Blue Light and the Effect on Sleep

Original Editor - Kapil Narale

Top Contributors - Kapil Narale and Angeliki Chorti

What is Blue Light?

Blue light is a form of light that is released approximately between the wavelengths of 400 to 500 nm.

The most common source of blue light is sunlight. Blue light can also be emitted from electronic devices and digital screens, such as the television, computers, and smartphones, light-emitting diodes (LEDs), and fluorescent lighting. Some devices have become a permanent means of entertainment and communication, and are widely used in daily life. Blue light is emitted with a wavelength that may affect our circadian rhythm and thus can result in better ir poorer sleep. With the advent of digital health in patient and clinician lives, the increased use of technology and blue light may also be an issue in healthcare, and consequently, the urge to learn more about this topic is more prominent.

Nevertheless, blue light can also have beneficial effects as it can positively impact alertness, performance and wellbeing.

Benefits of Blue Light

Some benefits include:

• Increase in cognitive performance
• Increase in alertness
• Decrease in reaction time
• Increase in wellbeing

It is interesting to note that the increase in cognitive performance, alertness, wellbeing, and decrease in reaction time can aid in physical and sport performance, when relying on teamwork and decision making, and thus can promote injury prevention. In addition, exposure to blue light may improve depression symptoms, but efficacy and safety is still unproven.

Negative Effects of Blue Light

There are a range of negative effects that blue light can cause:

• Decrease in tiredness
• Decrease in sleep quality
• Decreased sleep duration
• Decreased sleep efficacy
• Increased time it takes to fall asleep

Factors like a decreased sleep quality and duration can have a negative effect on an athlete's physical and cognitive performance, as well as their recovery. It has been found by Tordjman et al (2017), that blue light halts the secretion of melatonin. The main role of melatonin is to regulate the circadian rhythm, the part of the body that effects sleep.

Studies have found that there was a decrease in individualised sleepiness with the exposure of blue light. A study found, as mentioned below, that there was a higher individualised sleepiness level with the use of blue light blocking glasses.

Physics of Blue-Light and The Effect on the Eyes

Light at wavelengths less than 380nm can not be seen by the eyes. However, a wavelength between 300 and 400 nm can transmit through the cornea, and be absorbed by the pupil or iris. Blue light of a wavelength between 415 nm and 455 nm (high energy short-wave) is the most harmful, and associated with eye light damage. When in the direction of the eyes, the high energy blue light transmits through the cornea and lens to the retina, which can cause diseases such as dry eye, cataract, and age-related macular degeneration. Direct transmission of the crystals into the retina would lead to an irreversible photochemical retinal damage. Due to these factors, prolonged exposure to blue light causes acceleration of fatigue in the eyes and nearsightedness.

Blue light can stimulate the brain, diminishing the secretion of melatonin, and improving adrenocortical hormone production, impacting hormonal balance and directly affecting sleep quality. This can decrease the excitability of the parasympathetic nerves, and decrease tear secretion, which can help lead to dry eyes. Similarly, sleeping disorders caused by blue light may be influenced by the aging (yellowing) of the lens and decreased transmission of blue light to the retina.

Effect on the Circadian Rhythm

Blue light may influence the circadian rhythm. Blue light activates the secretion of melatonin in the pineal gland. This can increase or decrease cortisol expression depending on the time of the day, and thus can control the circadian rhythm.

Sleep quality was seen to improve, in the elderly, after cataract surgery, since the transparent artificial crystal allowed more blue light to reach and transmit through the eye. Alertness, memory, and cognition may also be improved. However, if exposure to blue light is prolonged, especially before sleep when melatonin production is the highest, in addition to retinal damage through the ocular surface, it can also diminish the secretion of melatonin, increase the production of corticosteroids, and damage hormonal secretions, thus harming sleep quality.

Considering Conditions with Blue Light

Various studies, as outlined in the systematic review by Silvani et al (2022), consider the effect of blue light on sleep when compared to various light conditions:

• A study examined subjects performing tasks on a portable device before bedtime, with conditions of an iPad without blue-light blocking glasses vs. an iPad with blue-light blocking glasses, for 2 hours, which had a few findings. Sleep efficiency was significantly increased with the blue-light blocking glasses, time to fall asleep significantly decreased with the use of the blue-light blocking glasses, however sleepiness did not have a significant decrease in the blue-light condition.
• A study examined the use of Facebook before bedtime with the conditions of an iPad without a blue-light filter vs. an iPad with an amber filter, for 22.5 minutes, found that there was no significant change in sleep quality in the blue-light condition.
• A study examined watching a relaxing movie and completing reading tasks under the conditions of a blue-light computer screen vs. CCFL, for 5 hours, found that there was a significant individualised decrease in sleepiness in the blue-light condition.
• A study examined reading before bedtime with the conditions of using a tablet vs. a hard copy book, for 4 hours, and had a few findings. Evening sleepiness was significantly decreased in the blue-light condition, alertness in the morning was significantly dampened in the blue-light condition, sleep efficiency and total sleep duration had no significant change in the blue-light condition, and time to fall asleep was greater in the blue-light condition.
• A study examined sitting in the evening in conditions of blue-light vs. white-light, for 2 hours, and found that there was no significant decrease in wakefulness in the blue-light condition.
• A study examined performing tasks on a portable device during the daytime routine, using the conditions of tablets or smartphones vs. a hard copy book, for everyday use, and found that time to fall asleep significantly increased in the blue-light condition, and total sleep duration significantly decreased in the blue-light condition.
• A study examined reading before bedtime on an iPad vs. a hard copy book for 1 hour. Sleep duration and sleep efficiency had no significant negative change in the blue-light condition, and sleep quality had no significant decrease in the blue-light condition.
• A study examined reading before bedtime on an iPad vs. a hard copy book for 30 minutes. There was no significant difference in sleep duration or time to fall asleep between the blue light and non-blue0light conditions. Individualised sleepiness was significantly decreased in the blue-light condition.
• A study examining playing games before bed on an iPad vs. an iPad with a short wavelength filter, for 48 minutes, found that time to fall asleep, and individualised sleepiness showed no significant change between the blue-light conditions.
• A study examining smartphone use in the morning with the conditions of smartphone use vs. smartphone use with a display filter, for 150 minutes, found that there was a significant decrease in sleepiness in the blue-light condition.
• A study that examined office work and sitting during work hours, for 3 weeks, in a blue-light vs. white-light condition, found that sleepiness was significantly increased in the blue-light condition.
• A study examined elite athlete training with blue-light emitting activities during the hour before bedtime for 1 hour, found that time to fall asleep did not have a significant decrease with blue-light.

