Dr. Wayne W. Tennesey
Testlabs International Ltd.
1797 Logan Avenue
Canada R3E 1S9
Dear Dr. Tennesey:
This responds to your inquiry regarding the luminous transmittance requirement in Federal Motor Vehicle Safety Standard (FMVSS) No. 205, Glazing Materials. You believe and are concerned that handheld spectrophotometer devices which are used in law enforcement in Canada to determine the percentage of incident light transmitted through vehicle windows may return different results for the same sample.
Reliable test results are a crucial part of any test program, and the National Highway Traffic Safety Administration (NHTSA) carefully assesses compliance with the luminous transmittance requirement of FMVSS No. 205 in a manner that provides accurate results. The test that we use is described below. To the extent that you are concerned about the reliability of devices used by localities, your concern should be addressed to the jurisdictions involved.
By way of background, NHTSA is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment. NHTSA enforces compliance with the standards by purchasing and testing vehicles and equipment, and we also investigate safety-related defects. The agency has established FMVSS No. 205 (49 CFR 571.205), which specifies performance and marking requirements for various types of glazing. FMVSS No. 205 incorporates by reference American National Standard for Safety Glazing Materials for Glazing Motor Vehicles and Motor Vehicle Equipment Operating on Land Highways-Safety Standard ANSI/SAE Z26.1-1996 (ANSI Z26.1).
ANSI Z26.1 specifies that glazing at specific locations shall have at least 70 percent luminous light transmittance, at normal incidence (i.e., with the glazing perpendicular to the measuring device), when measured in accordance with Luminous Transmittance, Test 2 of ANSI Z26.1. Paragraphs 5.1 and 5.2 of Luminous Transmittance, Test 2, specify the sample sizes that are used for the test, the light source to be used, and how to interpret the results. Paragraph 5.1.2 of ANSI Z26.1 states that three specimens of glazing shall be tested for
regular luminous transmittance at normal incidence calculated to International Commission on Illumination Illuminant A. The standard further specifies that after the regular luminous transmittance has been determined, the same three specimens shall be subjected to ultraviolet radiation (irradiation), and specifies the lamps that can be used for this irradiation. Paragraph 5.2.3 of ANSI Z26.1 specifies that glazing subject to Luminous Transmittance, Test 2 shall show regular luminous transmittance of not less than 70 percent of the light, at normal incidence, both before and after irradiation. The international standard ISO 3538-1978, Road Vehicles Safety glasses Test methods for optical properties (referenced in section 2.4 of ANSI Z26.1) provides the requirements to be found in equipment to be used for the transmissibility determination.
NHTSA safety standards apply to the manufacture and sale of new motor vehicles and motor vehicle equipment. 49 U.S.C. 30112. In the U.S., States regulate the operation (i.e., use) of motor vehicles, and many limit how darkly tinted the glazing may be in vehicles operating in their jurisdictions. It appears that your question relates to the manner in which some Providences are enforcing their luminous transmittance requirements, and thus should be addressed to and answered by the entity that you believe uses an unreliable handheld device. We are not in a position to render an opinion on the means by which a Providence should resolve a disputed test result of a handheld spectrophotometer unit.
If you have any further questions, please feel free to contact Sarah Alves of my staff at this address or by telephone at (202) 366-2992.
Stephen P. Wood
Acting Chief Counsel