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Blue light from smartphones. How and why is it reduced?

blue light from smartphone screen

Not so long ago, all the popular media, including respected tech sites, reported the following: “The new mobile OLED display from Samsung emits only 6.5% of blue light and has the most accurate color rendering!”.

There were many comments on this news, but not a single person asked how this was possible at all. How can a smartphone screen display saturated blue color without actually emitting blue light?

Obviously, it’s impossible! Either the screen emits all three primary colors, including the blue one, and has an accurate color rendering, or the screen doesn’t emit blue light and displays a blue sky in yellow.

Nevertheless, we hear similar statements at any flagship smartphone launch event. Manufacturers are proud of the fact that their new screens emit almost no harmful blue light and back up these claims with authoritative Eye Comfort certificates from TÜV Rheinland or SGS’s Eye Care Display:

tuv rheinland and sgs certificates

So what’s the catch or the point? How do modern screens have such a great color accuracy without emitting one of the three primary colors?

What does such a certificate really say, and should we look for a smartphone with such a display when it comes to eye health? What’s wrong with blue light, after all?

Once you read this article, you’ll understand why all displays emit far more blue light than is erroneously reported in the media. You’ll also learn what these certifications really mean and the benefits of certified displays.

Besides, this article will answer the question everyone has ever wondered – why all objects have different colors. Obviously, the apple is red because it absorbs all colors except red, which is reflected and reaches our eyes. But why does the apple “dislike” only red, and how exactly does it absorb other colors?

Let’s talk about all of this next!

Not all blue colors are alike! Or how do we really perceive colors?

There is a popular misconception that the human retina has three types of special photoreceptors called cones, which respond to red, green and blue light.

While there’s some truth to that, there are no red, green, or blue cones in reality. They are not colored in such colors, and, for instance, the “red cone” actively responds to green light and the “green cone” to red and blue.

The image in our consciousness is created a bit differently, and therein lies the “secret” of modern displays, which “remove the blue light” while still giving us the feeling of blue.

Just a few words about the color itself

As you know, color is only a figment of our imagination. There are only electromagnetic waves permeating space, in reality. Each wave has a length – the distance between its crests:

what is wavelength

If this distance is about 5 inches, we call it Wi-Fi or Bluetooth. If the wavelength is 118 inches, we call it FM radio. We certainly can’t see either of these waves. But if a wave with 600 nanometers (0.000024″) between its crests enters our eyes, we feel red color.

In other words, we can only see electromagnetic waves of a certain length – from 400 to 700 nanometers. And each color corresponds to an electromagnetic wave of a particular length:

visible light spectrum

If that makes sense, then we go back to the cones.

Three sizes to fit all!

We have three types of cones indeed, and each of them contains discs with opsins – special molecules that can absorb light:

cone with photopigments

A cone’s response to a certain color depends solely on a molecule type (photopigment) located in its discs.

If we take a look at the graph of light absorption by erythrolabe molecule (more commonly known as the “red cone”), we will see this:

l cone sensitivity

It shows the probability of light absorption depending on the wavelength. Here we see that the “red cone” will perfectly absorb red color (from 630 nm and higher) as well as yellow, green, and even will respond to blue light!

Therefore, instead of red, it’s more correct to call it L cone (L for long) because it responds the most to long wavelengths.

On the other hand, the “blue cones” will also respond a little to green colors, but its peak sensitivity will be at short (S) waves. Hence the name S cones:

s cone sensitivity

M cones are most sensitive to green light ~550 nm (medium-wavelength) but absorb a lot of other colors as well:

m cone sensitivity

It’s important to understand that we can induce the sensation of the same color by stimulating cones with the light of different wavelengths.

Let’s take a simple example. Imagine that a beam of blue light, consisting of different wavelengths between 370 and 480 nanometers, enters our eyes:

blue light spectrum sample 1

All these waves will “merge” together and give us the feeling of a certain shade of blue. But we would see precisely the same shade of blue if a completely different set of waves hit our eyes:

blue light spectrum sample 2

As you can see, now there is almost no light up to 420 nm, although there was a lot of it before. But, at the same time, there is more light at 450 nm than previously.

