Overview
ISO 23364:2021 - "Optics and Photonics - Bulk absorption optical filters" standardizes how uncoated bulk absorption filters are specified, measured and described for optical applications (excluding ophthalmic spectacles). It defines functional filter types, key optical parameters and the required test/measurement conditions for both raw materials (filter glass, filter plastics) and finished polished components. The standard does not specify material internal quality, manufacturing processes or coated filters (see ISO 9211 series for coated optics). Note: additional optical effects can arise in high-power applications.
Key topics and technical requirements
- Filter functions and classification - Defines bulk absorption filter types by their functional spectral behaviour (e.g., neutral density/attenuating, bandpass, bandreject, shortpass, longpass).
- Optical parameters - Formalizes spectral quantities such as:
- Spectral transmittance τ(λ) and spectral internal transmittance τi(λ)
- Cut-off wavelength (λ0.5) where transmittance = 0.5
- Spectral optical density D(λ) and spectral extinction/absorbance E(λ)
- Spectral diabatic transmittance θ(λ) and luminous transmittance τV for specified illuminants
- Measurement boundary conditions - Specifies default measurement geometry (normal incidence, angle of incidence = 0°), witness sample concept, and the role of thickness d in path length and internal transmittance.
- Test and measurement methods - Provides rules for measurement conditions, numerical specification and graphical representation of spectral characteristics (see clauses on measurement and Section 5 on numerical/graphical rules).
- Representation rules - Establishes standardized ways to report spectral curves, cut-off wavelengths and peak transmittance values to ensure unambiguous specifications between suppliers and users.
Practical applications and users
ISO 23364:2021 is relevant to:
- Optical component manufacturers and glass/plastic filter producers specifying bulk absorption filters
- Systems integrators and instrument designers in imaging, spectroscopy, sensing, laser optics and general photonics where uncoated filters are used
- Test laboratories performing spectral measurements and quality checks on filter witness samples
- Procurement and quality teams requiring standardized filter specifications for comparison and acceptance
This standard helps ensure consistent communication of spectral performance (transmittance, optical density, cut-off) and reproducible measurement practices across the optics and photonics supply chain.
Related standards
- ISO 9211 series - optical coatings (for coated filter alternatives)
- ISO 11664-1 / ISO 11664-2 - colorimetric parameters and luminous transmittance (referenced for τV and colorimetric descriptions)
Keywords: ISO 23364:2021, bulk absorption optical filters, spectral transmittance, optical density, optics and photonics, filter specification, witness sample, cut-off wavelength, test methods.
