How to Optimize LCD Cover Glass for Enhanced IR Sensor Performance

When designing applications that rely on infrared technology—be it a sleek smartphone with facial recognition or a responsive optical touch interface—a critical challenge often arises: the cover glass, meant to protect the display, can significantly attenuate the IR signal.

Orient Display FAE team is here to help!   This essay offers a clear comparison of glass types and thicknesses to guide you in selecting a solution that maximizes transmittance and ensures end-user reliability.

What is Light Transmittance of LCD Glass Cover?

Light transmittance refers to the percentage of incident light that can pass through the glass cover of a display. It is expressed in percentage (%).

Example: A transmittance of 85% means 85% of the incoming light can pass through the glass.

Factors Affecting LCD Cover Glass Transmittance

Factor	Description & Impact
Glass Type	The material composition is fundamental. Soda-lime glass, Ultra-clear glass (low-iron), and Aluminosilicate glass (e.g., Gorilla Glass) have different inherent transmittance. Low-iron glass typically offers higher transmittance.
Thickness	Thicker glass leads to greater light absorption and scattering. Thinner glass generally provides higher transmittance. For example, transmittance may increase from ~81% at 2.9 mm to ~87% at 2.0 mm for Soda-lime glass.
Surface Coating	Coatings like Anti-Glare (AG), Anti-Reflection (AR), and Anti-Fingerprint (AF) alter how light interacts with the surface. While AG may reduce it, AR coating is specifically designed to increase transmittance by reducing surface reflection.
Polarizer Attachment	Adding a polarizer changes the light’s polarization state and typically reduces overall transmittance significantly. Special “high-brightness” polarizers can recover a small amount (~1.3-1.5%).
Boarder Silk Screen Printing	Black ink printing on the borders is opaque and blocks all light. This does not affect the material’s intrinsic transmittance but reduces the effective viewable area for light transmission.

Why 940 nm Is Important in LCD Applications

While visible-light transmittance affects display brightness and clarity, the transmittance at infrared wavelengths—especially around 940 nm.

940 nm refers to the wavelength of infrared light, the transmittance of cover glass at 940 nm is critical for ensuring accurate sensor performance, Infrared light (IR) at 940 nm is widely used in proximity sensors, facial recognition, optical touch, and remote-control systems because it is safe, energy-efficient, and undetectable to the human eyes.

Many modern electronic devices integrate sensors that rely on infrared light. These components are often located behind the cover glass of displays or touch panels.

Application	Usage of 940 nm IR
Smartphone face recognition	IR illumination and depth sensing
Proximity & gesture sensors	IR reflection and detection
IR touch and in-display fingerprint	Optical transmission through cover glass
Remote controls / IR communication	940 nm IR LED
TOF (Time-of-Flight) sensors	Distance and depth mapping

For these functions to work properly, the cover glass must allow sufficient infrared light to pass through. In many specifications, a minimum IR transmittance (such as ≥80% at 940 nm) is required.

Glass Material Effect

Different glass types have different absorption characteristics for near-infrared light.

Glass Type	Transmittance at 940 nm
Standard soda-lime glass	~75–82%
Low-iron ultra-clear glass	~85–90%
Gorilla/ Dragontrail or aluminosilicate glass	~88–92%

Infrared Transmittance at 940 nm — by Glass Type & Thickness

Standard Soda-Lime Glass

Thickness	Typical IR Transmittance at 940 nm
3.0 mm	74% – 78%
2.9 mm	79% – 81%
2.5 mm	80% – 82%
2.0 mm	83% – 87%
1.1 mm	85% – 87%
0.7 mm	86% – 88%

Low-Iron Ultra-Clear Glass

Thickness (mm)	Typical IR Transmittance at 940 nm (%)
3.0 mm	84% – 87%
2.9 mm	85% – 87.5%
2.5 mm	87% – 89%
2.0 mm	89% – 91%
1.1 mm	91% – 93%
0.7 mm	92% – 94%

Aluminosilicate / Gorilla Glass/ Dragontrail

Thickness (mm)	Typical IR Transmittance at 940 nm (%)
2.9 mm	88% – 90%
2.0 mm	90% – 92%
1.5 mm	91% – 93%
1.1 mm	92% – 94%
0.7 mm	93% – 95%

Chemically strengthened aluminosilicate glass has the best infrared transmittance, making it ideal for cover glass over sensors, cameras, and biometric modules.

Comparison Summary

Glass Type	IR Performance	Strength	Cost	Typical Usage
Standard Soda-Lime	Low	Low	★	Basic cover glass, low-cost devices
Low-Iron Ultra-Clear	Medium	Medium	★★	Displays, automotive, touch cover
Aluminosilicate	High	High (chem-strengthened)	★★★	Premium cover glass, sensor window, face/fingerprint ID

Application Guidance

Use Case	Recommended Glass
Standard display cover	Standard soda-lime or low-iron glass
High-brightness display	Low-iron ultra-clear glass
Optical/fingerprint touch	Low-iron or aluminosilicate glass
Face ID / IR sensing / camera	Aluminosilicate (thin, high IR transmission)
Automotive HUD / display	Low-iron or aluminosilicate

Surface Coating Influence infrared performance differently

Coating Type	IR Impact
AR (Anti-Reflection)	Improves IR transmittance
AG (Anti-Glare)	May scatter and reduce IR
AF (Anti-Fingerprint)	Minimal effect
IR-blocking film	Blocks infrared transmission

Selecting the optimal cover glass is a strategic decision that extends beyond durability and cost. For devices featuring facial recognition, proximity sensing, or optical touch, the cover glass serves as the critical optical gatekeeper. The data presented confirms that by prioritizing high-transmittance materials—such as low-iron or aluminosilicate glass—and minimizing thickness, engineers can effectively future-proof their designs. This approach ensures robust sensor performance, unlocks new user experiences, and maintains a competitive edge in an increasingly sensor-driven market.