Abstract:
In a preferred embodiment, an apparatus, including: a light fixture having a concave reflector disposed on a rear surface thereof; and at least one LED directed at a concavity of the concave reflector.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to light fixtures generally and, more particularly, but not by way of limitation, to a novel light fixture that is especially useful as a rear end marker for trains operating in the United States. 
     2. Background Art 
     While the present invention is described with reference to providing a rear end marking device for trains, the present invention is useful in a variety of applications. 
     In November 1977, the Federal Railway Administration (FRA) in response to a Law passed by Congress provided a Final Report covering guidelines for testing rear end marking devices for all trains operating in the United States. The Law was in reaction to a serious rear end collision where many passengers were injured and some were killed. The guidelines require a minimum of 100 candela straight on and 50 candela at plus and minus 15 degrees in the horizontal plane. The guidelines also required 50 candela at plus and minus 5 degrees straight on in the vertical plane. The maximum light level allowed is 1,000 candela. All light intensities were measured at the light source. 
     All fixtures at that time were lighted by incandescent lamps. Many of these lamps had a lamp life of 800 hours which presented a maintenance cost to the railroads because of frequent lamp replacements. The incandescent lamps also presented a safety problem, since, upon failure of an incandescent lamp, the lamp immediately becomes unlighted. With the development of LEDs having a long life, estimated in the 50,000 hour range, interest developed in creating LED rear end marker lights for trains. New lights were developed with many LEDs, perhaps as many as 50-70 LEDs facing away from the reflectors, and are now very common in traffic lights. An advantage of LEDs over conventional incandescent lamps, in addition to having a much longer life, is that, when LEDs age, they typically become darker and do not immediately become unlighted. 
     Accordingly, it is a principal object of the present invention to provide a light fixture that uses only a few LEDs. 
     A further object of the present invention is to provide such a light fixture that achieves the required oval pattern without wasting light energy in the vertical area above and below the horizontal pattern required by the FRA guidelines. 
     An additional object of the invention is to provide such a light fixture that achieve the required light beam with light energy distributed in a cone required by the guidelines in a very efficient manner. 
     Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the above objects, among others, by providing, in a preferred embodiment, an apparatus, comprising: a light fixture having a concave reflector disposed on a rear surface thereof; and at least one LED directed at a concavity of said concave reflector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figures, provided for purposes of illustration only and not intended to define the scope of the invention, on which: 
         FIG. 1  is front elevational view of a light fixture constructed according to the present invention. 
         FIG. 2  is a top plan view of the light fixture taken along line “ 2 - 2 ” of  FIG. 1 . 
         FIG. 3  is a side elevational view of the light fixture taken along line “ 3 - 3 ” of  FIG. 1 . 
         FIG. 4  is a rear elevational view of the light fixture. 
         FIG. 5  is a schematic top plan view of the light pattern produced by the light fixture of  FIG. 1 . 
         FIG. 6  is a schematic front plan view of the light pattern produced by the light fixture of  FIG. 1 . 
         FIG. 7  is a schematic side elevational view of the light pattern produced by the light fixture of  FIG. 1 . 
         FIG. 8  shows the horizontal sweep test pattern of light produced by the light fixture of  FIG. 1  at zero degrees vertical. 
         FIG. 9  shows the horizontal sweep test pattern of light produced by the light fixture of  FIG. 1  at plus five degrees vertical. 
         FIG. 10  shows the horizontal sweep test pattern of light produced by the light fixture of  FIG. 1  at minus five degrees vertical. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference should now be made to the drawing figures on which similar or identical elements are given consistent identifying numerals throughout the various figures thereof, and on which parenthetical references to figure numbers, when used, direct the reader to the view(s) on which the element(s) being described is (are) best seen, although the element(s) may be seen on other figures also. 
       FIGS. 1-3  illustrate a light fixture, constructed according to the present invention, and generally indicated by the reference numeral  20 . 
     Referring principally to  FIG. 2 , light fixture  20  includes three horizontally disposed LEDs  30  fixedly attached side-by-side to the center of an LED yoke assembly  32  and facing a parabolic reflector  34 , the middle LED disposed at the focal point of the parabolic reflector, and with the yoke assembly horizontally disposed at the center of the parabolic reflector. A housing  40  fixedly disposed on the rear surface of parabolic reflector  34  contains circuit control circuitry and drivers  42  for LEDs  30 . 
     Hermetically sealed to parabolic reflector  34  is a conventional spread lens  50  having vertical ribs, as at  52 , formed on the rear surface thereof. A gasket  60  surrounds the front of light fixture  20  and creates a waterproof seal between the light fixture and the car body lamp fixture (not shown). All other seams are sealed with silicone sealant. 
     The two off-center LEDs  30  produce beams on either side of the beam produced by the center LED, thus producing the desired energy saving oval pattern. 
     Although values and dimensions may be varied, light fixture  20  may be 5.8 inches in diameter. LEDs  30  may be 1-watt LEDs as furnished by Luxeon as Part Number LXHL-PH01. Parabolic reflector  34  may have a focal point, dimension “A”, of 1.25 inches. Lens  50  is preferably formed of red glass. Plastic may be used, but plastic even when coated is not as durable as glass. Also, lens  50  may be clear, since LEDs  30  are red, but persons are familiar with having a red lens. Screw terminal  70  is provided for attachment of a source of electrical power. 
       FIG. 4  illustrates the rear of light fixture  20  and shows screw terminals  70  which may receive 37.5- or 75-volt power, depending on the railroad car on which light fixture  20  is mounted. 
       FIG. 5  illustrates the horizontal light pattern produced by light fixture  20  and illustrates that lens  50  ( FIG. 3 ) spreads the three beams produced by LEDs  30  ( FIG. 2 ) to a relatively smooth oval pattern in the area of interest. 
       FIGS. 6 and 7  illustrate further the light pattern produced by light fixture  20 . 
       FIGS. 8-10  illustrates test data taken at horizontal sweeps at zero degrees vertical, plus five degrees vertical, and minus five degrees vertical, respectively. It can be seen from these figures that the light pattern produced by light fixture  20  is relatively uniform over the area of interest and that the light intensity is equal to or exceeds that required by the FRA guidelines. 
     By not wasting energy, this design cuts in half the power required when compared to existing designs, thereby making long hours of operation possible on the rear of freight trains. Lights on the rear of freight trains are operated from batteries which require recharging at intermittent service areas. 
     In the embodiments of the present invention described above, it will be recognized that individual elements and/or features thereof are not necessarily limited to a particular embodiment but, where applicable, are interchangeable and can be used in any selected embodiment even though such may not be specifically shown. 
     Spatially orienting terms such as “above”, “below”, “upper”, “lower”, “inner”, “outer”, “inwardly”, “outwardly”, “vertical”, “horizontal”, and the like, when used herein, refer to the positions of the respective elements shown on the accompanying drawing figures and the present invention is not necessarily limited to such positions. 
     It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.