Sleep and Light

admin — Fri, 10 Jul 2009 00:08:44 +0000

Light is one of the most important factors which has a direct influence on sleep. But before we can meaningfully understand the effects of light on sleep, we need to briefly discuss about the biological clock in our brain. As many of us are aware, almost all of our body functions and processes follow a cycle over a 24 hour period. The majority of these body function cycles are set on a central sleep/wake cycle. The sleep/wake cycle, then, crucially depends on stimuli in the form of light. Alternate light/dark periods are important for the proper “setting” and maintenance of the biological clock situated in the brain.
With this in the backdrop, let’s examine the effect of light on the sleep/wake cycle. Bright light, received by the retina of our eyes, is converted into electrical signals and relayed to the hypothalamus in the brain where the internal biological clock is located. This stimulates the breakdown of an enzyme in the brain which helps in the production of melatonin. Melatonin is the hormone that promotes sleep. As melatonin levels drop due to this sequence of biochemical events, sleep induction is withheld.
Alternatively, when there is low amount of bright light, the pineal gland in the brain secretes melatonin in several short bursts. This leads to sleep induction. During sleep, our closed eyelids make sure that visual stimuli in the form of bright light are prevented from entering the retina. This ensures proper melatonin levels and a good night’s sleep.
Exposure to bright light therefore plays a very important role in setting our internal biological clock and therefore in maintaining a healthy sleep/wake cycle. For this reason, some sleep clinicians and doctors say that it is highly beneficial if we can go outside early in the morning and get exposed to sunlight for a very short period of time. During this time strong visual signals are conveyed to the brain and this help it to set the biological clock.
Owing to the fact that exposure to light can greatly affect our sleep cycle, light therapy is now being tested out at many clinics to treat sleep disorders. Therapy using light is now also being used to help those suffering from acute jet lag recover more quickly. However, it must be stressed that it takes a few days for our body’s biological clock to reset itself to new light/dark patterns.
Given the importance of light in synchronizing the sleep/wake cycle, it is important to follow some basic guidelines to ensure a good night’s sleep. Firstly, it is highly recommended to turn off all lights during sleep. If this cannot be accomplished due to other reasons, then it is important to keep the light levels down to the minimum possible amount. The reason is that although our eyelids block out a significant portion of light, it cannot stop it completely. If the light intensity is high, then some part of it can penetrate the eyelids and cause the retina to give off impulses to the brain.
Another very interesting fact has emerged from a couple of recent studies. We have always believed that light can influence the brain (and hence sleep!) only by entering into the retina (eyes). However, there seems to be strong evidence to show that light shone on the back of the knee of s sleeping person can affect the quality of his sleep! Therefore, much more research is warranted on this interesting relationship between sleep and light.

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Sleep and Light