THE CHARACTERIZATION OF AUTO HEADLIGHT GLASS BY REFRACTIVE INDEX AND DENSITY

This study was designed to evaluate the potential usefulness of measurements of refractive index (RI) and/or density of automotive headlight glass for forensic purposes. Automotive headlights were obtained from several sources. As of the time the analytic work was performed, it appeared that there were three subpopulations of headlight glass: General Electric (GE), Corning manufactured before 1971, and Corning manufactured after 1971. The distributions of RI (and density) for the first two subpopulations overlapped considerably, so that one could not reliably determine to which of these a candidate piece of glass belonged. However, the latter population was different enough that one could reliably classify a fragment as belonging either to one of the first two or to the third. Furthermore, since headlights on the road at that time were about equally split between the three groups, the performance of both RI and density for individualization (i.e., the matching of an unknown fragment with a specific lens) was evaluated using the fact of an even split. Since the analytical work was done, the composition of glass has been changed several times by both manufacturers (and a significant number of lenses not made in the United States have appeared on the road). Without another comprehensive sampling of lenses, it is not possible to know how different the lenses on the road today really are. However, one may obtain a conservative figure by acting as though there is only one population, and this is done in section 9 (which updates the report to January 1981).

• Corporate Authors:

  National Bureau of Standards

  Law Enforcement Standards Laboratory
  Washington, DC  United States  20234

  Department of Justice

  National Institute of Justice
  Washington, DC  United States  20531
• Publication Date: 1981-10

Media Info

• Pagination: 37 p.

Subject/Index Terms

• TRT Terms: Density; Forensic medicine; Forensic science; Glass; Headlamps; Materials selection; Refractivity
• Subject Areas: Highways; Vehicles and Equipment; I91: Vehicle Design and Safety;

Filing Info

• Accession Number: 00367618
• Record Type: Publication
• Source Agency: National Highway Traffic Safety Administration
• Report/Paper Numbers: NBSIR 81-2286 Final Rpt., HS-033 074
• Files: HSL, TRIS, USDOT
• Created Date: Sep 30 1982 12:00AM