Abstract:
A compact warning light employs LED lamps as a light source and has a lighthead configured for insertion into the reflector shells of a motor vehicle such as a sedan or SUV. The lighthead has a base and cover which define a sealed interior space surrounding the LED lamps. The base is constructed of heat conducting material and the LED lamps are secured to the base so that heat generated by the lamps is conducted away and dissipated by the base. The base may include a post for supporting a plurality of individually energized arrays of LED lamps. The cover may be optically clear, tinted or provided with facets or a surface texture.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/965,169 filed Aug. 17, 2007. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a warning light and, more particularly, to a warning light utilizing light emitting diodes (LED) to generate warning light signals for use in conjunction with emergency vehicles. 
     BACKGROUND 
     Emergency vehicles are commonly provided with warning lights mounted to the exterior of the vehicle in the form of beacons and light bars. It is also known to provide emergency vehicles with warning lights mounted inside the vehicle to project warning light signals through the windshield or rear window. Further, warning lights have been mounted in the original equipment reflector shells for the front corner, taillight and reverse lights. The standard practice is to drill a hole in the enclosure and mount a halogen bulb or strobe tube in the enclosure. When power is applied to these warning lights, light fills the vehicle reflector and generates warning light signals. 
     Advances in LED brightness allow LEDs to replace halogen bulbs and gaseous discharge strobe tubes to generate warning light signals. 
     SUMMARY 
     The disclosed LED warning lights include a compact lighthead configured for mounting in the original equipment reflector shell of a motor vehicle. Each lighthead includes a base and cover which define an interior space sealed against the elements. The base is constructed of thermally conductive material and includes at least one planar surface to which LED lamps are mounted. The cover is constructed of light transmissive plastic material and configured to mate with complementary structures on the base. The cover is configured to fit through an opening in the reflector shell such that light generated by the LED lamps is emitted into the reflector shell and directed outwardly through the lens of the motor vehicle light. 
     Subsets of the LED lamps are electrically connected in series to form a plurality of LED arrays. Each LED array is provided with its own constant current source. A controller applies timed pulses of electrical current to the arrays to produce warning light signals. The controller is responsive to a pattern select input to select the generated warning light signal from a plurality of patterns stored in memory. A synchronization input to the controller allows the signals generated by multiple lightheads to be coordinated. 
     In one embodiment, each array of LED lamps is arranged on a planar PC board mounted to one side of a shaft in the form of a regular polyhedron. The arrays of LED lamps may be of the same or different colors and may be activated simultaneously or in groups to produce light signals of different colors. An alternative embodiment includes a surface texture on the portion of the cover through which light generated by the LED lamps will pass. The surface texture blends and diffuses light from the LED lamps to illuminate the cover and obscure the internal features of the lighthead during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an embodiment of an LED warning light according to aspects of the disclosure; 
         FIG. 1A  is a top plan view of the post and LED arrays of the LED warning light of  FIG. 1 , showing the patterns of light emission; 
         FIG. 2  is bottom perspective view of the cover shown in  FIG. 1 ; 
         FIG. 3  is a bottom plan view of the cover of  FIG. 2 ; 
         FIG. 4  is a top perspective view of the base shown in  FIG. 1 ; 
         FIG. 5  is a block diagram of a representative warning signal light system including six of the disclosed LED warning lights; 
         FIG. 6  is a perspective view of a second embodiment of an LED warning light according to aspects of the disclosure; 
         FIG. 7  is an exploded view of the LED warning light of  FIG. 6 ; 
         FIG. 8  is a bottom perspective view of a lens for the LED warning light of  FIG. 6 ; 
         FIG. 9  is a top perspective view of a base for the LED warning light of  FIG. 6 ; 
         FIG. 10  is a bottom perspective view of the lens, base, and cable for the LED warning light of  FIG. 6 ; and 
         FIG. 11  is a schematic block diagram of the LED warning light and dedicated power supply of  FIGS. 6-10 . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed LED warning lights are configured for mounting in the reflector shell for front corner, taillight and reverse lights of a motorized vehicle. Such warning lights may be referred to as Hide-A-Way warning lights. A first embodiment of the disclosed LED warning light is designated by the reference numeral  10  and includes a base  5  and mating cover  6  which together define an interior space enclosing a plurality of LED arrays  4 . Each LED array  4  includes one or more LEDs mounted to a thermally conductive PC board. The PC board may be a metal core board or other PC board provided with thermally conductive features. The LED arrays are typically planar. The warning light includes a shaft  7  of thermally conductive material, such as aluminum or die cast metal. 
