The Truth of Blue Light


The Truth of Blue Light

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Digital devices and the blue light that comes with has now become the centre of our lives. Almost everyone carries it in their pockets as an essential when leaving the home. They are used to answer all your important emails at work. Children use them as a means of learning for school. For the entire family, it acts as a medium for entertainment as well.

Combined with the increase in digital devices is a surge in health awareness and prevention of disease. We smoke less1. One in two adults are physically active2. Personally, I have become more conscious about diet, exercise and sleep. We are aware of Ultraviolet (UV) exposure on a sunny day and how we are encouraged to use a sunhat, sunglasses and sunscreen3.

Combining the two, there is raised concern about blue light emitted from these devices causing permanent damage to the eyes.

Before any alarm bells are raised about the mention of ‘permanent damage’. I want to cover some important topics before we start a campaign to purge blue light

We will look into

  • the definition of light, especially blue light, 
  • if it causes harm and how it can affect health,
  • and what we can do about it

As a disclaimer, if you have any eye problems, please see your local Optometrist. I may be an Optometrist but I am not your Optometrist. Building a relationship with your local Optometrist and having regular full eye examinations is paramount for maintaining good eye health.

What is Light and Blue Light?

Before I continue, I’d suggest trying to read and understand the following but if science, equations and explanations if not for you, feel free to skip this.

Light or more formally, visible light, is a form of electromagnetic radiation. Electromagnetic radiation is energy in the form of waves passing through an electric and magnetic field that surrounds us, similar to waves travelling through the ocean.

The electromagnetic spectrum describes the different types of electromagnetic radiation based on a specific property, wavelength, λ (represented with a lowercase Greek letter called Lamba and measured in metres).

This spectrum includes radio waves that allow the voice of your favourite radio hosts to be heard from the comfort of your car. X-rays are another type of radiation that allows doctors to see the bones of a fracture without cutting open the skin. Microwaves are a type of radiation where the wavelength is a specific distance to cause water molecules to vibrate allowing reheating of food.

Visible light is a form of radiation as well. It is particularly important as this is what our eyes can perceive and what we will focus on today.

As said before, the difference between all these types of radiations is the wavelength, which is determined by the frequency, f (measured in hertz) of its source and the velocity, v (speed in a certain direction and measured in metres per second; c is used in place of v to represent speed of light in a vacuum).

Furthermore, the velocity of the radiation is determined by the medium in which it travels in (e.g. air or water or glass)

We can describe the relationship between wavelength, frequency and velocity with one simple equation.

The Truth of Blue Light
The equation to show the relationship between frequency and velocity

Different colours of light have different wavelengths when observed as shown below. For example, blue light has a shorter wavelength than red light.

The Truth of Blue Light
Diagram showing the difference in wavelengths

How do we determine different colours of light

The retina is a layer of cells at the back of the eye which sense light. The specific cells that determine colour are called cones.

There are three different types of cones – short (S), medium (M) and long (L) – and they are all excited maximally by a particular wavelength of light – blue 420–440 nm, green 530–540 nm, and red 560–580 nm – respectively4

Different excitation levels for all three cones are observed for different wavelengths of light. For example, blue light will excite the cones sensitive to blue light while the other two cones would have no excitation.

Magenta, which is an additive combination of red and blue5, resulting in excitation of cones specified for blue and red equally. A more ‘bluish-magenta’ will excite the blue cones a little more, allowing for discrimination of colour

In the case of red-green colourblindness (formally red-green colour deficiency), one of the three cones, particularly the L or M cone (red or green detector) are missing or defective. This does not lead to complete loss of colour vision but an inability to determine as many colours (particularly shades of reds and greens) compared to an individual without colour deficiency

Males are more likely to have red-green colour deficiency due to the gene coding for the retinal long and medium cone being present on the X-chromosome. Males only have one X-chromosome so if there is one defective gene, this results in a defective L or M cone as opposed to females who have two X-chromosomes and must have both defective genes present on both chromosomes, which is significantly rarer6

Electromagnetic radiation outside of this visible light spectrum (380 to 740 nm) like UV light or infrared light do not excite the cones in the human eye and therefore are not perceived visibly.

Electromagnetic waves show a wave-particle duality7. This means that under certain conditions light, for example, can act as both a wave and a particle.

