is different. It is a phenomenon where light is reflected back to the light source with minimal scattering. If you shine a flashlight on a retroreflective surface, the light travels back toward the flashlight, making the surface appear brilliantly bright to the person holding the light, but dark to observers standing elsewhere.
No. Standard spectrophotometers measure 0°/45° or d/8 geometry, not the near-coaxial geometry required by CIE 54.2. cie 54.2
Directly from the CIE website (cie.co.at) or via national committees (e.g., IES in the US). is different
CIE 54.2 emphasizes that R’ is not a material constant—it varies dramatically with α and β. A compliant test report must list the exact geometric conditions used. CIE 54
Every reflective sign on a highway—from "STOP" to "Speed Limit 65"—should be tested per CIE 54.2. Authorities specify minimum R’ values at α=0.33° (driver’s typical observation distance) and β up to 40°.