So why do we perceive such a different set of light waves as the same shade of blue?

The answer is actually quite simple.

Our brain doesn’t count each wavelength. It receives just a single “value” – a total signal level from each of the three types of cones. It makes no difference how much S cones were stimulated by 380 nm or 450 nm light. The main thing is the total signal from cones in some area of the retina.

We saw just above that the S cones have very low sensitivity in the range up to 400 nm, and the sensitivity peak around 450 nm. So we can either illuminate the S cones with all “shades of blue” from 380 to 500 nm of medium intensity or remove all waves up to 420 nm and increase the intensity of the 450 nm waves.

As a result, the total level of the signal from the S cones will be the same in both cases. We simply composed it from many small signals in the first case and from a single powerful signal in the second case.

The same is true for any other color. It doesn’t matter which electromagnetic waves (colors) it consists of. If the total signal from S, M, and L cones is the same, we’ll see the same color. Even though two light beams had completely different spectrums (electromagnetic waves of different lengths in different proportions).

Here is a good example of the same yellow consisting of a completely different spectrums:

different wavelengths, same color

The light from the ball on the left consists only of a single wavelength which stimulates both M and L cones. But the light on the right doesn’t include this wavelength at all and still induces the same color feeling. It’s because the total signal from all three types of cones in these cases is the same:

cones response level

This property of our vision is called metamerism. And this is what the harmful blue light reduction is based on.

Harmful and useful blue light. Or what exactly are the manufacturers reducing?

In 2019, Samsung actually released AMOLED displays that emit only 7.5% of harmful blue light. A year later, the company introduced a new generation of displays that reduced this figure to 6.5%.

Today, science considers blue light only with a wavelength up to 455 nanometers potentially dangerous. Anything above is considered safe for health:

visible light spectrum

When it comes to blue light reduction, all manufacturers imply a percentage of light emitted from 415 to 455 nm, while the wavelength of blue light can be as high as 500 nm. Therefore, if Samsung claims that a smartphone has an Eye Care Display certification from SGS, it means the amount of light it emits between 415 and 455 nm is only 6.5% of the total amount of light emitted.

Other standards (e.g., Eyesafe) require the amount of blue light in the 415 to 455 nm range to be less than 50% of the total blue light (400 to 500 nm).

Interestingly, IPS displays have a higher level of radiation in the “harmful range” than AMOLED screens in general. This is because they use blue LEDs as the backlight, which have a radiation peak of around 450 nm:

white led

The phosphor inside the LED absorbs some of this blue light and re-emits it in yellow color due to the Stokes shift. The rest of the blue light emits outward, and the resulting mixing of blue and yellow light makes the bulb appear white.

Removing the blue light and improving color accuracy

So, manufacturers need to somehow change the light spectrum by removing part of it without affecting the color accuracy.

If they simply reduce the amount of light within a range up to 455 nm (“harmful blue light”), the screen will have a noticeable yellow tint, and it will be very uncomfortable to use such a display:

bad blue light filter

But there is another solution. As we’ve already discussed, if the total signal from cones is identical, our eyes will see the same color no matter which wavelength it’s composed of.

Accordingly, if we reduce the amount of light in the range up to 455 nanometers (for example, by using other materials for the blue LED), we need to increase the amount of light in the range from 455 to 475 nanometers:

good blue light filter

In this case, the light will have a slightly different “composition”, but the total signal from the retinal S cones will be the same. Therefore, the new light spectrum will not affect color accuracy in any way.

Both screens should display an identical color, and we will not be able to distinguish which of them consists of more “harmful” blue light. So both “wavelengths set” will cause us to feel the same color.

Thus, an SGS or TÜV Rheinland certificate guarantees that the light from a particular smartphone does not contain (or contains negligible amounts of) wavelengths up to 455 nanometers.

That’s the whole secret of the trendy “blue light” reduction. And actually, we are done here! But if you want to know more, I suggest you keep reading.