Around the turn of the 19th century, an interesting observation was made. When UV light was shone on a metallic surface, an electrical current was observed. Energy is neither created nor destroyed so the light was being transferred into electrical energy – hence, the Photoelectric effect8

It was noted that only above a certain frequency, an electrical current would be observed and if the UV light was below this particular frequency increasing the light intensity did not result in a current

In 1905, Einstein determined the reason for this is because light energy is packaged into quanta, called photons

Photons are massless packets of energy. The amount of energy, E  is determined by the frequency, f of the radiation.

The Truth of Blue Light
The equation to show the energy of a photon and how it relates to frequency

Planck’s constant is known as h. The higher the frequency, the photon will have more energy. For example, high-frequency gamma rays will have more energy per photon for low-frequency radio waves

For a high enough frequency, the photon will have enough energy when it is absorbed by an electron on the metal surface to cause this electron to escape. This leads to a flow of charge and thus a current

In the case of visible light, blue light has the shorter wavelength and thus a higher frequency as opposed to red light, which has the longest wavelength and a lower frequency of visible light.

Therefore, blue light has higher energy photons than red light.

A bit confusing with equations and science? Don’t worry, just remember blue light has more energy than red light. More energy has the potential to cause more damage.

UV light

We know that UV light is harmful especially when it causes skin cancers but it is also beneficial due to aiding in production of vitamin D in the body9

UV light is classed into three categories based on wavelength: UV-A (315-400 nm), UV-B (280-315 nm), UV-C (100-280 nm). Note that UV light has shorter wavelengths than visible light and so has more energy as well per photon

UV-C and 90% of UV-B is absorbed by the ozone layer and atmosphere10

This means the remaining UV that we are exposed to is mainly UV-A with some UV-B. The cornea (front transparent layer of the eye) absorbs some UV-B light. The lens absorbs the rest of the UV-B and UV-A light. This means little to no UV reaches the retina

Even though UV may not harm the retina, long-term UV exposure can result in cataract (clouding of the lens) and pterygium (growing on the whites of eyes towards the cornea)

Short term UV exposure, such as skiing for example, can result in photokeratitis, which is equivalent to sunburn but at the level of your cornea. The symptoms of pain are usually delayed. So you might have been fine while skiing, but the pain comes along a bit later

Therefore, it is important to use sun protection such as high-wrap sunglasses and sun hats to reduce UV exposure to the eyes. It is paramount that the sunglasses are rated “UV400” – these are rated to block UV light, not just offer a tint to reduce visible light11.

Our Digital Devices

Now that we have established the properties of light and its colours; let’s have a look at the white light

White light results for all colours being present if they are additive. This provides equal stimulation of all the three types of cone cells in our eye, giving the perception of white.

Most of our digital devices are backlit with light emitting diodes (LEDs). Digital devices include: modern televisions, computer monitors, smartphone LED and evening lights at home. LEDs, as a source of light, emits more blue light12 than for example an the old incandescent bulb13

You might notice that a LED light appears more blue compared to a candle light which is a bit more orange in colour. The amount of blue or orange is described as colour temperature, measured in Kelvin, K. Not to be confused with the thermal temperature which is also measured in Kelvin as well as degrees Celsius and Fahrenheit

Not all white lights are made equal. It results from the inconsistencies of all the different colours of light not being equal. Higher colour temperatures tend to be more blue (e.g. LED) and lower colour temperatures tend to have more orange (e.g. candle light)

We have established that blue light has higher energy and higher energy has more potential for damage. We now know that LED lights, which are used to backlight digital devices, have plenty of blue light

We can also now see the fear in blue light especially with digital devices and how our society has really moulded its way around use of these devices for work and entertainment

But does blue light really cause damage to the back of the eye?

Damage caused by Blue Light

From what has been discussed with blue light having higher energy and with so many people being exposed to this blue light from their digital devices, in theory, there should be damage to the retina

How does theory come into practice

A study was performed on mice, where one group who were exposed to cold fluorescent lamp developed more toxic products at the level of the retina than mice who were exposed to light with less blue light14

However, these mice were albino, which means they lacked pigment in the eye. The pigment is important to absorb excess light, reducing the damaging effects to the retinal cells

Also, the mice were exposed to a bright light for 7 days with no breaks. The human eye would require greater exposure than a mouse eye to get equivalent damage

I have good news for you

A light so powerful is not available for consumer use, so the study does not simulate real life.

It is very unlikely you will be in a position where you have this much exposure when using your laptop for gaming sessions with the boys, or girls. The amount of blue light from digital devices is well below the threshold that causes retinal damage to your eyes.