     In LED warning light  10 , the shaft  7  is square in section and is secured to the base  5  by a screw  8 . Alternatively, the shaft may be molded (cast) integrally with the base  5 . The shaft  7  and base  5  are configured to support the LED arrays  4  and conduct heat away from the LEDs to an area outside the vehicle reflector shell. The base  5  is provided with fins to increase the radiant surface area and improve cooling. Other shaft configurations are possible, with typical sectional shapes in the form of a regular polygon such as a triangle, square, pentagon hexagon, etc. The sides of the disclosed shaft  5  are parallel and the sectional shape of the shaft  5  is constant along its length. Alternative configurations where the sides are not parallel and the sectional shape of the shaft varies along its length may be compatible with the disclosed LED warning lights. 
     The cover  6  is secured to the base by a screw  8  engaging an outer (distal) end of the shaft  7 . The base  5  and cover  6  each include complementary cable openings (wire channels)  19 ,  17 , respectively configured to surround electrical wires extending out of the warning light  10 . The cover  6  and base  5  include mating lip structures  13  (cover),  15  (base) at the periphery of their connection not occupied by the cable openings  17 ,  19 . As shown in  FIG. 3 , the upper inside portion of the cover  6  defines four pairs of ribs  26  arranged to compress the upper ends  27  of the LED arrays  4  against the upper end of the shaft when the cover is installed. The LED arrays  4  are also compressed against the shaft by fasteners  12 . Maintaining face-to-face contact between the LED arrays  4  and the shaft  5  promotes efficient heat transfer. 
     The cover  6  also defines two openings  14 ,  16  communicating with the interior space defined by the cover  6  and base  5 . These openings  14 ,  16  are used to fill the base  5  with encapsulant after the warning light has been assembled. Encapsulant (not shown) is injected into the larger of the two holes  14  while air escapes from the interior space through the smaller of the two holes  16 . The base is filled with encapsulant to a level covering the horizontal PC board  9  and sealing the cable openings from the inside. Encapsulant is filled to the level of the holes  14 ,  16  at the bottom of the cover  6 . The encapsulant seals the cable openings and seals the base  5  to the cover  6  as well as filling the openings  14 ,  16  in the cover  6  to provide a sealed enclosure. 
     In LED warning light  10 , each LED array  4  is provided with its own electrical power. With reference to  FIG. 5 , each of the four LED arrays has its own power wire and is connected to a common ground. The disclosed cable openings (wire channels)  17 ,  19  provide paths for five conductors, one power lead for each array and a common ground. In a typical installation, the five wires leaving an LED warning light will terminate in a plug which will mate with a corresponding plug or socket connected to a jacketed cable having five conductors connected to a power supply  22 . This arrangement permits a controller  20  in the power supply  22  to activate each LED array individually and removes heat generating components such as current sources  24  from within the closed space defined by the cover  6  and base  5 . In some configurations, two of the LED arrays  4  will have LEDs of a first color and the other two of the LED arrays  4  will have LEDs of a second color. For example, two of the arrays  4  may be red and two of the arrays may be blue. The arrays of the same color may be opposite or adjacent each other. A controller  20  may be configured to activate the LED arrays of the first color in an alternating pattern with the LED arrays of the second color to provide a dual color light signal. Alternatively, for certain signals one color may be used, while the other color may be employed for other signals. 
     In the disclosed system, the LED warning lights are driven by one or more remote power supplies  22  configured with current sources  24  for each LED array  4 . Larger current sources could be employed to drive more than one array connected in parallel. Providing each LED array  4  with its own current source and power lead (wire) provides a safeguard against component failure. For example, if an LED or current source fails, only one LED array  4  will be extinguished in the disclosed configuration. The power supply  22  may be configured to sense such failure and provide some indication to those responsible for maintaining the emergency vehicle. The indication may take the form of a visual indicator on the power supply, such as a lit or extinguished LED. Alternatively, the power supply  22  controller  20  may be programmed to alter the warning light signal generated by the LED warning light experiencing the failure or may be programmed to extinguish the LED warning light in question to provide some positive indication of a problem. 
