When navigating the vast array of screen protectors, you might wonder:
“Why do some screen protector look yellowish while others are crystal clear?”
“Is 9H the hardest rating?”
“Do thinner screen protector feel better, but thicker ones last longer?”
These experiences hinge on three key factors: light transmittance, hardness, and thickness. Let’s dive into their relationship and guide you toward selecting the ideal screen protector.
Light Transmittance
Light transmittance refers to the amount of light that passes through the screen protector. A high transmittance level—around 92% or more—ensures the screen appears bright with accurate colors. In contrast, those screen protectors with transmittance below 88% may cause the display to look dim, grayish, or yellowish, which can reduce comfort during prolonged use.
The main factors affecting transmittance are the material and manufacturing process. Tempered glass screen protector typically offers excellent clarity, making it the top choice for high-definition screen protectors. TPU and EPU protectors are more flexible, but generally offer lower optical clarity.
Surface treatments like anti-glare or matte finishes also influence light transmission. To achieve effects like blue light filtering, eye protection, or privacy, some screen protectors add extra coating layers. These layers tend to reduce overall transmittance slightly due to increased light absorption.
While it isn’t the primary factor in light transmittance, thicker protectors can increase internal light loss through absorption and reflection. That’s why it’s important to strike a balance between thickness and optical performance when choosing a screen protector.
If you need a clear screen—for example, if you’re a photographer, designer, or gamer—it’s best to select a glass screen protector with at least 92% light transmittance. For eye protection, blue light filtering protectors are a good choice (they might slightly change the screen color, but they help reduce eye strain). If privacy is your main concern, a privacy screen protector can block side views, though it will make the screen look a bit dimmer.
Hardness
Hardness describes resistance to surface damage such as scratches, dents, or abrasions. For screen protectors, it indicates how well the surface can stand up to everyday wear—like contact with keys, coins, or dust particles.
Screen protector hardness is usually measured using the Pencil Hardness Test. This involves applying pencils of different hardness levels (ranging from 6B to 9H) to the surface at a consistent angle and pressure. A “9H” rating means the protector can resist scratches from a 9H pencil—the hardest pencil in the test. However, this doesn’t mean the protector is completely scratch-proof or comparable to minerals on the Mohs hardness scale.
Is Greater Hardness Always Better?
While higher hardness generally means better scratch resistance, it’s not without trade-offs. As hardness increases, the material's flexibility—its toughness—tends to decrease. In practical terms, ultra-hard screen protector is more brittle and more likely to crack or chip on impact, especially around exposed edges not covered by a case.
Some ultra-hard screen protectors may also interfere with under-display fingerprint sensors, particularly those using ultrasonic technology. Additionally, harder screen protector can feel overly “crisp” or stiff to the touch. Tapping on it may produce a sharp, high-pitched sound, which can be less pleasant than the feel of a protector with a bit of cushioning.
While increased thickness can improve impact resistance to some degree, it doesn’t directly enhance surface hardness.
Thickness
In the screen protector industry, there are several commonly used thickness options:
0.26 mm: A very thin option that delivers excellent touch sensitivity and clear display quality, though it offers less protection against drops or impacts.
0.33 mm: The most widely used thickness, striking a good balance between durability, touch responsiveness, and overall fit.
0.4 mm: A thicker choice designed for better impact protection, but it may slightly affect touch performance or make the protector harder to fit with certain phone cases.
Most users prefer 0.26 mm–0.33 mm tempered glass for a balance of protection and usability.
Practical Considerations When Choosing Screen Protector
Light transmittance, hardness, and thickness are all key factors in a screen protector. They influence each other and are all essential—none can be ignored. When choosing a protector, it’s important to think about which factor matters most to you.