In fact, the biggest source of blue light is the Sun in the daytime15

But what about the Sun

The main culprit of the Sun is UV light, which is what we established before. We are doing most we can by wearing sunglasses. 

However, not much is known about blue light and the effects from the Sun

Macular degeneration (MD) comes into question when we talk about damage to the retina. MD is progressive loss and damaged or retinal cells particularly those responsible for high detail, central vision. This area is known as the macula. A person with macular degeneration would have difficulty discerning detail of letters of words on street signs even with their glasses and much worse cases would have difficulty recognising faces of friends and family

Still, the recommendation is to be a non-smoker, exercise and have a balanced diet focusing on fish, dark green vegetables, and nuts in order to reduce the onset and progression of MD.

Avoiding blue light from digital devices does not come into the equation.

What about blue light and eye discomfort

It is thought that blue light from the smartphone or the monitor contributes to eye discomfort. But this simply is not the case

With prolonged use of monitors, the rate of blinking reduces16. Regular blinking is important to spread moisture over the front surface of the eye. When the blink rate reduces, this layer of moisture (also known as the tear film) can evaporate and result in Dry Eye.

The main symptoms of Dry Eye is stinging or burning sensation of the eyes and this results from reduced blink rate when concentrating on your digital device, not blue light from the screen

Dry Eye can be alleviated with artificial tears recommended by your Optometrist. It is also important to stay hydrated as well17

In addition to this, constant focusing can lead to the eyes spasming. This is caused by, well, constant focusing with no breaks and once again not blue light

A good rule around this is to take breaks.

Implementing the 20/20/20 rule is useful in this case. For every 20 minutes of work, look 20 metres away for 20 seconds.

Make sure you see your Optometrist for proper management of your focus and your dry eye.

Sleep and Blue Light

So far we know blue light from digital devices is not harmful to the retina despite our previous theories. But what about sleep

Our body has an internal clock that produces a Circadian Rhythm, which is a physical or behaviour change that follows a 24-hour cycle

This could be apetite, body temperature and alertness, but an important to this topic is the sleep-wake cycle18

The sleep-wake cycle is strongly influenced by the hormone called melatonin. High levels of melatonin signal to our brain that it is time for sleep, hence, feeling drowsy; low levels signal the body to wake and feel refreshed after a good night’s rest

Melatonin is constantly produced in the pineal gland located deep in the brain

Light, particularly light on the blue end of the spectrum, acts as a cue for the sleep-wake cycle by signalling to the pineal gland to halt production of melatonin – the messenger of sleep19

The pathway for this: the retina receives blue light and this signals to the lateral geniculate nucleus (LGN), which in turn signals to the suprachiasmatic nucleus (SCN) to communicate with the pineal gland20 to halt or reduce production of melatonin. This is an important fact since it is blue light entering the eye and not, for example, bathing the skin

Blue light from the sun is important to cue for the wake portion of our sleep-wake cycle. However, the blue light from our digital devices may also be cueing us to stay awake during the night, when we should be getting ready for sleep21

Sleep is a very important factor in health. Lack of sleep can lead not only to short term effects like tiredness but also a myriad of chronic health problems such as heart disease, diabetes, high -blood pressure,  obesity, depression22, and even Alzheimer’s disease23

Therefore, it would be a good idea to reduce blue light exposure at night time to ensure we get good quality sleep, especially since we all live in an ecosystem where most people have to get up at the same time in the morning

Blue-light reduction built into smartphone operating systems and computer operating systems may be useful for late-night report writing. However, this has met mixed reviews24.

Lights around the home and your TV may not be able to reduce blue light emission, and this is where blue-blocking glasses could be useful.

Blue blocking glasses are generally in a form of am amber-like tint or a coating added to a lens

Studies have been performed and the results are mixed as well. Some studies say that there is promise25; conversely, some studies claim that there is no significant improvement26

There is no strict standard on blue-light blocking glasses in how much blue light is blocked or what particular wavelengths specifically as of writing. These tests would not have a particular standard, and this could be a possibility for the mixed results

The best remedy is most likely to limit screen use at night time and to reduce exposure to blue light. Additionally, look to change the light bulbs you have around the home to those with warmer colour temperatures. This would be the case of lights that you would use at night time before bed like the bedroom and lounge

Personally, I take sleep and health very seriously. I aim to not use a digital device an hour before bed. I opt for a relaxing chamomile tea and I would either read a book, draw a picture, write in my journal, or draft these blogs with pencil and paper

From this, we can establish that blue light may not cause any retinal health problems in the short term, but long term exposure at night time may affect sleep which has other health problems later down the track.


