Nowadays, smartphones equipped with OLED screens are sprouting up like bamboo shoots after a rain

With its popularity

There is a saying that is also rampant

OLED is harmful to the eyes

I will never be a slave to LCD

So does OLED harm the eyes?

Let’s investigate below

First, we need to understand what OLED is

And its working mechanism

OLED, Organic Light-Emitting Diode

The biggest feature is self-luminous

It is also the biggest difference from traditional LCD screens

(It is wrong to call it an LED screen,

LED is just its backlight technology)

Speaking of which, OLED also has classifications

Samsung uses RGB OLED

That is, each pixel has three diodes

Each diode has red, green, and blue three primary colors

They can form different colors independently

LG uses WRGB OLED

Unlike the former

The diode emits white light

And then restores the three primary colors through RGBW four-color filter

Then different colors are formed through combination

Next is the key point

Each pixel in OLED can self-illuminate

By controlling the brightness of the light-emitting material to form different colors

So how to control it?

We know that power = current × voltage

Under certain circumstances

OLED screens achieve brightness changes by controlling the current

That is the so-called DC dimming

As shown in the figure, the relationship between voltage and current density and the relationship between voltage and brightness

They are basically a power function

This is too precise for tuning

It is destined to be unbearable for screen manufacturers

Using current to drive brightness is much more convenient

Basically, it is a straight line

But then the problem arises

Under DC dimming

Low-brightness OLED screens have very uneven color distribution

(Different wavelengths of the three primary colors

Color deviation occurs at low brightness)

If you want to correct the screen color

The cost and technical difficulty are too great

When soldiers come, generals block, and water comes, earth covers

However

What can stump great humans?

Since DC and OLED don’t match

Then change to a different solution

Thus, our protagonist

Finally emerged

To save OLED from danger

The man

Is calledPWM

Once PWM was launched

It solved the problem of color deviation at low brightness

How was it achieved?

It’s quite simple, similar to alternating current

In fact, it is achieved by constantly turning the screen on and off to adjust brightness

Human eyes have a visual persistence

As long as the speed is fast enough

And the time the screen is lit in one second is long enough

The interval between each time the screen is lit is short enough

People will judge that the screen is bright enough

If you need to reduce brightness

Just increase the interval time for each time the screen is lit

You will feel that the screen is getting darker

This approach seems clever

But it has also been criticized by the LCD camp

OLED uses PWM dimming at low brightness

Its frequency is usually only 240HZ

This belongs to the low-frequency category

Also known as

Low-frequency PWM dazzling

Is it really like that?

The main controversy comes from CQC1601-2016

“Visual Work Table Lamp Certification Technical Specification”

Its requirement

Flicker should comply with IEEE Std 1789-2015 standards

(IEEE, Institute of Electrical and Electronics Engineers)

The green area in the figure indicates no harm

And the yellow area is low risk

The white area is high risk

Under this standard

The flicker frequency with low health risk should be above 1250Hz

In the LCD camp, low-frequency OLED screens are simply

A devil-like existence

There are also related testing agencies in China

Testing against this standard

If the light output frequency is greater than 3125HZ

It will be exempt from assessment, considered flicker-free

But

All thesestandards are about lamps

About lighting lamps

Not applicable to displays

And this report itself also has problems

First, it follows the old MD standard

Without considering other complex factors

Secondly, its indicators are too strict

IEEE also revised the document in 2017

Therefore, we can roughly assume

Netizens took an outdated standard

To judge mobile phone displays

And it is stilla standard for lighting fixtures

In fact, there are not only this standard

For example, the International Lighting Commission CIE’s

TN006-2016

The International Electrotechnical Commission IEC’s

TR64547-1

Have introduced other complex variables

At the same time, at the latest CIE conference

The CIE 2006 evaluation model was widely recognized

Of course, it is not to say that PWM dimming has no effect on the eyes

Low-frequency flicker willcause eye fatigue

After using the screen for a long time

It often makes people feel uncomfortable in their eyes

But regarding low-frequency eye harm

There is currently noconclusive evidence

However, everyone is praising LCD

Is LCD really that eye-friendly?

Not really

LCD can indeed reduce brightness through DC dimming

By controlling the current of the backlight component

However, not all LCD phones

Will choose DC dimming

There are still many phones that will choose PWM dimming

But in general

The frequency is much higher than that of OLED

Concentrated around 2kHZ

But there are still a few models that also use low-frequency PWM

Speaking of which, let’s talk about the issue of short-wave blue light in mobile phones

As mentioned earlier, LED requires a white backlight layer

So how is white produced?

It is usually created by using yellow phosphor

Mixed with blue LED lights

Thus, short-wave blue light is inevitably generated

(Wavelength less than 450mm)

This blue light has strong energy

And great penetration

Not friendly to the eyes

Whether it causes damage is still inconclusive

But blue light is not good for people’s routines

It affects sleep quality

Currently, mobile phones have eye protection modes

It is recommended toturn it on for use

It can effectively filter out some blue light

Effectively reduce visual fatigue

However, the blue light in OLED screens is significantly reduced compared to LCD

Data shows this value is78%

Finally, let me teach you how to identify

Whether the mobile phone has flicker

Open the camera of another mobile phone

Lower the brightness of your own phone

Generally, you will seestripes on the screen

OLED has flicker

LCD has blue light

For consumers

Both types of screens have drawbacks

In fact, to protect the eyes

It still needs to start from oneself

Play less on the phone and sleep more

Resting the eyes is the most important

If you can’t control it

Don’t let the screen take the blame for you