Can certain types of light keep you awake at night? Obviously, too much light of any type WILL prevent you from falling asleep, but a little light from the streetlights outside, your television, or even your cell phone can also make it difficult to fall into a deep sleep.
This can result in waking up feeling groggy and tired, despite having "slept" for 7 or 8 hours straight! Let's look at the science behind light and sleep.
Science of Light & Sleep
Human beings have adapted their sleep cycles, or circadian rhythms, to the presence or absence of daylight. How does this work? The chemical melatonin regulates sleep. Melatonin is produced by the body when there is an absence of light entering the human eye. When daylight recedes, the body is naturally ready to sleep. In the morning, when daylight returns, the melatonin levels in the body are suppressed and a state of wakefulness resumes. This circadian rhythm worked great early in human history when only natural light sources existed.
Today, electric light is ubiquitous inside and outside homes. The result is often a disruption of the natural sleep cycles. It turns out that blue light (blue sky or 5000K and higher color temperature) is the primary driver for suppressing melatonin. Many light bulbs emit some blue wavelength light even if the appearance of the light is not blue. Much of the light emitted by electronic equipment use in the evening has a strong blue wavelength component.
Any blue light source can suppress melatonin and make going to sleep a challenge. At the extreme, for people who work night shifts or live in northern climates where a grey winter daytime sky limits blue light, there is a condition that some people develop called Seasonal Affective Disorder (SAD). With little exposure to daylight, blue light, or full-spectrum light, the broken sleep cycles can cause a severe medical condition.
Potential Sources of Late-Night Bright Light
Televisions, projectors, computers, laptops, tablets, and even cell phones can emit light in the 5000K spectrum or higher. If you use full spectrum light bulbs in your house or bedroom, you may also be giving your brain the signal to keep awake.
Are LED Street Lights Going to Eliminate Sleep Altogether?
One growing concern for many is the shift from sodium lights to LEDs in street lights. While low pressure sodium lamps are highly efficient sources of light, their yellow light makes them useful only for outdoor lighting. High pressure sodium bulbs utilize a broader spectrum of light, but their poor color rendering also limits their use.
LED street lights, on the other hand, can provide bright, white lights that can help drivers keep alert, aware, and awake when driving in the middle of the night. While beneficial for drivers at 2:00 AM, this could be a disaster for people whose bedrooms are anywhere near a street light powered by an LED.
Reducing the Risk
Thankfully, there are numerous ways to reduce the risk of poor sleep due to light exposure. The most obvious example may be to turn off the television and computer several hours before bed, and avoid using your cell phone as much as possible. Cell phones have turned into mini-computers these days, so either reduce the brightness of the screen or avoid using it entirely before bed.
In terms of the light bulbs in your house, consider using dimmer switches and appropriate lights. Not all light bulbs can be dimmed (although all incandescent and halogens can be). Look for dimmable CFL or LED lights if you are using energy efficient lighting throughout your home, and especially in your bedroom.
One innovative approach would be to use warm dimming LED lights, recently produced by at least one LED manufacturer. These lights can be dimmed to a lower color temperature with a dimmer switch, transitioning a room from a higher color temperature to a lower one.
Finally, remember to get enough daylight and blue light throughout the day! As the days get longer in spring and summer, enjoy the extra exposure to the bright light of the sun. If that is not possible because you work in a cave, consider full spectrum or daylight bulbs, or even neodymium bulbs that mimic daylight.
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