With a culture shifting towards a more health-conscious society, blue light’s harmful effects have come into question.

Due to the nature of light, blue light has more energy than other colours of the visible spectrum and therefore more potential for harm and damage.

However, blue light from digital devices is minuscule compared to the sun.

Exposure from digital devices may not harm the retina but it might harm our sleep if used at night time before bed, which has a cascade of long-term health problems such as heart problems and Alzheimer’s

Remedies for reduced blue light exposure might lie in blue-blocking glasses and applications that reduce blue light emission, but there is no robust study to prove this completely

The best thing seems to be limiting digital device use at night time for improved sleep and thus long term health.

If you enjoyed reading this and found it informative, comment on what you think and share this with others. Please subscribe to my newsletter to keep up-to-date and get in touch with me if you have any questions or want to discuss anything further.

  1. Facts & figures | Health Promotion Agency Smokefree[]
  2. Activity levels in New Zealand | Ministry of Health NZ[]
  3. Consensus Statement on Vitamin D and Sun Exposure in New Zealand[]
  4. Peak Sensitivity – an overview | Science Direct[]
  5. Additive Color: Theory & Definition[]
  6. Color Blindness Prevalence[]
  7. Wave-particle duality | physics | Britannica[]
  8. Photoelectric effect | physics | Britannica[]
  9. UV and ozone | NIWA[]
  10. Ultraviolet radiation and health | World Health Organisation[]
  11. Ultraviolet damage to the eye revisited – FB Cohen et al.[]
  12. Measurement of Emission Spectra of LED Light Bulbs : SHIMADZU[]
  13. Calculating the Emission Spectra from Common Light Sources[]
  14. Removal of the blue component of light significantly decreases retinal damage after high intensity exposure – ZC Zhao et al.[]
  15. Should You Be Worried About Blue Light? – American Academy of Ophthalmology[]
  16. Blink rate, incomplete blinks and computer vision syndrome –  JK Portello et al.[]
  17. Is Whole-Body Hydration an Important Consideration in Dry Eye? – Neil P. Walsh et al.[]
  18. Biological Rhythms: Types, Disorders, and Treatments[]
  19. The Effects of Red and Blue Lights on Circadian Variations in Cortisol, Alpha Amylase, and Melatonin – MG Figueiro et al.[]
  20. So Tired in the Morning… The Science of Sleep[]
  21. Blue light | Ministry of Health NZ[]
  22. Sleep Deprivation and Deficiency[]
  23. Sleep deprivation increases Alzheimer’s protein | National Institutes of Health[]
  24. Impacts of artificial blue light on health and the environment[]
  25. Blue blocking glasses worn at night in first year higher education students with sleep complaints: a feasibility study – GP Algorta et al.[]
  26. Blue-Light Filtering Spectacle Lenses: Optical and Clinical Performances – Tsz Wing Leung[]

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4 thoughts on “The Truth of Blue Light”

  1. Further research into this topic is definitely something I am looking forward to hearing about. As you have mentioned, current research lacks evidence to suggest that the blue light waves from our everyday use of digital devices are enough to cause significant damage to our retinal cells and I believe this was the RANZCO’s recent official view as well. I wonder whether the blue light waves are able to do any cumulative damage to our retinal cells with digital device use, especially with long-term(decades) use of these devices, in addition to the blue light waves we are exposed to from the sun. Also, it would be interesting to know whether blue light waves affect any other parts of the eyes, such as the cornea and the lens with long-term exposure and if so, by how much?
    We really need to know more about the role of blue light to be able to recommend the right management plans for our patients.

    1. Hi Ryan,

      Thank you for your comment. I think you have some very valid points. Things I am also wondering about too:
      1. Long term exposure to digital devices, cumulatively. But the idea is that sunlight is far more compared to digital device usage.
      2. Sunlight and blue light as we have protective measures against UV but nothing addressing blue light
      3. The effect on the cornea and lens would be interesting as well in terms of blue light as we know what UV light can do.
      4. I would like to see some standardisation of blue light in terms of what wavelength specifically to cut off and by how much.

      Please subscribe. to by newsletter for updates. I really appreciate your commenting and feedback.


  2. Hey Shivan,

    You mention the 20/20/20 rule; the middle 20 actually represents 20ft – since this is considered optical infinity – rather than 20m. In saying that, I’m totally guilty in telling my NZ patients that it stands for 20m for sake of simplicity!

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