Interpretation ID: nht88-2.6

TYPE: INTERPRETATION-NHTSA

DATE: 04/22/88

FROM: PAUL SCULLY -- VICE PRESIDENT, PETERSON MANUFACTURING COMPANY

TO: ERIKA Z. JONES -- CHIEF COUNSEL NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

TITLE: INTERPRETATION OF "EFFECTIVE PROJECTED LUMINOUS AREA"

ATTACHMT: ATTACHED TO LETTER DATED 08/19/88 TO PAUL SCULLY FROM ERIKA Z. JONES, REDBOOK A32 (2) STANDARD 108

TEXT: Dear Ms. Jones:

The members and counsel of the Transportation Safety Equipment Institute, who met with you on April 14, 1988, requested that I send you a summary of the interpretations which industry has been using regarding the term, "effective projected luminous area" . This relates to an inquiry from Wesbar and the agency's response on the meaning of this term.

On October 28, 1970, the National Highway Safety Bureau issued the following interpretation:

"The effective projected luminous area is that area of the lens measured on a plane at right angles to the axis of the lamp, excluding reflex reflectors, which is not obstructed by an opaque object, such as a mounting screw, mounting ring, or an ornam ental bezel or trim. This allows the area of rings or other configurations (raised portions) molded in the lens to be considered part of the total effective area, even if this area does not contribute significantly to the total light output."

On October 28, 1979, an interpretation was issued by Roger Compton, Director, Office of Operating Systems, Motor Vehicle Programs, to American Motors Corporation which read as follows:

"The effective projected luminous area is that area of the lens measured on a plane at right angles to the axis of the lamp, excluding reflex reflectors, which is not obstructed by an opaque object. This interpretation allows the area of rings, or ot her configurations molded to the lamp to be considered part of the total effective area, even if this area does not contribute significantly to the total light output."

The above interpretations are basically the same. The vehicle lighting industry has been using these definitions, based on opinions from your agency, for about 18 years. Prior to that time, this same basic definition was even used by a number of indivi dual states. Also, the independent testing laboratories throughout the nation, as well as all manufacturers, have been excluding reflex areas in calculating "effective projected luminous area" for well over 40 years.

In 1987, the Society of Automotive Engineers through the SAE Lighting Committee adopted the following language which is now a part of SAE J387-Terminology:

"Effective projected luminous area" is the part of the light emitting surface measured on a plane at right angles to the axis of a lamp, excluding reflex reflectors, (but including congruent reflexes), which is not obstructed by opaque objects such as mounting screws, mounting rings, bezels or trim or similar ornamented feature areas. Areas of optical or other configurations, for example, molded optical rings or markings, shall be considered part of the total "effective projected luminous area" even if they do not contribute significantly to the total light output. The axis of the lamp corresponds to the H-V axis used for photometric requirements."

Again, you will note that the SAE term clearly excludes the reflex reflector areas. A prismatic reflex reflector is constructed to return light from an outside source. In contrast, a lens optic is designed to direct light which originates inside the le ns area. While it is true that a small amount of light escapes through the prismatic reflector area, this light cannot be controlled or directed and provides nothing more than a minimal glow of light.

I confirmed that the vehicle manufacturers in Detroit have also relied on the interpretations issued by your agency and its predecessor as described above.

The letter to Wesbar Corporation, dated March 16, 1988, appears to have been caused by a misunderstanding involving some engineering terms. We respectfully suggest a prompt clarification should satisfy everyone.

Very truly yours,