Overview
ISO 11315-1:1997, "Photography - Projection in indoor rooms - Part 1: Screen illumination test for still projectors," defines a laboratory method to measure the useful luminous flux (light output) of purely optical still projectors and the uniformity of screen illuminance in darkened projection rooms. It standardizes procedures so different projection systems can be compared reliably under reproducible conditions.
Key topics and technical requirements
- Scope: Applies to purely optical still projection (slides, overhead transparencies, episcopic images, transparent LCDs) in dark-room projection conditions.
- Photometric quantities: Focuses on screen illuminance (lux), utilised luminous flux (lumens) and uniformity ratio (g).
- Measurement grid: Screen illuminance is measured at a nine‑point grid (centre plus eight surrounding points); the arithmetic average of nine readings gives E‑avg.
- Flux calculation: Utilised luminous flux F = E_avg × A, where A is the effective projection area (w × h). The effective area shall normally be in the range 1 m² to 2 m² and be confined using a suitable mask.
- Uniformity: Uniformity ratio is defined as the ratio of the lowest to the highest measured illuminance (Emin/Emax). The standard also provides alternative corner-to-centre uniformity calculations (types 1–3) appropriate for different projector types.
- Instrumentation: Photometers must match the CIE 1931 Standard Colorimetric Observer spectral response; illuminance meters should meet CIE No. 69 class B performance. Light-sensor placement tolerance is ±20 mm from the screen plane and must be parallel to it.
- Test conditions and preparation:
- Preconditioning: projector kept in test environment for at least 8 hours.
- Ambient temperature: 23 °C ± 2 °C.
- Electrical: supply voltage and lamp current within ±0.5% of rated values; stabilization times (e.g., 20 min after switch-on when fed via ballast/transformer; 5 min for direct mains-fed lamps).
- Ambient stray light should not exceed 1% of projected illuminance; use of a black screen is recommended.
Applications and users
ISO 11315-1 is used by:
- Projector manufacturers for product specification and quality control.
- Independent test laboratories conducting photometric certification and comparison tests.
- Cinemas, lecture halls, museums and AV integrators for acceptance testing and selection of still projectors.
- Procurement and standards teams who need objective, comparable projector performance data.
Practical uses include performance comparison, acceptance testing, R&D evaluation of optical systems, and specifying minimum illumination/uniformity for presentation environments.
Related standards
- ISO 11315-2 (screen luminance test for still and video projection)
- ISO 11315-3 and -4 (projection reflecting screens and classification)
- ISO 2910 (screen luminance for motion-picture projection)
- CIE references: CIE No. 15.2 (Colorimetry), CIE No. 69 (illuminance meter performance)
Keywords: ISO 11315-1, screen illumination test, still projectors, luminous flux, screen illuminance, uniformity ratio, CIE 1931, photometer, dark-room projection.