ISO 7591 Retro-Reflective Registration Plates for Motor Vehicles and Trailers - Technical Specifications

The "ISO 7591 Road vehicles - Retro-reflective registration plates for motor vehicles and trailers - Technical specifications" standard, published by the International Organization for Standardization (ISO), describes the provisions applicable to registration plates. Compliance with national regulations in terms of dimensions, shape, letters, and numbers is checked by the competent authorities on a fully finished plate. This standard includes photometric and colorimetric properties for both day and night. It defines sampling and various testing methods.

Retro-reflective license plates are vehicle license plates that use a special reflective material designed to reflect light back to its source. This makes the plate highly visible when illuminated by headlights at night.

Unlike ordinary painted license plates, retro-reflective license plates contain a reflective layer made of tiny glass beads or microprisms. These optical elements redirect incoming light back toward the emitting vehicle or camera, significantly improving visibility.

When a car's headlights hit a retro-reflective license plate:

• Light strikes the reflective surface.
• Glass beads or microprisms within the reflective layer redirect the light.
• Most of the light reflects back towards the headlights (light source).
• The license plate appears bright and easy to read, even from a considerable distance.

A typical reflective plate consists of the following:

• Protective transparent film: Provides protection against UV rays, weather conditions, and scratches.
• Reflective layer: A layer containing glass beads or microprisms.
• Printed background: Usually white or yellow, depending on national regulations.
• Registration characters: Black or another contrasting color.
• Metal or plastic substrate: Provides structural integrity.

There are two main technologies:

• Glass bead technology: Uses millions of microscopic glass spheres. It is mature and cost-effective. It is common in many traditional reflective materials.
• Microprismatic technology: Uses small prism-shaped structures. Provides higher reflectivity. Improves long-distance visibility. Generally has a longer service life.

The ISO 7591 standard enhances vehicle identification and road safety by ensuring license plates remain clearly visible in both daytime and nighttime conditions. The primary purpose of this standard is to define the technical specifications that retro-reflective license plates must meet. Rather than defining national plate sizes, numbering systems, or fonts, this standard focuses on the optical and physical performance of the finished license plate.

This standard helps license plates ensure the following:

• They are easily readable both during the day and at night.
• They provide consistent retro-reflective performance when illuminated by vehicle headlights.
• They must retain their appropriate color properties.
• They must withstand environmental influences during normal use.
• They provide reliable performance regardless of the country of manufacture.

The ISO 7591 standard applies to retro-reflective license plates used on the following vehicles:

• Passenger cars
• Commercial vehicles
• Buses
• Trucks
• trailers

This standard applies specifically to the finished license plate and its reflective surface. National authorities are responsible for the following requirements:

• Plate dimensions
• Character size
• Font style
• Numbering formats
• Vehicle registration regulations

Compliance with these regulatory requirements is verified separately by the relevant government agency.

The basic requirements are determined as follows:

• Retro-reflective performance: One of the most important requirements is measuring the retro-reflection coefficient, which determines how effectively the plate reflects light back to the source. A compatible plate should provide the following:
  • It should produce sufficient brightness when illuminated by vehicle headlights.
  • It must maintain visibility from various viewing angles.
  • It must continue to provide adequate reflection throughout its service life.

These features allow police officers, toll booths, traffic cameras, and other drivers to identify vehicles during nighttime operations.

• Color measurement requirements: The ISO 7591 standard specifies acceptable daytime and nighttime color characteristics. The reflective material must provide the following:
  • Suitable white background appearance
  • Consistent color borders
  • Stable chromatic properties
  • Uniform visual appearance

Proper color control improves readability and prevents confusion in varying lighting conditions.

• Physical structure: This standard requires the completed registration plate to have sufficient mechanical strength. Typical performance characteristics include:
  • Good adhesion of reflective materials.
  • Resistance to peeling
  • Dimensional stability
  • Uniform surface finish

These features help maintain readability throughout the plate's service life.

• Sampling and testing: The ISO 7591 standard describes the sampling procedures and testing methods used to verify compliance. Typical assessments include:
  • Photometric measurements
  • Color measurements
  • Visual inspection
  • Material performance verification

Tests are performed on completed registration plates instead of individual raw materials.

ISO 7591 standard tests generally evaluate the following:

• First retro-reflective brilliance
• Reflective performance at the specified viewing angles.
• Daytime color values
• Night visibility
• Homogeneity of the reflective coating.
• Surface quality
• Post-production compatibility

Manufacturers can also conduct additional environmental durability tests to meet regional regulations.

The ISO 7591 standard is used in the automotive and transportation sectors by:

• License plate manufacturers
• Manufacturers of reflective sheets.
• State vehicle registration offices
• Vehicle inspection authorities
• Automotive regulatory bodies
• Traffic enforcement agencies

It also supports suppliers of reflective materials used in vehicle identification systems.

Implementing the ISO 7591 standard offers several advantages:

• Improving the visibility of vehicle license plates at night.
• Improving road safety through reliable vehicle identification.
• Consistent production quality across different suppliers.
• Improved compatibility with automated monitoring systems.
• Reliable performance in varying environmental conditions.
• International consistency for manufacturers serving multiple markets.

The ISO 7591 standard complements, rather than replaces, national vehicle registration laws. Countries generally set their own requirements regarding the following:

• Registration number format
• Plate dimensions
• Security features
• Fonts
• Country identifiers
• Reflective graphics

This standard allows each country to maintain its own registration system while providing a common technical basis for reflective performance.

The ISO 7591 standard is particularly important for the following sectors:

• Automotive production
• Highway transports
• Vehicle registration authorities
• Law enforcement agencies
• Highway administrations
• Intelligent transportation systems
• Traffic monitoring equipment manufacturers

In conclusion, the ISO 7591 standard is a significant international standard for the performance of retro-reflective vehicle registration plates. By defining reflectivity, color, durability, and testing requirements, it helps ensure that plates remain visible and legible in both daytime and nighttime conditions. While it does not regulate the appearance or numbering of the plates, it establishes internationally accepted quality criteria that support road safety, traffic control, and reliable vehicle identification worldwide.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the ISO 7591 standard.