Standard road-marking glass beads have a refractive index around 1.5 – cost-effective and adequate for most markings. But on high-speed roads, tunnels and airport surfaces, wet-night visibility changes the requirement: water film on the line breaks retroreflection unless the bead returns light at a steeper angle. That is where higher-index beads enter the picture.
Refractive index, simply
R.I. describes how strongly the bead bends light. A bead of R.I. 1.5 returns light to the driver under normal conditions; higher-index glass (R.I. 1.7 or above) returns more light toward the source even when the bead is partly covered by water – the classic “wet-reflective” performance used for airport and expressway markings.
When standard 1.5 beads are enough
- Urban roads and parking areas with moderate speeds
- Projects where EN 1423 / AASHTO M247 Type I-II grading and budget lead
- Markings that are re-coated frequently
When to evaluate higher brightness or high-index options
- Highways, expressways and tunnels
- Airport runways and taxiways
- Rain-prone regions with night traffic
A practical middle step
Before jumping to specialty glass, many contractors first upgrade within the R.I. 1.5 family: high-brightness grades with higher retroreflectivity (RL) and tighter grading. They are a cost-effective way to lift night visibility without changing the whole specification.
Ask the right questions
- What RL value does the spec require (mcd/m2/lx)?
- Is the wet-night test part of acceptance, or only dry retroreflection?
- What size band is permitted?
Linghang supplies standard R.I. 1.5 road-marking beads plus high-brightness and high-retroreflectivity grades (RL 400-500 mcd/m2/lx class) for demanding markings; availability of higher-index grades can be confirmed against your project requirement. See our retroreflective range or ask for RL test data.