What’s wrong with blue light in the range up to 455 nm? The whole truth about HEV radiation

Any electromagnetic radiation, be it FM radio, 5G, or visible light, is a flow of pure energy. Accordingly, this energy can be transferred to matter, and what will happen to this matter depends on the amount and type of energy.

We considered light as a wave in this article. But light, just like any other electromagnetic radiation, is also a flow of particles called photons. For the sake of simplicity, you can imagine photons as tiny indivisible waves:

photons as a wave

Now the “photon wavelength” makes some sense, and we can imagine photons of different colors. For instance, a “red photon” will have a long wave, and a “blue photon” will have a short wave:

photon and wavelength

There is only one difference between radio waves, heat (infrared), 5G, visible light, ultraviolet, or X-rays. That is the wavelength of the photon or wavelength of light, which is essentially the same thing.

So why are short wavelengths more dangerous than long ones? For example, why can ultraviolet radiation (100 to 400 nm) cause skin cancer and other problems while red light (620-740 nanometers) is completely harmless in most cases?

The fact is that the shorter the wavelength, the more oscillations of the electromagnetic field occur in a point of space per unit time. For instance, if we want an electromagnetic field to oscillate 450 trillion times per second, a photon must have enormous energy. And this energy corresponds to a wavelength of 400 nanometers (0.000016 inches) or ultraviolet radiation.

The 5G wavelength for comparison does not exceed 2 inches (if we don’t consider the millimeter range). The photons have much less energy in this case because 5G waves oscillate 75,000 times slower than ultraviolet radiation in the “safest” near field (UVA).

The same goes for all colors. Blue light borders on ultraviolet light at 400 nm. And the longer the wave becomes, the less energy its photons have. Accordingly, today science identifies the so-called HEV-radiation or high-energy visible light which includes blue color.

The direct threat is not proven, but…

Over the past 50 years, the number of studies on the danger of blue light has grown exponentially.

Here are just a tiny fraction of these studies, published in the most reputable publications like PubMed, Scientific Reports, or Nature (DOI references for citing scientific papers):

One way or another, they all talk about the potential of blue light to cause various photochemical damages both to photoreceptors and the retina itself. More precisely, its pigment epithelium, which performs a huge number of important functions related to vision.

But the problem with these studies is that they prove only indirect harm. They are conducted either on animals instead of humans or on individual human cells, which have lost various repair and protection mechanisms after extraction from the body. Or unreal conditions are created in general, such as continuous prolonged irradiation with very powerful blue light.

Therefore, science today does not claim that blue light is a proven cause of vision problems.

Moreover, gadgets are not the primary source of HEV radiation at all. Because the main source is the sun. Approximately 25-30% of sunlight composition is the same electromagnetic waves in the HEV range up to 500 nm:

sunlight spectrum vs blue light

Anyway, science is concerned that modern people spend too much time in front of screens. This is especially true for children because the older a person is, the more the lens absorbs UV and blue light up to 460 nm. This means that less of this light will reach the retina.

To fully understand the essence of the problem, only the last question remains to be answered. The most difficult one to understand.

How can light destroy molecules and DNA? Or why is an apple red?

We’ve talked a lot about the potential harm of blue light since “blue” photons contain more energy than green and, even more so, red ones. But how exactly does this energy “dissolve” in cells or molecules of any substance?

We all have a rough idea of what an atom looks like. It’s a tiny positively charged nucleus consisting of protons and neutrons, surrounded by a negatively charged electron cloud:

atomic cloud

Because of the negatively charged electrons, many atoms can bond together into molecules. For example, two atoms can share a single electron and thus “stick together”.

Electrons around the atom can be at different energy levels, i.e., they can “fly” in different orbitals. And to move from one energy level to another (or from one orbital to another), the electron must receive a certain amount of energy.

In simple words, the energy level is the amount of energy that an electron needs to have to be in a particular orbital. If the electron is on the last energy level, i.e., it has the most energy, it can fly away from the atom and go “free floating”.

