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Green Light: the Facts

by | Blue Light 101

If you’re a savvy, health-conscious person who is probably already using blue light blocking solutions, you’ve probably started to hear talk about green light. But what exactly is green light and do you need to block it? There are a number of companies selling you on the idea that you do. However, before you get caught up in the ‘green light’ hype, let’s have a look at the actual science.

Here at Swanwick, we’ve done all the hard work by researching the latest scientific evidence on green light. We develop products based on real science, to give you the best outcomes possible when it comes to your sleep, productivity and overall well being. We know you’re busy, so we’ve made it simple for you to make an informed decision by breaking it down for you in easy to understand terms.

 

What is Green Light?

Green light is a light wavelength on the visible light spectrum. It operates just above blue light on the spectrum, from around 500 nanometers(nm) to 565nm. 

You are probably already familiar with blue light, which operates between 380nm-500nm, sitting between ultraviolet light and green light on the spectrum. Just like blue light, green light is emitted from both the sun and artificial light sources such as light bulbs, cell phones, computer screens, TVs etc.

Effects of Green Light on Sleep

You’ve probably heard recently claims that when it comes to sleep, it is just as important to block green light as it is to block blue light. From numerous scientific studies, we already know that blue light, especially in wavelengths of 450-480nm, suppresses the body’s ability to naturally produce the sleep-promoting hormone, melatonin. This results in more difficulty falling asleep, staying asleep, and reduced sleep quality. But does this also apply to green light? The studies may surprise you.

We comprehensively scoured medical journals and scientific publications for research studies on the human response to green light, especially regarding the effects on sleep. We found a number of relevant independent studies which have, along with our own studies and testing, assisted us in the development of our products. For the benefit of your own research, we are sharing this research with you in this article.

 

Don’t have time to read everything?

We’ve provided a short summary of the research at the start of each section, followed by more of a deep dive into the research, so you can choose how much detail you need to know. Just skip to the sections in boxes if you want a summary of the information.

 

Blue light suppresses more melatonin than green light

The following  studies all compare the suppressing effects of different wavelengths of blue and green light on human melatonin production. The results across the board are consistent in showing that exposure to the blue light wavelengths had a greater impact in suppressing melatonin (up to 81% in one study), both in terms of percentage and duration of suppression. They also show that green light does have an effect on melatonin production, but to a much lesser extent, and mostly in the lower 500nm range closest to the blue light spectrum. One study also found that the suppressing effect of green light is temporary even under continued exposure, whereas blue light has an ongoing suppressing effect for the duration of exposure. This further cements the proposition that blue light is the main offender when it comes to sleep impacts.

Conclusion: Blue light is a far more significant factor in melatonin suppression than green light.


A study published by the New York Academy of Sciences showed that it is primarily blue light which had the most impact on suppressing natural melatonin production. The study found that subjects exposed to different wavelengths of monochromatic demonstrated the highest melatonin suppression of 64% at exposure to 509nm, followed by 26% suppression with 476nm, 20% suppression with 542nm, 16% suppression with 574nm, and no suppression with light at wavelengths of 448 nm or 604 nm.1

This indicates that blue light and the green light that is very close to the blue light spectrum, suppresses the highest percentage of melatonin production, ranging from 26-64%, whereas pure green light had only a 16-20% suppression rate. 

A later study led by the same researcher and published by the Journal of Clinical Endocrinology & Metabolism found that monochromatic light at 505 nm is approximately four times stronger than 555nm in suppressing melatonin in healthy humans.2

A third study conducted by Flinders University and published in Chronobiology International 3, found that nocturnal melatonin was suppressed more by medium to short wavelengths of light (i.e. blue light), with the greatest suppression at 495nm (blue light), followed by 525nm(green light) and 470nm (blue light) They found that blue light with a wavelength of 497, was able to suppress nocturnal melatonin production by nearly 81%. 

A fourth study published in Science Translational Medicine 4measured the effect of blue and green light on spectral sensitivity. They found that during exposure to blue light at 460nm, most subjects elicited a relatively constant amount of melatonin suppression, whereas exposure to green light at 555nm initially elicited a strong suppression of melatonin, but over time, those levels returned to baseline levels, even during continued exposure. They attribute this to cells in the eyes called melanopsin, which are particularly sensitive to blue light, and continue to communicate blue light exposure to the part of the brain that regulates the circadian rhythm. Green light on the other hand, does not trigger this response in melanopsin, which explains why the suppression of melatonin is only temporary when exposed to green light.

