ISO 20498-2:2017

Overview

ISO 20498-2:2017 specifies the light environment required for a Computerized Tongue Image Analysis System (CTIS). The standard defines optical conditions on the effective surface area where a patient’s tongue is imaged - covering illuminance, colour temperature, colour rendering, illumination uniformity, irradiance and ultraviolet (UV) irradiance. It does not cover electrical safety or biocompatibility of lighting components.

Keywords: ISO 20498-2:2017, CTIS, computerized tongue image analysis system, light environment, illuminance, colour temperature, colour rendering index, irradiance, ultraviolet irradiance.

Key topics and technical requirements

• Illuminance: 500 lx to 13 000 lx across the effective surface area.
• Colour temperature (CCT): 3 000 K to 7 000 K to control visual appearance and sensor response.
• Colour rendering index (CRI): > 90 to ensure accurate colour reproduction for diagnostic analysis.
• Illumination distribution (uniformity): ratio of minimum to maximum illuminance on the effective area must be > 0.9 (high uniformity).
• Irradiance (300–2 500 nm): total irradiance shall not exceed 350 W·m–2 (thermal/retinal/skin risk control).
• Effective UV irradiance (200–400 nm): shall not exceed 0.008 W·m–2 using the spectral weighting function in Annex A (actinic hazard assessment).
• Test methods: specifies a measuring grid (partial surfaces with centres ≤3 cm apart) and measurement procedures: illuminance meter for lux, spectroradiometer/sensor for spectral irradiance and UV, CRI measurement per CIE 013.3-1995. Sensor for irradiance measurements should have diameter ≤ 3 cm; measure at the point of maximum illuminance.

Applications and practical value

• Ensures consistent, repeatable imaging conditions for automated tongue diagnosis in Traditional Chinese Medicine (TCM) and related clinical workflows.
• Guides selection and validation of lighting systems for CTIS devices - important for manufacturers, system integrators and test labs.
• Protects patient safety by limiting thermal and photobiological exposure (irradiance and UV limits).
• Improves diagnostic reliability by enforcing high CRI and strict uniformity, reducing colour and shading artifacts that can skew image analysis algorithms.
• Useful for clinical deployment, device certification, quality assurance, and imaging protocol development.

Who should use this standard

• CTIS and medical imaging device manufacturers
• Clinical engineers, quality managers and regulatory/compliance teams
• Test laboratories and certification bodies
• Researchers developing tongue image analysis algorithms and imaging protocols
• TCM clinics adopting digital diagnostic tools

Related standards

• CIE 013.3-1995 (colour rendering measurement methods)
• IEC 62471:2006 (photobiological safety - referenced for UV weighting)
• Other parts of the ISO 20498 series (see ISO website for the full list)