Interpretation ID: 18121.ztv

Herr P. Binder
ITT Automotive Europe
Stuttgarter Strasse 119
74321 Bietigheim-Bissingen
Germany

Dear Herr Binder:

This is in reply to your fax of June 4, 1998, to Taylor Vinson of this Office, with respect to the use of light-emitting diodes (LEDs) in a rear lamp that ITT Automotive Europe is developing.

You have asked the factors that must be taken into consideration, the photometric requirements that must be met, "which requirements exist if one LED" fails, and which regulation will be used.

The rear lamp specifications of Federal Motor Vehicle Safety Standard No. 108 Lamps, Reflective Devices and Associated Equipment are based upon incandescent bulb technology where requirements are generally met by using one bulb for each lighted section of the lamp. The specification of 32 candela per lighted section that appear in certain SAE materials incorporated by reference in Standard No. 108 is based upon the highest output of incandescent signal lamp bulbs at the time that the SAE standards were written. When requirements are intended to be met by limited flux light sources such as LEDs, the light output specification cannot be provided by a single light source but must be provided by multiple light sources. However, current interpretations of what is necessary to comply with Standard No. 108 do not contain any differentiation based on type of light source. Thus, if 20 LEDs provide the same illumination as a single filament bulb, a lamp equipped with the former is considered a lamp with three lighted sections for purposes of compliance, not a single-section lamp. To meet the photometric requirements for three-section lamps, manufacturers must use an overly bright and costly array of LEDs.

You have asked what are the requirements if one LED fails. Failure of one light source in a taillamp or a stop lamp with more than one light source is not addressed by Standard No. 108. If a light source fails in a turn signal lamp on a vehicle that is not equipped to tow a trailer, Standard No. 108 requires that the failure be indicated to the driver. We are not aware of any LED turn signals in use, or how manufacturers would design such a unit to comply with this requirement. However, we believe that a failure should be indicated to the driver at the point where an LED turn signal ceases to furnish the minimum photometric performance required by Standard No. 108. In general, the laws of the individual states require all lamps to be fully functional on vehicles in operation but the failure of a single LED is likely to pass unnoticed.

On June 24, 1998, the agency proposed to amend Standard No. 108 to accommodate LED technology (63 FR 34350). Instead of being designed to conform to the photometric requirements based on the number of lighted sections specified in relevant SAE materials, NHTSA has proposed that a lamp equipped with LEDs that needs more than one light source to achieve compliance with the photometric performance required of a single lighted section, shall be designed to conform to photometric requirements based on the dimension of the effective projected luminous lens area for the function being tested. A lamp would be regarded as having one lighted section if the maximum horizontal or vertical linear dimension of the effective projected luminous lens area of the lamp is less than 150 mm, two lighted sections if the dimension is 150-300 mm, and three lighted sections if the dimension is greater than 300 mm.

Comments are due on the proposal not later than August 10, 1998. The proposed effective date is one year after publication of the final rule. I enclose a copy of the proposed rule for your information. We are sending this response by mail, rather than by fax, to ensure that you receive a clear copy.

Sincerely,
Frank Seales, Jr.
Chief Counsel
Enclosure
d.7/10/98
ref:108