Optical Properties of Films and Glasses Used to Protect Smartphones

Significance of the Topic

Protective films and glasses for smartphone screens combine multiple optical functions such as blue‐light reduction, privacy and scratch resistance. Accurate characterization of their transmittance and reflectance under different incidence angles is essential for product development, quality control and material selection in both consumer electronics and analytical laboratories.

Goals and Study Overview

This study demonstrates the use of a UV-VIS-NIR spectrophotometer with a variable‐angle absolute reflectance attachment to evaluate four commercial films and four glasses tailored for screen clarity, hardness, blue‐light filtering and privacy. Key objectives include determining their spectral transmittance at various angles of incidence, calculating visible light transmittance, and measuring absolute reflectance at a shallow angle.

Methodology and Instrumentation

Measurements were performed on a SolidSpec-3700DUV spectrophotometer equipped with:

• Large polarizer assembly and quartz depolarizer to minimize polarization artifacts
• Variable‐angle absolute reflectance attachment for angles from 0° to 60°
• Wavelength range 250–850 nm, 1.0 nm pitch, 12 nm slit width
• Light source switching at 310 nm and low scan speed

Visible light transmittance was calculated according to CIE daylight distribution (JIS R 3106). Absolute reflectance spectra were acquired at a 12° incidence angle.

Main Results and Discussion

• Screen clarity films and glasses exhibited the highest overall transmittance, with interference fringes observed in the film due to uniform refractive index.
• Blue‐light reduction samples showed a marked drop in transmittance and reflectance below 400 nm.
• Privacy films and glasses maintained around 50 % transmittance at normal incidence, but visible transmittance fell to about 10 % at 30° incidence.
• Reflectance for privacy films was ~3 %, while other films reflected ~7 % across the visible region.

Benefits and Practical Applications

The protocol enables:

• Objective comparison of optical performance across multiple protective products
• Optimization of coating materials for targeted functions (privacy, blue‐light blocking, hardness)
• Quality assurance in manufacturing to ensure consistent angle‐dependent behavior

Future Trends and Opportunities

Emerging directions include:

• Development of smart coatings with switchable transparency or tunable spectral filtering
• Integration of in situ angle‐resolved measurements into production lines
• Advanced modeling of multilayer interference for customized optical design

Conclusion

The study confirms that angle‐resolved UV-VIS-NIR spectrophotometry with variable‐angle reflectance capability offers comprehensive insight into the complex optical properties of smartphone screen protectors. This approach supports targeted product innovation and rigorous QC in the consumer electronics sector.

Reference

JIS R 3106: Testing method on transmittance, reflectance and emittance of flat glasses and evaluation of solar heat gain coefficient.