To remind you, a photon is a pure energy. Moreover, each photon has its own specific and indivisible portion of energy. Red light photons (625 nm) contain 1.68 eV of energy, “green” photons (500 nm) – 2.19 eV of energy, and blue ones (440 nm) – 2.56 eV. The shorter the wavelength, the more energy a photon has.

Accordingly, when a photon hits an electron, it can fully transfer its energy and disappear. Then the electron, having increased its energy, “jumps” to a new energy level of the atom, i.e., changes its orbital.

The higher the photon’s energy, the higher electron can “jumps”. Again, the electron can completely leave the atom at a certain energy.

If that’s clear, then let’s move on.

Molecular orbitals

When multiple atoms combine chemically into a molecule, their electron clouds also combine to form molecular orbitals:

two atoms with their electron clouds

And now, we are dealing with whole molecule energy levels instead of individual atoms’ energy levels. So the atomic model can be applied to the entire molecule.

Accordingly, now photon hits a molecule (e.g. DNA), and if it has enough energy, that energy is transferred to a certain electron, and it jumps to a new molecular orbital.

There is an important detail worth clarifying here. Molecules have three types of orbitals:

  • Bonding
  • Antibonding
  • Nonbonding

We are only interested in the first two. The more electrons are floating on the bonding orbital, the stronger the bond of the atoms of this molecule. But if the electrons start jumping to the antibonding orbitals, the bond weakens.

Therefore, the worst-case scenario for a molecule is photons with high enough energy to force electrons to jump from bonding orbitals to antibonding ones.

Take DNA as an example. When high-energy photons hit this molecule, they give their energy to certain electrons. And these electrons jump to antibonding orbitals, which cause some bonds in the molecule to break.

The broken parts are very unstable since other positively charged particles attract them. Because of this, neighboring nucleotides can stick together to form pyrimidine dimers:

DNA damage by uv light

As a result, local DNA structure disruptions cause mutations since it’s very difficult to read the instruction and work with such DNA. This can lead to cancer. The scenario described in particular is the mechanism behind melanoma formation when exposed to solar ultraviolet radiation.

As you can see, photons can be very dangerous. But, again, the level of danger is directly related to the amount of photon energy, which, in turn, directly depends on the electromagnetic wavelength.

So why is the apple red?

The color of any material depends solely on the structure of the molecules it’s composed of. Each particular molecule has its own energy levels. In a molecule, energy levels can be far apart, and an electron needs a large portion of external energy to jump to another level:

energy levels and electron jumps

Accordingly, when a low-energy photon flies nearby (for example, a red photon), the electron doesn’t care about it, because the energy of this photon is not enough to “jump”. So it doesn’t absorb this photon.

An electron simply can’t take energy partially. It either completely absorbs the whole photon with all its energy and immediately makes a jump or ignores it if the photon energy is not enough to move to a higher energy level.

Such a substance can be orange because its electrons ignore the red and green “photons” with insufficient energy but actively absorb the blue ones, which causes electrons to move around the molecule’s orbitals.

As a result, red and green light waves are reflected from the substance. And we see a mixture of these, an orange color.

Again, the color of the substance (which photons it will absorb) depends on the molecular orbitals, on how much energy it takes for the electrons of a particular molecule to jump to a higher energy level.

Of course, the substance will not be destroyed. Because the electrons, being in such a “stressed” state, will want to return to their former orbitals. And they will do it instantly, throwing off excess energy in the form of insignificant heat.

Almost the same happens with our vision. When light hits a cone, it changes the structure of the photopigment molecule. This change triggers the whole cascade of reactions, leading to the appearance of an electrical signal transmitted to the brain.

Then the molecule recovers and is ready for a new dose of visible light irradiation. But some of the photons always miss the cones and rods, reaching the pigment epithelium of the retina. And this epithelium absorbs the whole visible spectrum.

This is why blue light raises questions, especially in the range close to ultraviolet radiation. Too much energy is contained in its photons.

Alex Salo, Tech Longreads founder

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