Interpretation ID: aiam2395
Executive Vice President
Wesbar Corporation
Box 577
West Bend
WI
53095;
Dear Mr. Weber: This is in reply to your letter of September 7, 1976, asking severa questions concerning paragraph S4.4.1 of Federal Motor Vehicle Safety Standard No. 108. I am sorry that we were unable to respond by September 29 as you requested. Your questions and our answers are as follows:; '1. What is the DOT specific definition and interpretation of the word 'combined optically' as they appear in paragraph S4.4.1 of DOT 108?'; In pertinent part, S4.4.1 states that 'no clearance lamp may b combined optically with any taillamp.' The phrase 'combined optically' as used here means that the luminous area of a lens used for a taillamp may not be also used as the luminous area of a lens for a clearance lamp. In other words lamps are 'combined optically' when the same luminous area of a lens is lighted for more than a single function.; '2. Can a clearance lamp and tail lamp be combined in a singl compartment with no opaque barrier wall existing between the clearance lamp bulb and the tail lamp bulb?'; The answer is no because the same luminous area of the lens would b lighted when both lamps are in use, and the lamps would be 'combined optically.'; '3. Does the DOT have no objection to a flashing red signal issuin from the side (at right angles to the fore-aft center line of the trailer) of the clearance lamp?'; Generally S4.6(b) requires most vehicle lamps to be steady burning i normal operation. If the right angle lamp serves as the rear side marker lamp, however, S4.6(b) allows it to be flashed for signaling.; '4. What is the DOT specific definition and interpretation of the ter 'clearance lamp' as it is used in DOT 108?'; The term 'clearance lamps' is defined by SAE Standard J592e incorporated by reference in Standard No. 108, and are 'lamps which show to the front or rear of a vehicle. . . to indicate the overall width and height of the vehicle.'; '5. Does the 'clearance lamp' as the words are used in DOT 108 indicat a lamp intended to serve as its major function, a back up lamp in the event of failure of the tail light filament in the combination tail, turn and stop light bulb.'; There is no intent that a clearance lamp serve as a back-up lamp in th event of a taillamp filament failure though obviously both lamps perform a marking function.; '6. If DOT approves the combination of a clearance lamp and tail lam in the same compartment, would it also approve for a boat trailer, moving the tail light outboard to show the extreme width of an over 80 foot vehicle and eliminate the need for a clearance lamp under those circumstances.'; The question is moot since a combination clearance lamp-taillamp is no permitted.; I understand that you discussed the photometric test procedure fo optically combined lamps with Mr. Owen of this agency, by telephone on September 22, 1976. So that there may be no misunderstanding I would like to set forth the test procedure in this letter. If a single lamp bulb (or filament) is used in the combined lamp, the photometrics for all of the functions must be met simultaneously. If two or more lamp bulbs (or filaments) are used and each is to provide a separate function, only those which provide that function are to be energized during the photometric test. Therefore, in a multiple compartment side marker and clearance lamp (or a multiple compartment tail and clearance lamp that is not optically combined), the clearance lamp bulb is not energized during the photometric test for the other function, and vice versa.; I hope this answers your questions. Sincerely, Frank A. Berndt, Acting Chief Counsel