ISO 3538:1997

Overview

ISO 3538:1997 defines standardized test methods for the optical properties of safety glazing materials used in road vehicles. It covers procedures to evaluate luminous transmission, secondary image separation and optical distortion for any type of safety glazing (glass or other materials). The standard sets environmental test conditions, measurement apparatus characteristics and reporting formats so manufacturers, test labs and regulators can assess glazing performance consistently.

Key topics and requirements

• Scope and definitions: Clear definitions for terms such as optical angular deviation, optical distortion, luminous reflectance, CIE standard illuminant A and the CIE 1931 standard observer are provided to ensure consistent interpretation.
• Test conditions: Default environmental conditions are specified (temperature, pressure and relative humidity) to ensure repeatable results.
• Regular luminous transmittance: Procedure and apparatus (CIE A-type light source, collimated beam using lenses and diaphragms, detector with spectral responsivity matching the CIE photopic efficiency) to measure transmitted light fraction.
• Secondary image separation: Two methods for detecting ghost/secondary images:
  • Target test - viewing an illuminated ring or ring-and-spot target through the glazing at a prescribed observation distance (typically several metres).
  • Collimation telescope test - optical system forming a polar coordinate image; secondary image separation read directly in the focal plane.
• Optical distortion test: Project a high-contrast raster (array of circles) through the glazing and measure the change in projected image geometry. ISO 3538 describes projector arrangement, slide quality, scanning/support stands, and options for photoelectric measurement or strioscopic techniques. The standard gives methods to convert measured changes in projected image size to angular distortion metrics.
• Apparatus accuracy and detector requirements: Linearity and spectral response limits for detectors, focal length and aperture guidance for lenses, and integrating sphere alternatives when applicable.
• Alternative and quick-assessment methods: Templates and simpler “Go/No‑Go” target designs are allowed where rapid or less-precise checks suffice.

Applications and users

• Vehicle manufacturers and component suppliers validating windshield and glazing optical quality.
• Independent test laboratories performing type approval, quality control and conformity testing.
• Safety engineers assessing driver visibility, glare, ghost images and distortion impact on driving comfort and safety.
• Regulatory bodies and certification agencies establishing compliance with vehicle glazing requirements.

Related standards

• References to CIE documents (CIE standard illuminant A, CIE 1931 standard observer) and related ISO road‑vehicle standards (see ISO publications cited in the clause notes) are used to define light sources and observers for measurement.

Keywords: ISO 3538, safety glazing, road vehicles, optical properties, luminous transmittance, secondary image separation, optical distortion, glazing test methods.