Another study published by Nature journal5 confirmed that melanopsin in the eye does not respond to narrowband (green) light stimulation at 540nm or higher, which is consistent with other studies on the role of melanopsin sensitivity to blue light only.

 

Green light as a stimulant

In comparing blue and green light, it is useful to not just study how these wavelengths suppress sleep processes, but also what opposite effects they promote in relation to wakefulness and cognitive brain activity.

The studies we researched all indicate that blue light is much more potent when it comes to promoting electrical activity in the brain, and increasing performance measures such as alertness, reaction time and attention levels. This is important to note because these are all opposite indicators to sleep, that is, it is unlikely that one will show high levels of alertness and certain brain activity, if sleepiness is also present.

Several studies also highlight discoveries in blue light’s impact on the cellular level (melanopsin), finding cognitive brain responses to blue light in visually blind people, which did not occur when exposed to green light wavelengths.

Conclusion: Blue light stimulates electrical activity in the brain in a way that green light does not.


Blue light increases alertness and lowers subjective sleepiness

A study published in SLEEP journal6 compared people’s performance and sleepiness exposed to blue light at 460nm or green light at 555nm during the day, to the same levels of exposure at night. The results showed across the board that blue light caused higher ratings in measures of alertness than green light.

The results showed daytime exposure to blue light at 460nm increased auditory reaction time, reduced attention lapses and increased EEG (electrical brain activity) correlates of alertness, as compared to green light exposure at 555nm. At night, blue light also resulted in lower attentional lapses and lower reaction times than green light. 

On the Karolinska Sleepiness Scale out of 9, subjective sleepiness was rated an average of 4.5  for those exposed to blue light at night, whereas this increased to an average rating of 6 for those exposed to green light at night. These results were also supported by an earlier study by some of the same researchers which elicited similar results when comparing exposure at the 460nm and 555nm range7.

Another article published by PLOS Biology Journal8 summarises a number of studies which indicate that blue light is more effective than green light at increasing alertness in humans. The article states that: “All studies converge to show that blue-enriched light is more efficient in increasing performance and decreasing sleepiness suggesting a primary mediation through melanopsin-based phototransduction,” and “[t]ranslated to humans, these results reinforce the idea that blue light exerts a powerful alerting effect compared to green light.” It goes on to summarize that “the effects are stronger with blue (460–480 nm) as opposed to green (555 nm) mono-chromatic light, in promoting alertness during both day and night, waking EEG, or task-related brain responses.”

Blue light increases brain activity

A study published by PLOS ONE Journal9 found that participants completing a memory exercise while exposed to blue light (474nm) showed increased activity in the left hippocampus, left thalamus, and right amygdala of the brain, as compared to those exposed to green light (527nm) or monochromatic violet light (430nm). These areas of the brain are responsible for motivation, emotion, learning, and memory.

 

Key takeaways from current studies

There has already been significant scientific research on the effects of blue light and green light in relation to sleep. From this data we can conclude that blue light is more significant in its impact on melatonin suppression, although green light at the lower wavelengths also demonstrated some impact on melatonin suppression to a lesser degree. We can also conclude that blue light has a stimulating effect on the brain, promoting functions associated with a wakeful state, such as cognitive brain activity, alertness and reactivity.

Without a doubt, these factors indicate that the blue light wavelength is the primary offender when it comes to impacting sleep processes. One of the reasons for this is that blue light is received by the brain on a cellular level via melanopsin cells in the eye, and these cells are specifically sensitive to blue light, rather than green light.

 

Do I need to block green light?

The short answer is, probably not given studies show very little added benefit, as well as some possible downsides. The proven effectiveness of the amber-tinted lenses in Swannies®, which in addition to blue light, block the majority of impactful green light up to 540nm provide effective protection and visual comfort.

You can choose to block the full green light spectrum, and there are glasses that promise to do this, but the trade-off is that you will need to wear much darker red lenses which may have a more significant impact on your visual experience than orange-tinted blue blockers. You’ll also be blocking the relaxing, mood-boosting benefits green light has been shown to offer.


While there is evidence that part of the green light spectrum has some impact on melatonin suppression, this is limited to the lower range of the green light spectrum closest to blue light, below 540nm.

