with reference to fig2 and 3 , an led - based light source 40 is employed in a traffic light ball 10 , such as shown in fig1 . the led - based light source 40 replaces only the light bulb 12 of fig1 . the cover 28 and the existing optics such as the reflector 22 and the lens 24 are physically and functionally retained as seen in fig2 . the source 40 includes a threaded electrical connector 42 that mechanically and electrically conforms with the connector 16 of the light bulb 12 , so that the source 40 is installed into the threaded socket 18 similarly to the light bulb 12 , that is , by screwing the source 40 into the socket 18 to effect electrical connection and mechanical support . the led - based lamp 40 also includes electrical power conditioning electronics 44 . as is known to those skilled in the art , incandescent traffic lights are typically powered by a . c . electrical voltage sources in the range of about 80 - 135 volts ( for the nominally 120v a . c . north american standard ) or about 185 - 275 volts ( for the nominally 220v european standard ), and typically draw hundreds of milliamperes of current . the led source 40 , in a suitable embodiment , includes a plurality of leds 46 each operating at a few volts d . c . and drawing a few tens of milliamperes . hence , the power conditioning electronics 44 receive electrical power from the threaded electrical connector 42 and condition the electrical power to operate the leds 46 . in one suitable embodiment , the conditioning electronics 44 include a switching power supply ( not shown ) for converting the a . c . line voltage to a d . c . rectified current adapted for powering the leds . preferably , the switching power supply has a high power factor and low current harmonic distortion . switching power supplies typically have very low power loss and advantageously include the capability of controlling the output current to optimally drive the leds 46 . of course , if the leds 46 adequately perform using the power supplied by the threaded socket 18 , the conditioning electronics 44 are optionally omitted . in another contemplated embodiment the conditioning electronics 44 are physically integrated into the threaded electrical connector 42 to minimize the size of the source 40 . in one suitable embodiment , the leds 46 are white light - emitting leds such as white light - emitting phosphor - coated ultraviolet gan leds known to the art . the use of white light - emitting leds makes the led - based lamp 40 a spectrally close retro - fit for the light bulb 12 which typically emits white light . a retro - fit led - based lamp 40 that employs white light - emitting leds can be used for retro - fitting any of the red , yellow , or green balls of the conventional three - color traffic light . although employing white - light leds enhances retro - fit interchangeability , the use of a white light - emitting source in the traffic light ball 10 is optically inefficient to the extent that the tinted filter or lens 24 blocks and removes light outside of a selected narrow pass - band . for this reason , in another suitable embodiment the leds 46 include colored leds which produce light predominantly in the selected filter pass - band . thus , red leds are advantageously employed for retro - fitting a red traffic light ball , yellow leds are advantageously employed for retro - fitting a yellow traffic light ball , and green leds are advantageously employed for retro - fitting a green traffic light ball . since the selected color conforms with the pass - band of the tinted filter or lens 24 , the spectral filtering element need not be removed during the retro - fitting . because the colored leds produce light substantially within the pass - band of the tinted filter or lens 24 , the retrofitted source operates with higher optical output efficiency even with the tinted filter or lens 24 in place . suitable colored leds include for example algainp - based leds and gan - based leds ( with or without phosphor coatings ) known to the art . of course , other leds with suitable optical characteristics are also optionally used . because colored leds inherently define the signal ball light color , if colored leds are used the tinted filter , if present , is optionally removed . similarly , if the lens 24 is tinted , it is optionally replaced by a clear lens . an advantage of performing this removal or replacement is that phantom light reflected by the signal ball without tinted filter is spectrally unaltered . because the phantom light is not filtered , the reflected light does not appear as spectrally pure red , green , or yellow light and is therefore less likely to confuse roadway users errantly thinking that the traffic light is activated . another advantage of removing the filtering element is that optical power losses that potentially result from any spectral mismatch between the colored leds and the filter pass - band or from non - unity light transmission by the filtering element within the pass band are avoided . the led lamp 40 advantageously includes heat sinking to control heat generated by the led lamp 40 . in a suitable embodiment , a heat sink is provided in the form of heat - radiating fins 48 arranged around the power conditioning electronics module 44 . in another suitable embodiment , a heat sinking path ( not shown ) is arranged to conduct heat from the leds 46 and the electronics module 44 into the threaded electrical connector 42 and the threaded socket 18 . in yet another suitable embodiment a large heat - capacity element ( not shown ) is arranged within the led lamp 40 in thermal contact with the heat generating elements to increase the overall heat capacity of the led lamp 40 and thus reduce the lamp &# 39 ; s operating temperature . the leds 46 produce light 60 in a generally forward direction corresponding to the direction of the outwardly directed light beam the traffic signal ball 10 should produce . however , the forwardly directed light 60 can be too narrowly collimated to meet the practical and regulatory requirements for a traffic signal light beam . an optical element 62 is therefore advantageously arranged to disperse or redirect the forwardly directed light 60 in conformance with the traffic signal light optics , i . e . the reflector 22 and the lens 24 . light dispersed by the optical element 62 is received by the optical system exemplarily comprising the reflector 22 and the lens 24 and is substantially collimated by the optical system to produce an outwardly directed light beam with a selected beam spread that meets the practical and regulatory requirements . in a suitable embodiment , the optical element 62 is a dispersing reflector formed of a light - transmissive encapsulant 66 surrounding the leds 46 and having a surface 68 defining the reflector shape , and a reflective material 70 arranged on the surface 68 to enhance the reflectivity . the reflective material 