The internal mechanisms that affect and play an important role in our endless cycles of sleep and wakefulness make up an amazing system. However, a variety of internal and external factors can greatly influence the balance of this sleep-wake system.
|Age and condition||Sleep Needs|
|Newborns (0–2 months)||16 to 18 hours|
|Infants (3–11 months)||14 to 15 hours|
|Toddlers (1–3 years)||12 to 14 hours|
|Preschoolers (3–5 years)||11 to 13 hours|
|School-age children (5–10 years)||10 to 11 hours|
|Adolescents (10–17 years)||8.5 to 9.25 hours|
|Adults, including elderly||7 to 9 hours|
During a person’s lifespan, the amount of time we spend sleeping each day reduces. Newborns spend about 16 to 20 hours asleep every day. Between the ages of one and four, total sleep time per day reduces to about 12 or 14 hours. This gradual decline in sleep continues throughout childhood, such that an adolescent will need, though not actually get around nine hours of sleep to function at their best. Middle aged adults need about eight hours, and while the elderly still require about eight hours of sleep, they may struggle to obtain those hours at one stretch.
Other factors that affect sleep include medical conditions and stress, especially those that cause chronic pain and discomfort. External factors, such as what we eat and drink, medications and the environment in which we sleep can also greatly affect the quantity and quality of sleep. In general, all these factors are likely to increase the number of awakenings and limit the depth of sleep.
Effect of Light
Light is one of the most important factors that can affect and disrupt sleep. It does so both directly, by making it difficult for people to fall asleep, and indirectly, by affecting the timing of the internal clock and thereby affecting our desired time to sleep. Light affects our internal biological clock by means of specialized light-sensitive cells in the retina of our eyes. These cells inform the brain if it is day or night and our sleep patterns are set accordingly.
As a result of invention of the electric light bulb in the late 19th century, we are now subjected to much more light at night than we had been exposed during in the initial stages of evolution. This new pattern of light exposure has certainly affected our patterns of sleep. Exposure to light in the evening causes a delay in the phase of our internal clock and leads us to prefer later sleep times. Exposure to light at night during bedtime can have negative effects, but can certainly be enough to cause our internal clock to be reset, and can make it tough to fall back to sleep.