There is a large body of evidence which indicates that blocking blue light alone is more than sufficient to combat the negative effects of artificial light on sleep. A recent study published by the Journal of Applied Psychology10, using Swannies® Blue Light Blocking Glasses showed that participants using Night Swannies in the evening slept up to 6% longer and improved sleep quality by up to 14%. Another study by SleepScore Labs™ showed that people who used Night Swannies® took an average 11 minutes less time to fall asleep, 24 less minutes awake during the night and a 14% increase in sleep quality. 

You can read more about these studies, as well as studies on the effectiveness of blue light blocking glasses by clicking here.

With Night Swannies® blocking over 99% of blue light at least 80% of green light up to 540nm, this provides more than sufficient light protection to optimize sleep.

 

The downsides to blocking green light

While blocking blue light appears to be a very sufficient measure to protect oneself from the negative effects of artificial light on sleep, why not also block all green light, just to be on the safe side?

Blocking 100% of green light could actually have a negative effect on your mood, making it harder to sleep. Green has been found to be the most relaxing color for humans. A study published by the University of Georgia11 which compared emotional responses to color found that the color green attained the highest number of positive emotions including the feeling of relaxation, happiness, comfort, peace and hope. All emotions which are conducive to sleep.

There is yet to be a study which directly compares glasses that block the full blue and green light spectrum, vs those which only block blue light and partial green light spectrum. However, in order to block the full green light spectrum, a much darker and redder lens is required, as compared to blue blockers such as Swannies® which have an amber tinted lens. The problem with the darker red lens, is it is much more intrusive to your visual experience, and can be more difficult to get used to than an orange lens, which does not significantly darken the scope of vision.

Red lens glasses

Amber-lens Night Swannies

 

Glossary of Terms

EEG
An electroencephalogram (EEG) is a test used to evaluate the electrical activity in the brain. Brain cells communicate with each other through electrical impulses.

Melatonin
A sleep-promoting hormone released by the pineal gland, which helps regulate the body’s sleep-wake cycle. 

Melanopsin
Cells found in the retina of the eye which are particularly sensitive to the absorption of short-wavelength blue light. Melanopsin communicates directly with the part of the brain known as the ‘central body clock’ and plays a role in regulating circadian rhythm.

 

References

1Brainard, G.C.; Lewy, A.J.; Menaker, M.; Fredrickson, R.H.;. Miller, L.S.; Weleber, R.G.; Cassone, V.; Hudson, D. Effect of Light Wavelength on the Suppression of Nocturnal Plasma Melatonin in Normal Volunteers.

2G C Brainard, J P Hanifin, M D Rollag, J Greeson, B Byrne, G Glickman, E Gerner, B Sanford. Human melatonin regulation is not mediated by the three cone photopic visual system.

3Helen R. Wright and Leon C. Lack. EFFECT OF LIGHT WAVELENGTH ON SUPPRESSION AND PHASE DELAY OF THE MELATONIN RHYTHM.

4Joshua J Gooley, Shantha M Rajaratnam, George C Brainard, Richard E Kronauer, Charles A Czeisler, and Steven W Lockley. Spectral responses of the human circadian system depend on the irradiance and duration

5Z Melyan, E E Tarttelin, J Bellingham, R J Lucas, M W Hankins. Addition of human melanopsin renders mammalian cells photoresponsive.

6Shadab A. Rahman, PhD, Erin E. Flynn-Evans, PhD, Daniel Aeschbach, PhD, George C. Brainard, PhD, Charles A. Czeisler, MD, PhD, Steven W. Lockley, PhD. Diurnal Spectral Sensitivity of the Acute Alerting Effects of Light

7Steven W Lockley, Erin E Evans, Frank A J L Scheer, George C Brainard, Charles A Czeisler, Daniel Aeschbach. Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans

8Patrice Bourgin, Jeffrey Hubbard. Alerting or Somnogenic Light: Pick Your Color

9Gilles Vandewalle, Christina Schmidt, Geneviève Albouy, Virginie Sterpenich, Annabelle Darsaud, Géraldine Rauchs, Pierre-Yves Berken, Evelyne Balteau, Christian Degueldre, André Luxen, Pierre Maquet , Derk-Jan Dijk. Brain Responses to Violet, Blue, and Green Monochromatic Light Exposures in Humans: Prominent Role of Blue Light and the Brainstem

10Guarana, Cristiano L. Barnes, Christopher M. Ong, Wei Jee. The effects of blue-light filtration on sleep and work outcomes

11Naz KAYA and Helen H. EPPS. Color-emotion associations: Past experience and personal preference