Does Turning on the Front Light on a Color E Ink Screen Negate Its Eye-Friendly Purpose?
Before we begin, I recommend clicking the "eink" button in the top right corner for a better reading experience! (In this mode, if you want to open a hyperlink or enlarge an image, please long-press and select "open link". If you are using a computer, you can right-click and select "Open link in a new tab." You can also navigate this mode by left/right arrows on keyboard.)
(This article is an English translation of my original work, written on May 20, 2022. Here is the original script)
Someone in a Facebook group recently raised the question: "Isn't the purpose of using E Ink to achieve eye-strain-free reading through its non-emissive nature, relying solely on reflected ambient light? However, the color version requires the front light [Note 1] to be activated for clear visibility. Doesn't this conflict with the original product's focus?"
Additionally, some people also feel that E Ink with the front light turned on is uncomfortable. Even if the intensity is very low, their eyes just cannot tolerate that little bit more light, not even a tiny bit.
Actually, people who have the above thoughts mistakenly believe that the reason why E Ink is more eye-friendly is that E Ink is not self-illuminating. They think that general mobile phones and tablets have a light-emitting backlight that continuously emits light directly into the eyes, which hurts the eyes and makes them uncomfortable. But actually, this is completely a wrong idea. Below, I will explain the reasons.
Table of Content
- Direct Light Is No Different From Reflected Light
- Front Light Is Essentially the Same as Ambient Light
- Reasons Why Backlights of Phones and Tablets Are Harmful to the Eyes
- Reasons Why E Ink is Eye-Friendly.
- Does Turning on the Front Light Really Hurt the Eyes?
- Why Do I Rarely Turn on the Front Light?
- Questions Worth Considering and Researching
- Conclusion
- Appendix
- Note
Direct Light Is No Different From Reflected Light
Our eyes are naturally designed to receive light signals. From the moment we open our eyes after birth, our eyes are constantly receiving light stimulation. We need light to see things. Now comes the contradictory point: If there's no light come from the surface of E Ink device, how can we see it? Some people say it's reflected light, not self-emitted light, but what's the difference between the reflected light and the light emitted by a light source? In fact, there is absolutely no difference between the two [Note 2]. Therefore, the surface of E Ink undoubtedly emits light continuously, originating from the reflection of ambient light sources.
Let me ask again: Isn't reflected light directly shining into our eyes? If it's not directly shining into our eyes, wouldn't the E Ink screen we see be a mirage? When you reach out to touch the screen, you should be able to accurately press the buttons, right? Since you can, we can confirm that reflected light does directly shine into our eyes.
Since we've established that E Ink continuously emits light directly into our eyes, how does this differ from the continuous backlight of phones and tablets that also shines directly into our eyes? If there is no difference, why do we clearly feel that our eyes are much more comfortable when we read on E Ink for a long time compared to looking at backlit tablets or mobile phones? We will answer this question later.
Front Light Is Essentially the Same as Ambient Light
Now, let's shift our focus to the front light of E Ink. The so-called front light of E Ink consists of LED beads installed on the side and top of the E Ink screen. The light it emits passes through a light guide plate to be evenly distributed to the middle of the screen and illuminates the ink particles. The ink particles then reflect this light back to us so we can see it. Therefore, it is also reflected light. So, what is the difference between this reflected light and the light from an LED light on the ceiling, an LED light on a desk lamp, or sunlight that shines on E Ink and is then reflected back? Isn't the light from indoor lamps or desk lamps considered ambient light? Then, when you turn on the light on an E Ink screen, wouldn't that also be ambient light? Does calling it a front light somehow change its nature? Can you truly tell them apart? If you think you can, please look at the following two pictures:
These photos show a color E Ink Boox Nova 3 Color with and without the front light turned on. Could you tell me which photo shows the front light on?
Have you chosen your answer?
Click to see the Answer
From the above demonstration, you can see that the front light and ambient light are actually not fundamentally different. If you are not given the brightness level of the background environment as a reference, you basically have no way of knowing whether the front light is turned on for reflective screen.
 |
| From the above picture, we can see that both the front light and ambient light rely on reflection to transmit colored light to our eyes, the only difference being that one is closer to the screen and the other is further away. |
Some people say that when the front light is turned on, their eyes cannot tolerate that extra little bit of light. As demonstrated above, the absolute brightness of a screen with the front light on isn't always greater than one without it under good lighting; in fact, it can sometimes be darker. Does it then make sense that someone would say they can't tolerate that tiny bit of extra front light?
What's particularly interesting is that color E Ink screens tend to be darker because the color filter absorbs some ambient light. So, logically, shouldn't we add a little more light to compensate for what's absorbed? If the front light is adjusted just right to make up for the light lost by the filter, why would using it be considered harmful to the eyes?
After such an explanation, does it make sense now?
