Optical Properties of Films and Glasses Used to Protect Smartphones

Significance of the Topic

The increasing demand for smartphone screen protectors with specialized functions such as privacy shielding, blue light reduction, enhanced hardness and clarity has created a need for precise optical characterization methods.

Objectives and Study Overview

This study evaluates the optical performance of four commercial protective films and four glass screen protectors. A UV-VIS-NIR spectrophotometer equipped with a variable angle absolute reflectance attachment was used to measure spectral transmittance at multiple incident angles and absolute reflectance at a shallow angle.

Methodology and Instrumentation

Samples were grouped by functional design: privacy, hardness, blue light filtering and clarity. Spectral measurements covered 250 to 850 nm with 1 nm resolution and low scan speed. Transmittance was recorded from 0° up to 60° incidence, while absolute reflectance spectra were acquired at 12° incidence. A polarizer and a quartz depolarizer were used to remove polarization effects.

Used Instrumentation

• Spectrophotometer: Shimadzu SolidSpec-3700DUV
• Attachment: Variable angle absolute reflectance unit with large polarizer assembly
• Wavelength range: 250–850 nm
• Slit width: 12 nm
• Sampling pitch: 1.0 nm
• Light source switching at 310 nm

Main Results and Discussion

• Clarity films exhibited the highest and most uniform visible transmittance across the measured range.
• Blue light reduction films showed a progressive decline in transmittance below 600 nm.
• Privacy films provided approximately 50 % transmittance at normal incidence; visible transmittance dropped to about 10 % at 30° incidence, confirming the privacy effect.
• Glass protectors for privacy and hardness shared similar transmittance curves, while blue light glass experienced a notable drop below 400 nm.
• Privacy films and glasses showed low absolute reflectance (~3 % and ~5 % respectively); other samples measured around 7 % reflectance.
• Interference fringes in clarity films indicate multilayer structures and differing refractive indices compared to hardness films.

Benefits and Practical Applications

These spectral analyses enable manufacturers and quality-control laboratories to verify that protective films and glasses meet design criteria for privacy, eye safety and mechanical durability. Optimizing coating composition and layer architecture relies on such precise measurements.

Future Trends and Opportunities

Emerging developments include adaptive smart coatings with tunable transmission, integration of nanostructured filters, and predictive modeling of optical performance. Potential applications span foldable displays, augmented-reality interfaces and energy-efficient smart windows.

Conclusion

The SolidSpec-3700DUV with variable angle absolute reflectance capability offers a robust and versatile approach to characterize the nuanced optical properties of smartphone protective films and glass, supporting product innovation and quality assurance.

References

1. JIS R 3106: Testing method on transmittance, reflectance and emittance of flat glasses and evaluation of solar heat gain coefficient.
2. Shimadzu Application News Nos. A390 and A394: Details on variable angle absolute reflectance attachments.