     The power supply will include a controller  20 , typically in the form of a microprocessor programmed to apply power to the LED arrays  4  individually or more typically to all the arrays in a warning light simultaneously to produce light signals. The power supply may have two, four or six outlets. Typical installations will include LED warning lights in the front corners, taillights and/or backup light reflector shells (not shown). The power supply  22  controller  20  is programmed to coordinate the light signals generated by connected LED warning lights  10 . 
     The LED arrays  4  are arranged around the shaft  7  to emit light in a 360° pattern inside the enclosure. In most, if not all, installed orientations of the LED warning light  10 , some of the LED arrays  4  will be oriented to emit light directed at the reflecting surfaces of the enclosure, while other LED arrays  4  will be oriented to emit light directed through the lens of the enclosure. The disclosed LED warning lights  10  fill the reflector to provide a large illuminated surface area and also produce bright illumination directly through the lens of the enclosure. The resulting illumination pattern is very similar to prior art gaseous discharge tubes, with the advantages of LED durability, colored light emission and power efficiency. 
     Each of the disclosed LED arrays  4  include three LUXEON® Rebel LED lamps, each having a typical luminous flux of approximately 100 lm (lumens) at a drive current of approximately 350 mA. In this configuration, each LED warning light produces approximately 1200 lm, or approximately 80 lm per watt of applied power. The selected LEDs may be white LEDs or LEDs of a selected color. The cover may be tinted to filter light generated by white LEDs, for example to an amber/yellow color. Other LED lamps may be compatible with the disclosure. 
     The disclosed LUXEON® Rebel LEDs have a wide angle pattern of light emission with a total included angle θ T  of approximately 160° and a viewing angle θ 1/2  of approximately 70°. The total included angle θ T  is the angle, centered on the optical axis of the LED lamp, within which 90% of the luminous flux produced by the lamp is emitted. The viewing angle θ 1/2  is the angle with respect to the optical axis A O  of the LED lamp at which the luminous intensity of the light pattern is ½ of the peak value. The peak luminous intensity of an LED lamp having a lambertian light pattern is typically at or near the optical axis A O . As shown in  FIG. 1A , the light emission pattern from each LED array  4  overlaps that of an adjacent LED array  4  at B to produce a pattern of light emission surrounding the shaft  7 . 
     The cover  6 , shaft  7  and LED arrays  4  of the disclosed LED warning light  10  are configured to minimize the size of the hole needed for installation. Each of the arrays is approximately 0.28″-0.3″ wide, with each face of the shaft having a corresponding width. The disclosed LED warning light  10  requires a hole 0.75″ in diameter. This configuration also minimizes any disruption of the light pattern generated by the vehicle signal lights used for running lights, turn signal lights and brake light signals. A gasket  11  is positioned between the flared base portion of the LED warning light  10  and the reflector enclosure when the LED warning light is installed to an enclosure to prevent intrusion of moisture and other contaminants. The flared base portion of the LED warning light remains outside the reflector enclosure, while the cover  6 , shaft  7  and LED arrays  4  project into the space defined by the reflector shell. 
     An alternative embodiment of a LED warning light, designated by reference numeral  30 , is illustrated in  FIGS. 6 through 10 . With specific reference to  FIGS. 7 and 9 , alternative LED warning light  30  employs a base  32  and dome-shaped cover  33  which mate to define an interior space. The LED warning light  30  also includes a power supply  60  integrated into the power cable  40 . 
     The base  32  is configured with a circular boss  34  extending upwardly from a flange  36  to a ring-shaped planar top surface  37 . The circular boss  34  is configured with a central aperture  38  to admit a power cable  40 . The base  32  is constructed of thermally conductive material such as die cast metal or thermally conductive plastic or thermally conductive composite material. A PC board  42  having a generally circular configuration is configured for mounting to the top surface  37  of the boss  34  by means of two screws, as shown in  FIG. 7 . 
