received just prior to this ‘peak time’ will delay the circadian
rhythm and push the body clock forward, causing the person to wake up
later, while light received just after will advance the circadian rhythm,
causing the person to wake up earlier.
Normal circadian rhythm (waking
time: 7:00 a.m.) Body temperature minimum usually occurs 1-2 hours before