ISO 18937-2:2023

Overview

ISO 18937-2:2023 specifies laboratory methods for measuring the indoor light stability (lightfastness) of photographic materials using a filtered xenon‑arc lamp. It covers test equipment, filters, exposure conditions (irradiance/illuminance), temperature and relative humidity control, and measurement/reporting procedures for colour and monochrome reflection prints, transparent/translucent films, photobooks and prints for backlit displays. The procedures simulate two common end‑use scenarios: general indoor display (indirect, window‑filtered daylight in homes) and simulated in‑window display (terrestrial daylight transmitted through architectural double glazing).

Key technical topics and requirements

• Light source and filters
  • Quartz‑jacketed xenon‑arc lamps emitting UV through IR; optical filters remove short‑wavelength UV to reproduce target spectral irradiance.
  • General indoor test uses window‑glass filters plus a UV cut‑off filter with 50% transmittance at 370–375 nm (examples: L‑37, SC‑37).
• Spectral irradiance
  • Relative spectral bands are prescribed (e.g., minimal energy below 340 nm; majority between 430–800 nm) to match indoor daylight characteristics.
• Exposure control parameters
  • Illuminance at specimen plane: up to 80 klx (alternatively irradiance measured at 420 nm).
  • Black‑panel temperature target: 25–35 °C (uninsulated); chamber air 21–27 °C; relative humidity typically 50% RH.
  • Option to use IR‑reducing filters to meet temperature setpoints.
• Apparatus and measurements
  • Requirements for radiometers/illuminance meters, black‑panel thermometers, humidity sensors and inert exposure chambers.
  • Irradiance uniformity in the exposure area must be at least 80% of maximum (periodic specimen repositioning may be required).
  • Measurement of irradiance/illuminance, radiant exposure, and pre/post exposure colorimetric or densitometric changes.
• Test specimen handling
  • Conditioning, mounting, backing/open framing and sampling follow guidance in ISO 18937‑1.

Practical applications and users

• Use cases:
  • Comparative lightfastness testing for photographic papers, films, photobooks and backlit prints.
  • Product quality control, R&D for imaging materials and inks, and specification verification for display applications.
  • Conservation assessment and lifetime estimation of displayed photographic collections.
• Primary users:
  • Material manufacturers, print labs, independent testing laboratories, museums and archives, conservators, and standards bodies.

Related standards

• ISO 18937‑1: General guidance and requirements for indoor light stability testing
• ISO 18913: Imaging materials - Permanence - Vocabulary
• ISO 9370: Radiant exposure determination in weathering tests

Keywords: ISO 18937-2:2023, xenon‑arc lamp exposure, indoor light stability, photographic prints, lightfastness, simulated in‑window display, illuminance, irradiance, photobook testing.