Please see table 3 in Silvani et al (2022) for a description of further studies that were analysed in this systematic review considering the effect of blue light on sleep.

Please see table 4 in Silvani et al (2022) on pg. 10-12 for an outline of studies considering the effect of blue light on performance, such as cognitive performance, alertness, reaction times, accuracy, daytime dysfunction, heart rate response, and handgrip strength.

Please see table 5 in Silvani et al (2022) on pg. 14 for an outline of studies considering the effect of blue light on wellbeing, consisting of mood, irritability, arousal, tension, anxiety, and motivation.

Blue Light and the Effect on Sleep Quality

As it is commonly known, the exposure to blue light decreases sleep quality. A good indication of sleep quality can be based on a measure of restful and good sleep. Sleep can be considered restful if there is minimal tiredness the next day, sleep efficacy is high, and if time to fall asleep is low. There are many factors that can contribute to sleep health, which include, tiredness, sleep duration, sleep efficacy, and time to fall asleep (sleep latency). Poor sleep quality results in bad sleep.

One study in Silvani et al (2022) noted that thee was a higher sleep quality in a non-blue light condition, and three studies reported that there was no significant different in sleep quality. There was one study showing an increase in sleep quality with blue light exposure. One of five studies showed an increase in sleep quality with blue light exposure, and one of five studies showed a decrease in sleep quality with blue light exposure. These results give a mixed an conflicting impression.

One study analysed in Silvani et al (2022) found that blue light did have a negative effect on sleep quality, while another study found that there was a positive effect on sleep quality. Three studies found that there was no significant change in sleep quality with our without blue light.

Blue Light and the Effect on Sleep Duration

Three studies included in Silvani et al (2022) showed that there was a decrease in sleep duration with the exposure to blue light, while one study indicated that there was an increase in sleep duration. Five studies showed that there was no significant difference in sleep duration.

Sleep Efficacy and Sleep Latency

It is interesting to note that in the systematic review by Silvani et al (2022), two studies reported that there was a higher sleep efficacy without the exposure to blue light, while two studies showed that there was no significant difference in sleep efficacy with exposure to blue-light. Only one study found that time to fall asleep was decreased with the non-blue-light condition. Two studies found an increase in time to fall asleep with the blue-light condition. Five studies found no significant difference in time to fall asleep between the blue-light and non-blue-light conditions.

Prevention strategies

Other than minimising the use of electronic devices before bedtime, certain devices can be used to help minimise the exposure to blue light. Devices such as a blue light glasses or a screen cover can be used.

Application to Athletes

The positive and negative factors from the exposure to blue light is a consideration to athletes, especially since good sleep hygiene is essential for a strong athletic performance. It is also a possibility that blue light may improve performance, especially since athletes may be in need of sleep as a result of their busy training schedules. With the increased use of electronic devices, the blue-light may impact sleep and lead to tiredness. Tiredness may be a factor impacting physical performance. There are instances where blue-light was seen to decrease tiredness, thus leaving the athletes with an option to decease their tiredness prior to competition. Since blue-light can help with improving physical performance, it can help with reducing injury and help with remaining focused. It is shown that 2 hours of exposure to blue/light can help reduce an athlete's tiredness.

It is seen that poor sleep quality results in 'bad sleep', thus decreasing an athletes' performance and recovery. These are very important factors for athletes as the performance and recovery will help lead them to success. A recommendation is to reduce blue-light exposure to 3 hours before bedtime, since it was found that athletes' performance decreased with this much blue-light exposure. An improvement in sleep quality can lead to an improvement in reaction time, accuracy, endurance performance, accompanied by a decrease in injury and illness. The athlete would need to make a decision of how they would like to decrease their blue-light exposure. This can also be done with the consultation of their coach. Minimising blue-light exposure for a limited number of hours may be sufficient during period of intense physical activity.

Sleep quality can have an impact on tiredness and one's perception of fatigue, as fatigue seems to be present with poor sleep quality. Thus, decreased level of tiredness would indicate good sleep quality.

It is seen that there may be a reduced sleep duration for athletes due to increased training, and tight schedules. Sleep duration may be even worse with the exposure to blue-light. Sleep duration would have less of an effect on overall fatigue, thus would be less important than sleep quality when considering optimal sleep habits.