Did you know? Retroreflection is different to reflection because it reflects light back in the same direction, unlike reflection which mirrors the image.
For most vehicles, the number plate is the only retroreflective surface. As such, it is a key safety feature and tightly controlled by the standard.
How are plates tested?
The standard says that the plate’s background and digits must have very different retroreflectivity limits; 150 units vs 0.5 units respectively. These units are measured at 6 different angles in total; left and right 5°, 30° and 45°.
The sample is then also wetted and tested at a number of angles again.
Measurements within range will mean the right contrast for both the human eye and ANPR cameras.
What makes a fail?
- Dry plates: a loss of retroreflection more than 20%.
- Wet plates: a loss of retroreflection more 28%