Reasons Why Backlights of Phones and Tablets Are Harmful to the Eyes
We can now elaborate on why mobile phones and tablets are more prone to causing eye discomfort like stinging and soreness. These direct-light emitting displays require their backlights to be more intense than the ambient light to ensure good color brightness and contrast. When ambient light surpasses the backlight's intensity, color and contrast diminish, the screen darkens, and reflections from the ambient light can even completely obscure the display, rendering it illegible.
This is what happens when you look at a mobile phone under strong sunlight. That's why newer mobile phones increasingly pursue maximum peak screen brightness. For example, the iPhone 13 reaches a maximum peak brightness of 1200 nits, precisely to ensure relatively viewable display quality even outdoors.
 |
| backlit phones have extremely poor display quality under strong light. |
Consequently, the brightness of mobile phone and tablet screens remains independent (stronger) of the ambient light in your surroundings. You might not even notice subtle shifts in shadows on the screen, and it's impossible to discern the actual color temperature of your environment. So, what issues arise from this disconnect between screen brightness and ambient light?
Human eyes actually regulate the amount of light entering by controlling the size of the pupils, similar to the aperture of a single-lens reflex camera. Why is controlling the amount of incoming light necessary? Because the photoreceptor cells in the retina have a limited capacity to handle energy; exceeding this limit can cause damage. Therefore, the human body's design is incredibly intricate and intelligent. When people accidentally encounter strong light, they instinctively blink or close their eyes, also to protect them from damage. So, how do our eyes decide how much to open the pupils? This decision is based on the current ambient light.
 |
| The brightness of backlight screens is disconnected from the environment, and they can even act as flashlights in the dark. |
So, has everyone noticed where the problem lies? The eyes regulate pupil size based on the ambient light sources, not based on the brightness of mobile phones or tablets, because the screens of mobile phones and tablets only occupy a small portion of the eye's field of vision [Note 3]. However, the screens of mobile phones and tablets are much brighter than the ambient light. Therefore, the eye's protective mechanism for adjustment is basically ineffective in this area, because the area receiving this image will constantly absorb stronger light. In terms of a photograph, it's like having an area that is constantly overexposed, continuously absorbing more energy. Do you think this won't cause problems in the long run?
 |
| Take a close look, the illumination range of a desk lamp is very large, allowing the eye's pupils to adjust to the light around the E Ink. |
Reasons Why E Ink is Eye-Friendly.
E Ink without the front light behaves just like ordinary paper, seamlessly integrating with the ambient light and adapting to its changes. From morning to evening, the screen's colors and brightness will naturally shift, allowing our eyes to continuously adjust pupil size according to the environment. Because the light reflected by E Ink mirrors the surrounding light, there are no intensely bright spots to overwhelm the photoreceptor cells, making it significantly more comfortable for extended reading.
Now we talk about color E Ink. Because color E Ink has a layer of color filter on its surface, just like wearing sunglasses, it will absorb a portion of the ambient light. Therefore, the screen area of color E Ink will actually be darker than the surrounding environment. But this indicates that the cells receiving this image bear even less energy. Therefore, as long as the screen contrast is sufficient to discern text, color E Ink is even more eye-friendly.
Many people tend to compare the screen brightness of color E Ink to that of regular paper or black and white E Ink. While humans naturally compare things, finding the color E Ink less bright, especially given the cost, can lead to dissatisfaction. However, does this absolute brightness of color E Ink make it unsuitable for reading? Not really. Having used color E Ink for over a year, alongside black and white, I haven't found the color version less comfortable for reading; in fact, I find the colors enhance my enjoyment.
Does Turning on the Front Light Really Hurt the Eyes?
However, there will be exceptions in any case. If the front light brightness on a color E Ink device isn't adjusted properly and exceeds the amount absorbed by the filter, it could become as harmful as a light-emitting mobile phone or tablet in that the screen area is brighter than the ambient light. Some people might turn the front light to the brightest setting to make the colors on a color E Ink device appear more vibrant (you could say it's like adding extra seasoning for a stronger flavor!), but this would be just as harmful to the eyes as using a mobile phone or tablet! Therefore, those who say that using the front light on a color E Ink device is uncomfortable are probably adjusting the front light intensity improperly.
Another situation that is equally harmful to the eyes is using the front light in a completely dark environment, such as lying in bed at night with the room lights off and relying solely on the E Ink device's front light for reading. This is definitely harmful! This is because, with current e-readers, even the lowest setting of the front light creates a brightness that is inherently detached from a completely dark environment. True darkness should imply the inability to see anything at all, so the fact that the screen remains visible indicates a disconnect.
It's true that some may need to use their devices in low-light conditions, like dimmed meeting rooms or dark buses, for tasks such as note-taking or reading. They might wonder how to do so without the front light. However, we should recall how we would have managed with paper books or notebooks in similar environments before the digital age. Opting for the front light in these instances might come at the expense of some eye health. Our reliance on smartphones and tablets has cultivated a habit of expecting constant screen visibility, which is often an unnatural condition. For the sake of our eyes, it's wise to break these habits.
