Putting this kind of film on your phone will really ruin your eyes... Urgent reminder →

A user posted that after using a privacy film in May 2023, the degree of myopia in his eyes, which was not originally myopic, reached 300 degrees in just two months, and reached 475 degrees after a year.

Image source: Internet

On Quora, a user reported that after using the privacy film for two or three months, he began to feel "going blind", there seemed to be always dark shadows in front of his eyes, and his cornea was often congested and red.

Image source: quora

Some users on Reddit also reported that they experienced symptoms such as headaches, eyestrain, and dizziness after using privacy filters, and some even required medication to relieve the symptoms, which lasted for up to several months.

Image source: Internet

What is going on? Does privacy film really damage eyesight?

Privacy film. Source: Internet

In 1904, British inventor Harold Dennis Taylor used chemical methods to coat glass with a thin film that successfully weakened light reflections, like a veil over a lens. In 1935, Ukrainian physicist Oleksandr Smakula further improved the technology and invented an anti-reflective coating based on the principle of interference.

Oleksandr SmakulaPhoto source: euromaidanpress

By the late 1990s, as portable electronic devices became more and more popular, privacy issues became more pressing. Scientists and engineers began to wonder: Is there a way to make the screen content visible only to the user facing the front, while being blurred from the side?

Image source: aliexpress

The answer lies in micro-louver technology. Just like the louvers at home, which control light by adjusting the angle, engineers embed tiny vertical louver structures in the film to allow light to propagate only in a specific direction. When viewed from the front, the screen is clear as usual; when viewed from the side, it is blurry or even completely black.

Image source: Document 4

Its development was not smooth sailing. The initial version was crude and simple, mainly used on business laptops and bank ATMs to protect sensitive information from being peeped. After repeated trials and optimizations, the privacy film gradually became thinner and more durable, and its application range was also expanded to smartphones and tablets, becoming a "privacy artifact" that ordinary people can also use.

When the user views the screen from the front (close to 0° viewing angle), light can pass through normally and the screen content is clearly visible; when viewed from the side, the blinds block the light, making the screen appear blurry or dark. This technology was first developed by 3M and is widely used in modern privacy film products.

Image source: aliexpress

Although micro-blind technology performs well in privacy protection, its changes to screen display performance may affect the user's eyesight.

According to a 2024 study of privacy film performance, privacy films can reduce screen brightness by 24.8% to 53.8% when viewed head-on, depending on product design and quality. This change forces users to turn up screen brightness to maintain clarity.

However, turning up the brightness increases exposure to blue light. Blue light (wavelength of about 400-500 nanometers) is a high-energy, short-wave light. Studies have shown that long-term exposure to blue light may cause eye fatigue, dry eyes, and interfere with sleep quality. In addition, low-brightness and low-contrast screens may cause pupils to continue to dilate to capture more light, increasing the burden on eye adjustment and inducing visual fatigue.

Image source: atuloptikos

Moreover, blue light is not only associated with eye fatigue, but may also cause potential damage to the retina. According to a 2018 study, blue light can penetrate the cornea and lens and directly reach the retina, causing photochemical damage. Experiments have shown that blue light exposure increases calcium ion levels in retinal pigment epithelial cells, leading to local cell apoptosis.

In 2023, a study based on epidemiological and clinical observations found that long-term exposure to high-intensity blue light (such as occupational LED lights) is associated with an increased incidence of age-related macular degeneration. Retinal pigment epithelial cells are susceptible to photochemical damage due to the accumulation of light-absorbing molecules (such as lipofuscin).

Although there is currently no sufficient evidence to prove that blue light exposure from privacy films will cause irreversible vision loss, long-term and high-intensity use may aggravate eye discomfort.

The screen went dark, the text edges looked foggy, and the colors were not right—icons became dim, and blue links turned gray. Image source: Internet

In addition, privacy films have another characteristic, which can cause screen color distortion, especially in low-quality products. Studies have shown that color distortion and reduced contrast can reduce visual acuity, especially in low-light or low-contrast conditions.

TV under privacy film Source: Internet

For example, light gray text on a white background (common on web pages) has low contrast. After the privacy film reduces the brightness, the edges of the text are blurred, making reading more difficult. Experiments show that under such conditions, the time it takes for subjects to recognize characters increases by about 30%, and the error rate increases by 20%. In the previous case, someone mentioned the phenomenon of "dark shadows in front of the eyes". The reason for this may be that the brain needs to process distorted visual information, thereby increasing the burden on the eyes and nervous system.

If you must use a privacy film, it is recommended to use a high-quality product, such as a PET-based privacy film. This type of privacy film usually maintains a high light transmittance and clarity, which can reduce the burden on the eyes.

Surfshark, a company known for its online privacy and security, conducted an in-depth discussion on the performance and effectiveness of privacy screen protectors in its article "What Are Privacy Screen Protectors and Are They Effective?" (published on its official website). It specifically mentioned that low-end privacy screen protectors are insufficient in terms of privacy protection, specifically because they mainly rely on "darkening" the screen rather than achieving privacy protection through precise angle control. Obviously, there are fundamental differences in technology and design between low-end and high-end privacy screen protectors.

Image source: giphy

The key point is that you also need to pay attention to your mobile phone usage habits. Don’t check your phone all the time. Take a 20-second break every 20 minutes and look into the distance to reduce eye pressure.

References

[1]Xu W, Yao Q, Wu P, et al. Effectiveness and visual performance assessment of anti-peeping films[J]. Displays, 2024, 82: 102669.

[2]https://huxley.media/en/roots-and-wings-with-boris-burda-olexander-smakula-from-the-ternopil-region-the-inventor-of-the-modern-technology-for-antireflection-coating/

[3] Zhao ZC, Zhou Y, Tan G, et al. Research progress about the effect and prevention of blue light on eyes[J]. International journal of ophthalmology, 2018, 11(12): 1999.

[4] https://surfshark.com/blog/privacy-screen-protectors

[5] https://www.cecopt.com/blog/does-screen-brightness-affect-eyesight.html

[6] https://iovs.arvojournals.org/article.aspx?articleid=2271352

Planning and production

Source: Bringing Science Home

Author | Su Chengyu

Editor: Yang Yaping

Proofread by Xu Lai and Lin Lin