Overview
ISO 5740:1982 - Road vehicles - Rear view mirrors - Test method for determining reflectance - specifies a standardized laboratory method to measure the reflectance (reflection factor) of rear view mirrors used in vehicles. Applicable to both flat and convex mirrors intended for internal and external mounting, this second edition (1982) replaces the 1978 version and defines the required apparatus, geometric conditions, spectral references and two calibration procedures.
Key topics and technical requirements
- Scope: Measurement of mirror reflectance under photopic vision conditions (CIE 1931 reference observer) for typical luminance levels.
- Reference systems: Uses the CIE calorimetric system (CIE 1931) and recommends illuminant CIE A (2 855.6 K) as the standard source.
- Apparatus:
- Light source (CIE A) with collimating optics and voltage stabilizer.
- Sample support aligned so source and receiver axes intersect at the reflective surface.
- Reflectometer with photo‑electric cell whose spectral response is proportional to the CIE photopic luminosity function.
- Optional Ulbricht sphere (integrating sphere) for total (normal + diffuse) reflection; sphere interior must be matte white and non‑selective, minimum diameter 127 mm.
- Geometric conditions:
- Incident beam preferably at 25° ± 5° to the surface normal (limit tolerance up to 30° / 0.53 rad).
- Incident beam diameter at least 19 mm; reflected beam must cover ≥50% of the detector active area.
- Calibration methods:
- Direct calibration: instrument is calibrated against incident flux (100% scale) by orienting reflectometer in axis of source; neutral density filters may be used for intermediate points.
- Indirect calibration: uses a suitably calibrated reference reflector (preferably a planar mirror with reflectance similar to test samples).
- Performance:
- Instrument linearity and electrical characteristics must preserve spectral/linearity properties.
- Reported precision: reflectometer‑indicator assembly required to achieve ±10% relative precision (on the smaller measured value basis).
Applications and users
- Automotive mirror manufacturers for product design, quality control and specification verification.
- Independent test laboratories performing reflectance certification and batch testing.
- Vehicle safety regulators specifying minimum/maximum mirror reflectance for glare and visibility control.
- Materials and coatings suppliers validating optical performance of mirror substrates and reflective coatings.
Related standards and references
- IEC/CIE Publication CEI 50(45) - vocabulary and CIE illuminant definitions referenced by ISO 5740.
- CIE Publication No. 17 (1970) - international lighting / photometry vocabulary and observer functions used in measurements.
Keywords: ISO 5740:1982, rear view mirrors, reflectance test method, reflectometer, CIE 1931, CIE A illuminant, Ulbricht sphere, direct calibration, indirect calibration, automotive mirror testing.
