FMVSS #108 … and Common Sense … mandates that traffic directly following and adjoining must be exposed to fairly Contiguous, Large Lit Up Areas of properly directed “Light Rays” in order for adequate Brake, Turn and Lane Changing signal responses.


Federal Law mandates that single Brake and Turn Signals used on all Over 80” Wide Vehicles must have an “EPLLA” of at least

11-5/8 in² as required by SAE J1398 – ‘85*.  The mandated Brake/Turn Signal “EPLLA” is reduced to 7-3/4 in² for Under 80” Vehicles specified by SAE J586 FEB ‘84* and the 1994 Section § addition.  EPLLA mandates have been neglected for the past few years and NHTSA has recently tried to more clearly define and verify EPLLA importance in their 2005 “Rewrite” of FMVSS #108 (Docket No. NHTSA-2006-23634).     *Check out “SAE” Specs and compare with the Federal, “Definitions” stated below:


Referring to the “Definition” Quotes from FMVSS #108:

§ 571.108 Standard No. 108; Lamps, reflective devices, and associated equipment


Effective light-emitting surface means that portion of a lamp that directs light to the photometric test pattern, and does not include transparent lenses, mounting hole bosses, reflex reflector area, beads or rims that may glow or … produce small areas of increased intensity as a result of uncontrolled light from an area of 1/2 degree radius around a test point.


Effective projected luminous lens area means the area of the orthogonal projection of the effective light-emitting surface of a lamp on a plane perpendicular to a defined Test Pattern direction relative to the axis of reference.  Unless otherwise specified, the direction is coincident with the axis of reference.            


§ 571.108 … Section S6.3 The term ‘‘functional lighted lens area’’ in any SAE Standard or Recommended Practice incorporated by reference or by subreference in this standard, has the same meaning as the term ‘‘effective projected luminous lens area.’’



Note! That “EPLLA” … for Under 80” Vehicles … was increased from 5¾ in² to 7¾ in² by the below 1994 FVMSS #108 addition:

§ Section … On a motor vehicle whose overall width is less than 80 inches:

(a)  The effective projected luminous lens area of a single compartment stop lamp and a single compartment rear turn signal lamp, shall be not less than 50 square centimeters (7¾ square inches).


Unfortunately, the above Definitions and the terms Effective Light Emitting Surface and Effective Projected Luminous Lens Area” (“EPLLA”)are rarely understood by OEM Designers and Aftermarket Buyers.


Below, I’ve “tried” to write a couple of “clarifying paragraphs” … explaining the term “Effective Projected Luminous Lens Area” using my humble vocabulary, which hopefully makes the “EPLLA” mandates easier to visualize and understand!


Imagine the usable light output (“Rays”) from any source of Illumination (Bulbs or LEDs), which are directed thru a Fresnel Lens or are simply Reflected and/or Refracted using any combination of Reflective/Refractive Faceting, which results in specific, seeable, lit-up areas that are effectively projecting “controlled” and distinguishable rays of light, within the mandated “Test Pattern” … of 20° Left/Right; 10° Up/Down … but not beyond.


All the “Lit Facet Surface Areas” of a Test Lamp that are compliant to the official FMVSS #108 EPLLA Definition can be “officially tallied” towards meeting the mandated “EPLLA” requirements of FMVSS #108.  If the total of all qualifying Lit Facet Surface Areas (pointing straight out) add up to at least 11-5/8 in² … the Test Lamp can, legally, be used as a Single, Brake or Turn Signal” on any Over 80”, or Under 80”, width Vehicle.  However, if only 7-3/4 in² (or under) … then the Lamp can be used for Single, Brake/Turn Signals on only, Under 80” vehicles.  If the Lamp has an “EPLLA” total below 7-3/4 in² … it does not legally qualify for any U.S.A., or Canadian mandated Single, Brake or Turn Signal use, except perhaps, for 3rd Brake Light (CHMSL) or Motorcycle uses.


Always keep in mind when tallying up officially qualifying “EPLLA”you must disregard all “Faked”, “Non-Operative”,  “Misdirecting & Transparent Areas”, that are producing small areas of increased intensity as a result of uncontrolled light”.*

               *Quote from above Definition


Also, as you can witness in real-life observations … to be compliant to mandated “EPLLA” requirements … it will take many standard 20° Conal Output LEDs - not just a few … to meet “EPLLA” requirements for a single Brake and Turn (Lane Change) Sized. 

See TLC 111B for more details

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