Overview
ISO 7589:2002 - "Photography - Illuminants for sensitometry" defines the spectral characteristics of standard illuminants used to evaluate photographic materials. It provides target spectral power distributions and tolerances for four ISO sensitometric illuminants: daylight (D55), studio tungsten, photoflood, and a printer illuminant for black-and-white enlarging. The standard describes how to represent these illuminants at the exposure plane (after modulation by the ISO standard camera lens) and how to assess candidate light sources for sensitometry.
Key topics and requirements
- Defined illuminants:
- ISO sensitometric daylight (photographic daylight, D55 ~5 500 K).
- ISO sensitometric studio tungsten (representing typical studio lamps with effective distribution ≈ 3 050 K).
- ISO sensitometric photoflood (modeled as a black-body at ~3 400 K).
- ISO sensitometric printer illuminant (for black-and-white paper enlarging; studio tungsten + diffuser + lens modulation).
- Spectral specification method:
- Relative spectral power distributions given at 10 nm intervals and specified as the product of source spectrum and ISO standard lens transmittance.
- Evaluation metrics:
- ISO spectral distribution index (ISO/SDI) - a three-number designation for camera films (and two-number for black-and-white papers) that quantifies how a candidate illuminant will affect photographic response relative to the ISO illuminant.
- Use of weighted spectral sensitivity tables to compute total photographic responses and SDI values.
- Acceptability and tolerances:
- Procedures and numerical tolerances for judging whether a candidate illuminant complies with the ISO aim values.
- Informative annexes:
- Examples of sources, exposure calculations, and average film/paper sensitivities.
Applications and users
ISO 7589 is used where repeatable, standardized light quality is essential in photographic testing and calibration:
- Test laboratories and manufacturers of camera films, photographic paper and sensitometers performing film speed and colour response measurements.
- Designers and calibrators of sensitometers, exposures systems, and enlargers who must match ISO spectral targets.
- Quality assurance teams in photographic production and research groups evaluating colour and black‑and‑white materials.
- Standards bodies and professionals referencing consistent procedures for sensitometry, film speed determination and illuminant validation.
Related standards
- ISO 3028 - Camera flash illuminants; determination of ISO/SDI.
- ISO 6728 - ISO standard camera lens and colour contribution index (ISO/CCI).
- ISO 7589 interacts with film speed standards and other photographic test methods that rely on standardized illuminants.
Keywords: ISO 7589, sensitometry, illuminants, photographic daylight, D55, studio tungsten, photoflood, printer illuminant, spectral distribution, ISO/SDI, camera films, black-and-white paper.
