What is Blue Light?

What is Blue Light?

Blue Light Glasses - What is blue light? 

Blue light is part of the visible spectrum. This spectrum is visible to the eye and consists of various wavelengths of differing sizes and energy levels. 

The blue light wavelengths are shorter high energy wavelengths and are the closest part of the visual spectrum to the high energy UV spectrum. 

The blue light wavelengths are in the range of 380 - 500nm (nanometers) 



Why is blue light harmful?

Blue light is not always harmful, in fact it is important that we are exposed to a certain amount of blue light on a daily basis which improves alertness, helps memory and boosts cognitive function and mood. 

When we spend time outdoors we generally get enough exposure to blue light to reap these benefits.  This is why in the winter time some people suffer from SAD (seasonal affective disorder) as they are not getting enough blue light exposure to gain the positive physiological effects.

Like all things in life, blue light exposure is all about balance and the danger comes from over-exposure to blue light. We tend to become overexposed from using digital screens such as PC’s, laptops, tablets and smartphones.

A recent study showed that, on average we are spending 3.5 hours a day on our smartphones and checking them 55 times a day in total. When you add all the other digital devices such as PC’s, tablets etc that we use on a daily basis it results in a very significant amount of exposure to blue light throughout the day.

Our optometrist Seamus has noticed a huge increase in the number of patients presenting to clinic suffering from digital eye strain particularly in the last 5-6 years. This coincides with a much higher usage of digital devices in the same time frame.

These digital screens emit high energy, high frequency blue light wavelengths which causes a stress on the visual system if we are exposed to 2 hours or more of screen-time a day.

To understand why this is, think of the damage that UV causes to the eye. Overexposure to UV results in the high energy UV wavelengths causing oxidative damage to the cells of the cornea and other eye structures. Blue light also has high energy wavelengths and are the closest wavelengths of the visual spectrum to UV light. Whilst it likely doesn’t cause significant damage to the eye structures like UV does it certainly has enough high energy to cause a stress on the visual system and lead to eyestrain and tired eyes in cases of over-exposure. A 2014 study in Investigative Ophthalmology and Visual Science journal, on blue light (1) concluded that “our results indicate that blue light with short wavelengths (410–480 nm) can induce oxidative damage to the corneal epithelium”


How does blue light exposure affect children?

Children have larger pupils than adults which mean more blue light can enter the eye and their crystalline lenses are not as fully developed as that of an adult so it cannot absorb as much blue light as an adult crystalline lens would resulting in more blue light getting through to the retina in the back of the eye.


How does blue light affect your sleep?

Melatonin is a sleep hormone that is produced by the pineal gland. It is secreted at night in a  rhythm called the circadian rhythm and is at a maximum level in the blood stream at around 3am. The rise in the level of melatonin correlates to an increase in sleep propensity.

Melatonin provides the body an internal signal for darkness which is how it helps us sleep. Sunlight entering the eye during the day prevents melatonin from being secreted and keeps us awake. When the eyes don’t get any exposure to sunlight in the evening/night melatonin begins to be produced. When we use digital devices before bedtime the blue light emitted has the same affect of sunlight during the day and inhibits the production of melatonin. This is because the blue light has shorter high energy wavelengths and is of sufficient strength and frequency to affect the pineal glands secretion of melatonin.



So, what can be done to protect our eyes from blue light?

If you are using a digital device for 2 hours or more a day it is a good idea to use blue light glasses to filter out the blue light. This prevents eyestrain, tired eyes and headaches and will help regulate the sleep cycle if you are using these devices in the evening or at night.

Blue light glasses work by filtering out blue light, absorbing or reflecting the blue light with multiple filter layers embedded in the lenses.

Limiting the time you spend looking at digital screens can be difficult especially as more and more of us are spending longer hours working and studying on screens but if possible it’s a good idea to limit the time spent as much as possible.

This is also true for kids and we have a blog post here where we give tips on how to keep screen time with kids to a minimum.

In order to prevent blue light disrupting your sleep cycle its best to avoid using screens late in the evening or at night or to wear blue light glasses when doing so.

We have a blog here with tips on this and other ways to ensure you get a good night’s sleep.





What evidence is there to support the use of blue light glasses?


A 2017 study (2) entitled Short-Wavelength Light-Blocking Eyeglasses Attenuate Symptoms of Eye Fatigue by Lin JB et al set out to investigate if wearing blue light blocking glasses whilst using digital screens experience less visual fatigue and report fewer symptoms of visual discomfort than control subjects who wear glasses with clear lenses.

The subjects performed a computer task lasting two hours and digital eye strain was measured objectively by measuring critical flicker fusion frequency.

The results of the study showed that the change in Critical fusion frequency after the computer task was significantly more positive (i.e., less eye fatigue) in those wearing blue light glasses versus those with no-block (P = 0.027) and low-block (P = 0.008) groups. Moreover, random assignment to the blue light glasses group but not to the low-block group predicted a more positive change in CFF (i.e., less eye fatigue) following the computer task (adjusted β = 2.310; P = 0.002). Additionally, those wearing blue light glasses reported significantly less feeling of pain around/inside the eye (P = 0.0063), less feeling that the eyes were heavy (P = 0.0189), and less feeling that the eyes were itchy (P = 0.0043) following the computer task, when compared to subjects not wearing blue light glasses.

Another 2017 study by Leung et al (3) set out to examine the benefits of blue light glasses. Their study, Blue-Light Filtering Spectacle Lenses: Optical and Clinical Performances showed that blue light blocking glasses lenses reduce phototoxicity by 10.6%–23.6%, without degrading visual performance, and have thus been suggested as an aid for protecting the eyes against the blue light hazard.

A 2016 study (4) published in Molecular Vision investigated the effects of blue light on eye physiology and on the circadian system. It shows that blue light in the range of 460–480 nm is more effective compared to monochromatic light of 555 nm in reducing the production of melatonin and thus phase-shifting the human circadian clock.                                      It also shows that there can be an accumulative effect of blue light exposure in the eye which can cause long terms concerns as well as the short term effects.

A 2020 study (5), published in the journal of applied physiology, on the effects of blue light glasses on sleep and productivity, entitled The effects of blue filtration on sleep and work outcomes by Cristiano Guarana and Christopher Barnes again showed significant improvements in sleep and work outcomes for those wearing blue light glasses versus a placebo group.  


(1) https://iovs.arvojournals.org/article.aspx?articleid=2128327

(2) https://pubmed.ncbi.nlm.nih.gov/28118668/

(3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5207664/

(4) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734149/

(5) https://pubmed.ncbi.nlm.nih.gov/32658494/