Why Do I Rarely Turn on the Front Light?
Those familiar with my writing will know that I use the front light on my color E Ink very infrequently – for over 95% of my reading, it's off. This doesn't mean I'm against it, and I do use it when required. Here are my main reasons for not using it often or generally preferring not to:
- My usual reading environment has plenty of natural light during the day, and at night, I always sit at my desk and use a desk lamp to read, so insufficient lighting is not an issue.
- With the front light on, due to a more noticeable light scattering effect, the screen's color saturation and contrast are lower than when the front light is off [Note 4]. Moreover, a poorly designed front light can also cause color casts. I have experimentally proven this in my previous articles "The Front Light Myth of Color E Ink" and "How to Use the Front Light of Boox Nova Air C to Make Colors More Beautiful?", which interested readers can refer to.
- Turning on the front light consumes a bit more power, reducing battery life.
- Most e-readers currently lack the function to automatically adjust the front light to a suitable level based on ambient light, although Hisense phones have this feature, it's still not ideal [Note 5]. If I turn on the front light, I have to constantly pay attention and adjust it whenever the surrounding ambient light changes to ensure that the screen area is not brighter than the ambient light. However, when I'm focused, I often forget this, or having to adjust it all the time is very troublesome. In that case, I might as well just slightly turn the device or adjust my position to let the screen catch more ambient light, which is more convenient and saves trouble.
Questions Worth Considering and Researching
Using E Ink to write articles has one drawback: because your eyes don't get tired, you can inadvertently write very lengthy pieces. Having discussed so much above, I hope everyone has gained something from it. However, I believe the most important question for everyone to carefully consider is: What level of brightness is actually sufficient for reading? Why do most people consider paper the gold standard? Why do some consider black and white E Ink the gold standard? The Illuminating Engineering Society recommends 300-500 Lux. What is the basis for the values they set? Is there medical research proving that this is the optimal illuminance? Furthermore, there are different types of paper, and black and white E Ink also has different shades of white. What's more, the surface brightness of these things is constantly changing under different lighting conditions. So, what is your personal gold standard? I hope everyone will seriously ponder the answer to this question.
Conclusion
A color E Ink device's front light works similarly to artificial ambient light sources like a desk lamp, reflecting light off the ink particles to your eyes, in contrast to the direct light emission of backlit LCD, OLED, Mini LED, or Micro LED screens. If the front light is used correctly to integrate with the ambient light, it provides a comfortable and eye-friendly reading experience. However, when used improperly, creating a noticeable difference in brightness compared to the surroundings, it can be as damaging to your eyes as a backlit display. Consequently, whether the front light preserves the eye-friendly nature of E Ink, given the current lack of sophisticated automatic brightness controls, rests on the user's understanding and correct application.
Appendix
Paper Similarity Index, PSI
The comfort of reading on a screen depends on other factors besides whether the screen brightness mentioned in this article integrates with ambient light (environmental adaptation characteristics). TÜV Rheinland has defined the Paper-like Index (PSI) for reflective displays. The higher the score of this index, the closer it is to the reading experience and comfort of paper. Those interested in learning about other factors can refer to a recently released video by TÜV Rheinland:
Note
Note 1: The original text mentioned backlight, but E Ink does not use a backlight source like LCD or LED screens to directly emit light to form an image. Instead, it uses a front light source positioned in front of the screen to illuminate the ink particles, which then reflect the colored light of the ink to the eyes.⤴️
Note 2: If you really have to point out a difference, when direct light hits an object's surface and is reflected, the reflected light's phase and polarization will change.⤴️
Note 3: f you want it to occupy most of your field of vision, you need to hold it very close. Besides being unable to focus properly, reading at such a close distance for a long time is more likely to cause nearsightedness. Furthermore, the closer the distance, the more intense the energy (inversely proportional to the square of the distance), making it easier to absorb stronger light.⤴️
Note 4: However, the latest generation of Kaleido Plus 2 has improved the front light to the point where the displayed color saturation and contrast are close to the effect when the front light is off.⤴️
Note 5: Hisense does a great job because its front light brightness is also adjusted specifically for the characteristics of E Ink, compensating for the portion absorbed by the color filter. However, because its adjustment has only 36 levels and lacks continuous fine-tuning, it is sometimes difficult to accurately match the ambient light. My current impression is that the Auto mode still tends to be a bit too bright, and its adjustment speed is slow when the ambient light changes suddenly.⤴️
About the Author
Jack Black
|
Driven by a passion for physics, science, and engineering, I seek to leverage my medical experience to advance human health and environmental sustainability. |
|
If you liked what I wrote, feel free to support me. It'll give me more motivation to create. Thanks! |
|
發表文章
留言
張貼留言