70 is optionally a metallic coating of high reflectivity . for colored led light , a multiple - layer dielectric stack mirror is optionally used . such dielectric stacks can be tuned to have very high reflectivity over a selected spectral range coinciding with the colored led light output . in another contemplated embodiment , the optical element 62 employs total internal reflection at the surface 68 to redirect the light . the optical element 62 reflects the forwardly directed light 60 to produce reflected light 72 generally directed toward the reflector 22 of the traffic light ball 10 . for replacing the light bulb 12 , the reflected light distribution preferably approximates the point source or line source corresponding to the filament 14 . in the exemplary embodiment of fig2 and 3 , the reflector shape - defining surface 68 is a depression in the encapsulant 66 . the reflecting material 70 is a high - reflectivity filling material disposed in the depression . in the retro - fit configuration of fig2 the surface 68 is physically positioned at approximately the same location as the filament 14 of the light bulb 12 . in a typical incandescent traffic signal ball 10 arrangement , the filament 14 is positioned at a focal point of the reflector 22 . the reflector 22 collects light from the filament 14 disposed in the focal region and forms the light into an outwardly directed light beam . thus , arranging the optical element 62 in the reflector focal region so as to disperse the led light 60 away from the focal region suitably adapts the led light 60 for collimation by the reflector 22 . in one contemplated embodiment , the reflective material 70 includes a partially reflective , partially transmissive element that in addition to producing reflected light 72 also passes a fraction of the forwardly directed light 60 as transmitted light 74 . the ratio of reflected light 72 to transmitted light 74 is selected to closely model the light output of the filament 14 of fig1 which as a point or line light source typically generates light directed toward the reflector 22 as well as outwardly directed light which does not impinge on the reflector 22 . by including partial light transmission 74 , a more accurate retro - fit of the light bulb 12 is obtained , independent of the traffic light or other optical system with which it is to be used . however , in another contemplated embodiment the reflective material 70 is fully reflective so that only the reflected light 72 is produced . in yet another suitable embodiment of the optical system 62 , the reflective surface 68 is replaced by a lensing system ( not shown ) that couples the generally forwardly directed light 60 with the reflector 22 . in still yet another suitable embodiment , a transparent light scattering material ( not shown ) is arranged at the reflector focus to scatter and disperse light into the reflector 22 . although the light source 40 of fig2 and 3 is described with reference to a retro - fit of an incandescent traffic light ball 10 , it is not limited thereto . the led - based traffic light ball is optionally specifically designed for operation with the led light source 40 , rather than for operation with an incandescent light bulb . in this case the traffic light ball optics such as the reflector and the lens are preferably configured to optimally capture and re - direct light generated by the light source 40 to form a light beam having a selected beam spread and other characteristics . the light source 40 is also suitable for use in other lighting systems employing incandescent or other types of light generation . those skilled in the art will further appreciate that a custom reflector and lens are optionally physically integrated with the led light source 40 to form a unitary threadedly connectable light source with integral optics that produces a selected light beam , such as a spot beam or a flood beam . such a unitary threadedly connectable led - based light source can serve for example as an led - based replacement for par - type incandescent or halogen light bulbs . with continuing reference to fig1 - 3 and with further reference to fig4 a suitable method 100 for retro - fitting a traffic light ball 10 with the led light source 40 is described . in a step 102 the traffic signal lamp cover 28 is opened . in a step 104 the threaded light bulb 12 is removed from the threaded socket 18 . in a step 106 the threaded led light source 40 is connected to the threaded socket 18 . in a step 108 the traffic signal lamp cover 28 is closed . unlike other led retro - fitting methods , the method 100 preferably does not involve removal or replacement of any component of the traffic light ball 10 except the light bulb 12 . in the event of a future failure of the led - based lamp 40 , it can be replaced by another led - based lamp . alternatively , the lamp can be re - fitted with an incandescent light bulb , by simply removing the led light source 40 and re - installing a light bulb into the threaded socket 18 . even in the case where the leds 46 are colored leds corresponding to the selected traffic light ball ( red , green , or yellow ), the tinted filter or lens 24 is optionally not replaced , since the colored led light output corresponds to the filter pass - band . however , if colored leds are used the tinted filter can be removed , or the tinted lens 24 can be replaced by an optically clear lens ( steps not shown ). furthermore , the method 100 is optionally performed with the traffic light ball 10 fully energized , since the threaded socket 18 is designed for safe electrical connection while electrically hot . of course , to fail - safe the retro - fitting , the traffic light is optionally de - energized prior to the retro - fitting . since any geometrical filters of the traffic light ball 10 are retained , the same type of led - based lamp 40 is preferably used regardless of the spatial geometry of the traffic light ball 10 . for example , the led lamp 40 of fig2 and 3 is suitable for retro - fitting into a round signal ball , a left - turn arrow signal ball , an “ x ” signal ball , a pedestrian “ walk ” or “ don &# 39 ; t walk ” signal ball , or the like , because the geometrical filter defining the arrow , “ x ”, etc ., is operatively retained . maintenance crews and traffic departments can maintain a single type of led - based lamp in stock which is suitable for installation into traffic light balls of various colors and geometries . if colored leds ( rather than white light - emitting leds ) are used in the led lamp 40 , separate stocks of the red , yellow , and green led - based lamps are preferably maintained . the invention has been described with reference to the preferred embodiments . obviously , modifications and alterations will occur to others upon reading and understanding the preceding detailed description . it is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof .