ISO 23946:2020

Overview

ISO 23946:2020 specifies a standardized test method using a gonio-spectrofluorometer to measure optical properties of ceramic phosphor powders used in white light-emitting diodes (LEDs). The standard covers absolute measurement procedures for internal quantum efficiency (IQE), external quantum efficiency (EQE), absorptance, luminescent radiance factor, and relative fluorescence spectrum of phosphors that emit visible light when excited by UV or blue light. ISO 23946 complements integrating-sphere methods (see Related Standards) by providing angle-resolved, goniometric evaluation suitable for ceramic phosphors and high-performance solid-state lighting (SSL) applications.

Key Topics and Requirements

• Measurement principle: Use of a gonio-spectrofluorometer to record angle-dependent spectral distributions of scattered and fluorescent light under monochromatic excitation.
• Coordinate system: Spherical coordinates (angle of incidence, zenith and azimuth angles) and definitions for in-plane and out-of-plane measurements.
• Apparatus components: Light source unit, sample cell and stage, diffuse reflectance standard, directing optical system, spectrometer/detector, amplifier, rotational positioning mechanisms, enclosure, and data processing unit.
• Calibration and maintenance: Wavelength calibration, spectral responsivity calibration, verification of diffuse reflectance standards, and positional accuracy of rotational units.
• Sample preparation: Storage, pre-processing, and cell filling procedures for ceramic phosphor powders to ensure repeatability.
• Measurement procedures: Environment control, in-plane/out-of-plane goniometric scans, azimuthal variation, surface uniformity evaluation, and handling of less-absorptive samples (informative annex).
• Calculations and outputs: Corrections for spectral responsivity and accumulation time, conversion to photon-number spectral distributions, calculation of scattered and fluorescence photon numbers, interpolation at dead angles, and final IQE, EQE, absorptance and luminescent radiance factor reporting.
• Reporting: Required test-report elements to ensure traceability and reproducibility.

Applications and Who Uses It

• Phosphor manufacturers - to quantify and compare IQE/EQE and absorptance for product development and specification sheets.
• LED and lighting OEMs - to evaluate phosphor performance for color quality, efficiency and thermal management in white LEDs.
• Materials and optical test laboratories - for accredited measurements, quality control and inter-laboratory comparisons.
• R&D teams - to optimize phosphor formulations, particle microstructure and ceramics processing for high-performance SSL.
• Regulatory and standards bodies - to harmonize methods for photoluminescence and goniometric optical characterization.

ISO 23946 enables robust, angle-resolved optical characterization that supports competitive LED product development, reliable quality assurance, and consistent measurement practices across the lighting industry.

Related Standards

• ISO 20351 - Absolute measurement of internal quantum efficiency of phosphors using an integrating sphere (complementary method).
• CIE S 017/E - International Lighting Vocabulary (terminology referenced).