Nighttime blue light exposure can derange the circadian rhythm. It may be a culprit behind many modern chronic health issues, including obesity, metabolic syndrome, and cancer. On the other hand, blue light exposure during the day is very beneficial. Read this post to learn how to hack your blue light exposure for your benefit.
What Is Blue Light?
Light is electromagnetic radiation of a variety of wavelengths within the electromagnetic spectrum.
There is both visible and non-visible light. Non-visible light includes ultraviolet ( UV ) and infrared light, while visible light includes the whole spectrum of the rainbow, including blue light. Within the visible light spectrum, each wavelength is represented by a color.
Of all the colors of the visible light spectrum, blue light (wavelength 446-477 nm) has the strongest impact on physiology and the circadian rhythm because our pigments react to this wavelength [ 1 , 2 , 3 ].
Humans have evolved to rise with the sun and go to sleep after sunset. Before the advent of technology, humans only used sources that emitted yellow, orange, and red light, such as fire, candles, and lamps. These lights have much less impact on our circadian rhythm and sleep-wake cycles than blue light [ 4 , 5 ].
Nowadays, advances in lighting and other technologies like television, computers, and digital clocks among others, have introduced more blue-white light to our environment. In addition, these lights are available at all hours, which can affect our health and wellbeing [ 5 ].
The higher-efficiency “green” light bulbs are not necessarily as beneficial for humans as they supposedly are for the Earth. Compact fluorescent light (CFL) bulbs contain about 25% of blue light, while this percentage reaches 35% in LEDs [ 5 ].
Generally, blue light is beneficial during the day, but harmful at night. What Are the Physiological Effects of Blue Light?
Light exposure anchors human body functions to the rise and fall of the sun. When sunlight, which contains blue light, hits the retina, the photoreceptor cells transmit nerve impulses to the hypothalamus . The hypothalamus is the command central for hunger , thirst, temperature regulation, hormone secretion, and sleep patterns, which fluctuate according to our circadian rhythm [ 6 ]. Photoreceptor cells in the retina of the eye (retinal cells, rod and cone cells). The arrangement of retinal cells is shown in a cross-section.
When light hits the eye, it hits the retina. This light-sensitive tissue is actually considered part of the central nervous system (CNS) and is connected to the brain via the optic nerve. There are several layers of nerve cells in the retina, but the ones that are sensitive to light are those with photoreceptor cells. Rods and cones are the light-sensing cells that allow us to see, while the retinal ganglion cells are important for circadian rhythm entrainment [ 7 ].
The suprachiasmatic nucleus (SCN) in the hypothalamus coordinates light exposure with bodily functions through hormonal, autonomic (involuntary nerve impulses), and feeding-related cues [ 7 ]. Source: [ 8 ] 1) Potential Negative Effects of Blue Light Exposure During the Night
The following adverse effects are commonly associated with increased exposure to blue night during the night. Note, however, that the majority of studies covered in this section deal with associations only, which means that a cause-and-effect relationship hasn’t been established. Other environmental and genetic factors may play a more important role. 1) Disrupting Circadian Rhythm
Normally, darkness at night allows a normal output of melatonin between 2:00 and 4:00 am. Then, bright daylight follows resetting the clock and beginning a new 24-hour day [ 9 ].
Intrinsically photosensitive retinal ganglion cells contain melanopsin (a light sensor protein), whose job is to synchronize the body’s circadian clock to light [ 10 ].
Exposure to blue light at night signals the body that it is daytime , consequently, messing up the circadian rhythm, which is crucial to many body processes. To entrain the circadian rhythm , it is important to both get sunlight in the morning and avoid artificial light at night [ 11 ]. 1) May Lower Melatonin Production
Melatonin is an important hormone that controls the sleep-wake cycle. Light at night, especially blue light , suppresses melatonin production [ 12 , 9 , 13 ].
Even dim light can interfere with a person’s circadian rhythm and melatonin secretion. A mere 8 lux (2x the brightness of a night light) can inhibit melatonin. The brighter the light and the longer the exposure time, the less melatonin the eye cells produce [ 14 , 15 ].
A theoretical model of different types of light and exposures indicates the following time needed for melatonin suppression [ 16 ]: Monochromatic red light at 100 lux , a reasonable living room lighting level, would take 403 hours of exposure to suppress melatonin by 50%
Candle: 66 min suppresses melatonin by 50%
60-watt incandescent bulb : 39 min suppresses melatonin by 50%
58-watt deluxe daylight fluorescent light: 15 min suppresses melatonin by 50%
Pure white high-output LED : 13 min suppresses melatonin by 50%
The extent to which light at night suppresses melatonin depends on both the wavelength (blue being the worst) and the intensity of the light [ 13 , 9 ].
For example, after 1 hr of light at midnight, melatonin could be suppressed up to 71% , 67%, 44%, 38%, and 16% with intensities of 3,000, 1,000, 500, 350, and 200 lux, respectively [ 17 ].
Melatonin levels are reduced most with dilated pupils exposed to 90 min of monochromatic blue light from 2:00 to 3:30 AM at a brightness of 0.1 lux, which is equivalent to the light of a full moon [ 9 ]. Blue light, even at a dim, moonlight level (0.1 lux), suppressed melatonin production more than any other wavelength in a study in rats [ 9 ]. People with light-colored eyes (blue or green, for example) are more susceptible to melatonin suppression by blue light than those with darker eyes [ 18 ]. 2) May Raise Cortisol Exposure to either […]