The proliferation of smart devices has led to an increase in exposure of digital screen time, with blue light having the largest negative impact on our sleep cycles. Conversely, green light has shown promising results in reducing migraine severity. Read on more to find out more about the effects of blue and green light.
What is blue light and green light?
Visible light is composed of an electromagnetic spectrum of different wavelengths and energy.
Blue light generates the largest signals in the retina and cortex while green light, generates the smallest signals. It has the most potential to cause harm to our eyes as compared to other visible light.
The sun is the primary source of blue light but artificial sources also include:
- Digital screens on smart devices
- Fluorescent lights
- LED lights
- Computer screens
How blue light affects vision
When light passes through, electrical signals are generated in the retina at the back of the eye and in the cortex region of the brain. Our retina is the most susceptible as high-energy visible blue light can pass through multiple eye structures to reach the light-sensitive retina at the back of our eyes.
Blue violet light is called high energy visible light (HEV) that resembles the sun’s damaging blue light. Artificial blue light from our smartphones, computers and devices are weaker than the sun and typical exposure levels from consumer digital screens do not increase risks of macular degeneration or blindness.
Although there is not enough evidence to prove that electronic blue light directly causes eye damage, it can contribute to other eye problems.
Research has shown that blue light can potentially damage the light-sensitive cells of our eyes. Since blue light scatters easily, poorly focused blue light reduces contrast, resulting in digital eye strain. This can include dry eyes and blurred vision.
Focusing on screens for too long may also trigger ocular migraines and headaches.
Children are unable to filter blue light as well as adults and excessive screen time may increase chances of developing myopia and attention focusing issues.
Why should we avoid blue light before we sleep?
Blue wavelengths boost attention and speed up reaction times. It alters core body temperature and heart rate, primary to our circadian rhythm. The Circadian rhythm is our body’s biological clock that regulates our daily essential functions. Sleep cycles are one of the types of known circadian rhythms.
Blue light impacts our circadian rhythm by improving our attention and performance in the day by stimulating part of the brain that keeps us alert. However, exposure to excessive blue light at night tricks our brain into entering daytime mode, which disrupts our body’s natural circadian rhythm, keeping us alert instead of preparing our body for rest.
Exposure to blue light for as little as two hours can suppress melatonin secretion. Melatonin is a hormone that regulates our sleep-wake cycles, by signalling the body to prepare for sleep. It also causes slower melatonin release in children, and parents are encouraged to limit their child’s screen time before bedtime.
Blue light also interacts with cortisol, a hormone that induces stress. Negative health impacts such as depression and metabolic orders such as obesity may result when chronic misalignment occurs.
How can we mitigate the effects of blue light?
The simplest way is to dim or turn off the above devices before bedtime. Creating a routine to remind one to reduce the use of electronic devices two hours before bed may help to improve sleep.
Blue light filters help to play an important role in reducing blue light exposure and can be conveniently installed on our smartphones, tablets and computers. Many smartphones also carry “night mode” that emit lesser amounts of blue light.
To help with eye strain, prescription glasses with photochromic lenses can offer protection from UV and blue light. These lenses darken in bright light to reduce glare.
Blue light glasses help reduce digital eye strain by deflecting blue light away with a special coating on the lens. Research has shown that wearing such glasses a few hours before bedtime can help one to fall asleep faster.
How does green light make people feel better?
On the other hand, green light helps to reset the circadian rhythm by regulating melatonin.
Green light stimulates the receptors of the endogenous opioid system, a pain-relieving system found in the immune, nervous and gastro-intestinal systems. This in turn, increases levels of serotonin production. Serotonin is a hormone that affects our emotions, motor skills and is a natural mood stabiliser. It regulates sleep, our eating habits and digestion.
Green light for migraine relief
Photophobia is a type of light sensitivity that affects nearly 15 percent of the world and is a symptom of migraine headaches. The majority of migraine sufferers experience worse migraines when exacerbated by light.
A Harvard study has shown that specific narrow bands of green light may reduce light sensitivity and headache severity.
Interestingly, research has shown that neurones in the thalamus, a part of the brain that transmits light information from the eye to the cortex, were stimulated the least by green light, as compared to blue and red light. This decrease in stimulation and responsiveness explains why green light is favoured by the migraine brain.
Although there is limited research about green light therapy at this point of time, one study conducted saw a three-fold increase in enkephalins, a molecule that acts as a natural pain reliever, when exposed to green light.
Blue light does not directly harm any part of the eye and the reduction of screen time before bed can help to improve our quality of sleep.
On the other hand, green light therapy may seem promising, but more research needs to be done. Migraine sufferers should speak to their doctors for alternative treatments that may benefit them.