It measures returned light at a fixed geometry.
ASTM D4956 covers retroreflective sheeting used on traffic signs. The core measurement is the coefficient of retroreflected luminance, RA, expressed in cd·lx⁻¹·m⁻²: how much light comes back to the driver per unit of illumination at the sign.
Crucially, it is measured at a defined geometry — 0.2° observation angle and −4° entrance angle for most types. That single sentence explains most specification mistakes: a film that scores well at −4° can fall by half at −30°, which is exactly the angle of a sign 7 m above a fast road.
Some types add a wide-angle test at 0.5° / −4° and a further reading at −30° entrance. Always check which geometry a quoted number refers to.
Seven types in current use, and what each is for.
If a tender quotes a type number, this is the table that tells you whether you can bid it.
| Type | Common name | Structure | White RA | Yellow RA | Typical use | Our model |
|---|---|---|---|---|---|---|
| I | Engineering grade | Glass bead | 70 | 50 | Urban signs, car parks | NVR-1000 |
| II | Super engineering | Glass bead | 140 | 100 | Guideposts, delineators | NVR-2000 |
| III | High intensity | Microprismatic | 250 | 175 | Legacy specifications | NVR-P3500 |
| IV | High intensity prismatic | Microprismatic | 360 | 270 | Highway signs, work zones | NVR-4200 |
| VIII | Wide-angle prismatic | Microprismatic | 700 | 500 | Overhead gantries | NVR-8000 |
| IX | Very high intensity | Microprismatic | 380 | 270 | Wide-angle roadside | on request |
| XI | Diamond grade | Microprismatic | 1000 | 750 | Expressway gantries, tunnels | NVR-11000 |
Minimum values from ASTM D4956-19 Table 2, white and yellow, at 0.2° / −4°. Types V, VII and X were withdrawn from the standard and are not offered. Type VI (elastomeric) is a flexible film for curved substrates and is outside the scope of this page.
Five models, five types, one lab.
All five are tested by SGS against the same clause set. The report number and issue date are on the product page — not hidden behind a form.
Three things buyers get wrong about D4956.
Each one has cost a customer a rejected shipment at least once.
Usually yes on photometrics, but not automatically on paperwork. EN 12899-1 also covers the sign substrate, the edge sealing and the manufacturer's factory production control. The film can pass RA2 and the finished sign can still fail the EN assessment — they are different scopes.
Because the standard sets a minimum, not a target. A film at 360 and a film at 430 are both Type IV. Our published figures are the ASTM minimums and our measured values run 8–12% above them — ask any supplier which of the two they are quoting.
No. Type XI is brighter at the reference geometry, but Type VIII is specified for wide-angle performance and can read better on a large overhead sign seen from close range. On a 4 m × 6 m gantry, Type VIII frequently outperforms Type XI in the driver's actual viewing cone.