     Six LED lamps  44  are mounted on the PC board  42  in two arcuate arrays  46  each array including three LED lamps  44 . The three LED lamps  44  in each array  46  are electrically connected in series and receive power from the power cable  40  via traces on the PC board  42 . The PC board  42  may be a standard fiber board material known as FR4 provided with a pattern of copper plated thermal vias (not shown) beneath each LED lamp  44  as is known in the art. Alternatively, the PC board  42  may be a metal-core PC board. The LED lamps  44  are positioned on the PC board  42  and provided with thermal vias to efficiently conduct heat away from the LED lamps  44  to the ring shaped boss  34  and the rest of the base  32 . The LED lamps  44  are LUXEON Rebel LED lamps and may be selected from a variety of available colors or power ratings, depending upon the desired warning light signal and light emission pattern. 
     As best seen in  FIG. 9 , the base  32  includes a flange  36  projecting radially from the bottom of the ring shaped boss  34 . The upper surface of the flange  36  defines a circular groove  48  around the boss  34 . The cover  33  has a dome shape, the upper portion  31  of which is substantially hemispherical as shown in  FIGS. 6-8  and  10 . The cover  33  is configured to surround the boss  34  and provide an enclosed space over the PC board  42  and LED lamps  44 . The bottom of the cover  33  is configured to mate with complimentary features defined by flange  36  of the base  32 . The bottom surface of the cover  33  also includes a circular projection  50  configured to mate with the groove  48  surrounding the boss  34 . The cover also includes diametrically opposed latches  52  which mate with complimentary receptacles  54  defined by the base  32  to secure the cover  33  to the base  32 . 
     During assembly, the PC board  42  with its attached power cable  40  is secured to the top surface  37  of the ring-shaped boss  34  using two screws. A thermally conductive gasket material (not shown) may be interposed between the bottom surface of the PC board  42  and the top surface  37  of the boss  34  as is known in this field. A ring of sealant material (not shown) is extruded into the groove  48  surrounding the boss  34 . The cover  33  is then mated with the base  32 . The circular projection  50  from the bottom of the cover penetrates the groove  48 , contacting the sealant, while the latches  52  on the cover snap into the receptacles  54  defined by the base to retain the cover  33  in mated position while the sealant cures. The cover  33  and sealant prevent moisture penetration between the base  32  and cover  33  around the boss  34 . 
     With reference to  FIG. 9 , the bottom side of the base  32  includes raised fins configured to increase the radiant surface area of the base  32  and enhance cooling. The central portion of the bottom side of the base  32  is bounded by a raised ring  56 . After the PC board  42  and the attached power cable  40  are secured to the base  32 , the base is positioned with the bottom side facing upward and the area bounded by the raised ring  56  is filled with encapsulant material (not shown). Encapsulant fills the opening  38  surrounding the power cable  40  and the holes which receive the PC board mounting screws. Once cured, the encapsulant prevents moisture penetration and provides strain relief for the power cable  40 . The disclosed configurations and procedures provide a lighthead  35  that is sealed against the environment. 
     With reference to  FIG. 11 , the power cable  40  extends from the lighthead  35  to a dedicated power supply  60 . The power cable  40  includes a common ground and a power lead (wire) for each array of LED lamps  46 . The power supply  60  structure includes a housing  62 , PC board  64  and a cover  66 . The PC board  64  includes a controller  61  and two current sources  63 , one current source  63  for each array  46  of three series-connected LED lamps  44  in the light head  35 . The controller  61  is preferably a microcontroller having on board memory and programmed to apply timed power pulses to the arrays  46  of LED lamps  44  to produce warning light signals. An input cable  65  delivers vehicle power, vehicle ground and several input signals to the power supply  60 . The input signals include a synchronization signal SYNC, and a pattern select input. The SYNC signal is an input to the microcontroller  61  allowing the activity of multiple dedicated power supplies  60  to be coordinated to produce synchronized warning light signals. The microcontroller  61  is also responsive to a pattern selection input to select the pattern generated by the lighthead  35  from a plurality of patterns stored in memory as is known in the art. The selected pattern is stored in memory and is generated when vehicle power is applied to the dedicated power supply  60  via an on/off switch. 
     The electrical configuration of the dedicated power supply  60  is similar to that of the remote power supply  22  discussed above in that the plurality of LEDs in each lighthead are divided into series connected arrays  4 ,  46 , each provided with its own current source  24 ,  63 . The current sources  24 ,  63  are responsive to the microcontroller  20 ,  61  to deliver power to the LED arrays  4 ,  46 . 
     The cover  33  may be clear or colored as desired. Light generated by the LED lamps  44  will pass through the upper, hemispherical-shaped portion  31  of the cover  33 . The upper portion  31  of the cover  33  may be optically transparent or may include optical features to spread or distribute light according to the desired radiation pattern. One feature which has proven desirable is to provide a frosted surface texture to the inside surface  39  of the upper portion  31  of the cover  33 . The relevant surface of the mold from which the cover  33  is produced is exposed to a dry grit blast treatment to provide a light surface texture on the corresponding inside surface of the upper portion  32  of the cover  33 . One suitable texture is composed of randomly oriented features having a depth of approximately 0.00004″ or about one micron (μm). Such randomly oriented textures may be produced by a variety of methods including EDM, dry grit (or glass bead) blasting or chemical treatments such as etching. The objective of the disclosed texture is to produce a plastic part which diffuses a small amount of the light emitted by the arrays of LEDs and illuminate the upper portion  31  of the cover  33  during warning light operation. Deeper or more aggressive textures, in excess of approximately 10 μm or about 0.0004″ will typically produce undesirable scattering and internal reflection, which could reduce the overall luminous efficiency of the disclosed LED warning lights  10 ,  30 . 
     In an exemplary embodiment, a mold for the cover  33  is machined from P20 tool steel, the surface of which is finished to an S.P.I. C-2 to C-3 finish to remove any tool marks. The mold is then heat treated to a hardness of 28-32 on the Rockwell Rc scale. The portion of the mold corresponding to the inside surface of the upper portion  31  of the cover  33  is then exposed to a dry grit blast treatment using #220-240 aluminum oxide grit to produce an S.P.I. D-2 finish. One corresponding industry standard is specified by Detroit Mold Engineering with the reference “D-M-E S.P.I. #D-2.” An S.P.I. D-2 finish on the mold produces a part having a “frosted” or matte surface finish. The remaining portions of the mold are polished to an S.P.I. A-2 finish, which results in a smooth, shiny surface on the molded part. 
     Alternatively, the textured surface portions may be provided by electric discharge machining (“EDM”) a corresponding section of the mold with an electric discharge machine. EDM is a process that involves applying a potential difference between an electrode and an electrically conductive workpiece to cause electric discharge therebetween. The impact of the discharge against the workpiece causes the workpiece to be machined. Different roughnesses may be achieved by varying certain operating parameters, such as the electrode material, the magnitude and time-dependence of the electric potential, as well as the electrode-workpiece distance. An EDM machine finish compatible with the textured portion of the cover for the disclosed LED warning lights is “CHARMILLES CH-28.” 
     One measure of surface texture is Roughness Average R a . Roughness average R a , also known as arithmetic average (AA) and centerline average (CLA), is the arithmetic average of the absolute values of the measured profile height deviations taken within the sampling length and measured from the graphical centerline. This type of measurement can be taken by an instrument called a profilometer. The roughness average R a  of a surface texture compatible with the disclosed LED warning lights is between approximately 10 and 40 micro inches or between approximately 0.25 and 1 μm (micron) and more preferably between 20 and 30 micro inches (0.5 μm and 0.75 μm). 
     Light from the LED lamps striking the textured surface of the cover is diffused, causing the upper (hemispherical) portion  31  of the cover  33  to be illuminated. Illuminating the upper (hemispherical) portion  31  of the cover  33  gives the illusion that light is emanating from the upper portion  31  and blends the light from the six LED lamps  44 . When energized, this effect obscures the internal structures of the lighthead  35 . Similar surface treatments may be employed on the cover  6  of the embodiment of the LED warning light designated in this application by reference numeral  10  and illustrated in  FIGS. 1-5 . 
     In a typical vehicle installation, a hole is prepared in the reflector shell of an original equipment vehicle light (not shown). The lighthead  10 ,  35  is secured to the reflector shell with self tapping screws (shown in  FIG. 6 ) with the cover  16 ,  33  protruding into the vehicle light enclosure. A gasket  11 ,  70  is placed between the lighthead  10 ,  35  and the reflector shell to prevent moisture penetration into the reflector shell. 
     It will be appreciated that various of the above-disclosed and other features and functions or alternatives thereof, may be desirably combined into many other different systems, devices or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to by encompassed by the following claims.