LED headlamp system

A solid-state light source (10) comprising a plurality of LED units (12) arrayed to emit light generally about an axis (14). Each of the LED units (12) can comprise a number of LEDs, for example, up to five. They may all emit in a single color or multiple colors can be combined for a specific effect. A light transmissive light guide (16) is associated with the LED units (12) and has a plurality of input widows (18). Each LED unit (12) faces a respective input window (18) and each window (18) transversely intercepts the axis (14) and receives light from the LED units (12). The input windows (18) lead to a common output window (20) that is axially aligned with the input windows (18). The light guide (16) has smooth sidewalls (22) that extend between the input windows (18) and the output window (20).

TECHNICAL FIELD

This invention relates to light sources and more particularly to solid-state light sources. Still more particularly it relates to solid-state light sources that can be employed in a headlamp to mimic the light distribution pattern of an incandescent light. Still more particularly, it relates to solid-state light sources useable as automotive headlamp lighting.

BACKGROUND ART

LEDs are now being used in a variety of lighting application, both for efficiency and durability. One of the most difficult lighting applications is automotive head lighting, and there is a drive to use LEDs in headlamps because of their long life and ruggedness. Good luminance is required, but LED are significantly less luminous than tungsten halogen filaments or arc discharges; therefore, a plurality of LEDs must be used to generate the total number of lumens required. This may be achieved by ganging a plurality of LEDs together, but dispersed light sources are difficult to optically integrate, and forward automotive lighting requires excellent beam direction. There is then a need for an LED headlamp system with sufficient lumens and good beam structure. It is possible to achieve the headlight function by dispersing LEDs over a great area. This helps resolve the problem of excessive heating, but it exaggerates the beam building and optical problems by requiring beam alignments from differing directions. It also forces the housing and support structures to be large, cumbersome and expensive. There is then a need for an optically compact LED head lighting system.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the invention to obviate the disadvantages of the prior art.

It is another object of the invention to enhance LED headlamps.

These objects are accomplished, in one aspect of the invention, by the provision of a solid-state light source that comprises a plurality of LED units arrayed to emit light generally about an axis. A light transmissive light guide has a plurality of input widows with each LED unit facing a respective input window. Each window transversely intercepts the axis and receives light from the LED units. A common output window is axially aligned with the input windows. The light guide has smooth sidewalls extending between the input windows and the output window and a lens is axially aligned with the output window and has a focal point positioned relative to the output window to refract light received from the output window into a preferred beam pattern directed to a field to be illuminated. An electrical connector provides power from an external source to energize the LED units, and a housing retains the LED units, light guide, lens and electrical connector in proper relation.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings with greater particularity, there is shown inFIG. 1a solid-state light source10comprising a plurality of LED units12arrayed to emit light generally about an axis14. Each of the LED units12can comprise a number of LEDs, for example, up to five. They may all emit in a single color or multiple colors can be combined for a specific effect. A light transmissive light guide16is associated with the LED units12and has a plurality of input widows18. Each LED unit12faces a respective input window18and each window18transversely intercepts the axis14and receives light from the LED units12. The input windows18lead to a common output window20that is axially aligned with the input windows18. The light guide16has smooth sidewalls22that extend between the input windows18and the output window20to enhance total internal reflection in the light guide16.

A lens24is axially aligned with the output window20and has a focal point positioned relative to the output window to refract light received from the output window20into a preferred beam pattern directed to a field to be illuminated.

An electrical connector26provides power from an external source to energize the LED units.

A housing28, which can also function as a heatsink, retains the LED units12, the light guide16, the lens24and electrical connector26in proper relation. To increase the heatsinking function, a plurality of heat-radiating fins29can be provided on the housing28.

In a preferred embodiment of the invention, the output window20has an area less than 40 square millimeters.

A vehicle lamp system30, shown diagrammatically inFIG. 5, can comprise a plurality of solid-state light sources10, with different sources being formed to provide different light outputs, for example, on light source10can provide a high beam and one can provide a low beam.

Further, the light sources can be configured to provide beam spread functions, hot spot beam functions, etc.

The LED units12can be contained in ceramic fixtures mounted directly on a printed circuit board. The units12are preferably arranged in one or two lines, as shown inFIGS. 2 and 3.

The light guide16is formed from a light transmissive material. Glass or plastic, such as polycarbonate may be used. The preferred material is moldable so as to inexpensively take the preferred optical form. The light guide has one or more input widows18transversely intercepting the beam axis14to face the one or more LED units12and receive light from the one or more LEDs. In the preferred embodiment, there is one light guide input window18for each LED unit12. If desired, two or more LED units12could be directed into a particular input window18. The preferred individual input windows18then span a respective one of the LED unit's output region to capture a substantial part of the emitted light. If there are five LED units12, for example, in the beam function array, then there are five separate input windows18, each one closely positioned to span the emission region of the corresponding LED unit. Alternatively, the input window could span all of the LEDs in an array. For example, if five LED units make up the horizontal band of the high beam spread function, the one input window, would have a horizontal width slightly greater than five times the LED unit width plus the gap between the adjacent LED units to thereby span the output regions of the five LED units.

The light guide16includes a common output window20axially aligned with the input window or windows18, and spanning the plurality of input windows. The common output window20, in the preferred embodiment, has a greater area than the input window areas, but is still preferably sized to mimic a filament. In general it is desirable to have as small an output window as possible, ultimately creating an ideal optical point source. Unfortunately, a small output window cuts off the amount of light passed, and transmission has to be balanced against optical size. The light guide16has smooth sidewalls extending between the input window and the output window to enable total internal reflection.

Supporting legs32position the light guide16in position on the housing28, for example, by flanges34that can receive bolts36. The light guide16may formed to bridge the LEDs12, then be anchored by the legs32to the housing28so as to securely and accurately fix the input windows18adjacent the LEDs12. In the preferred embodiment, the light guide with input windows, output window and the support (legs32) is a unitary body molded from a light transmissive material that is anchored to the substrate supporting the array of LEDs, thereby accurately fixing the input windows in a face to face relation with the respective LEDs.

Overall, this gives the preferred light guide the. form of a plurality of tapered portions with their respective narrow input windows18facing their respective light supplying LED units12, while the broader output ends are merged together as a single output window20. The preferred sidewall angle(s) from the respective input windows to the common output window correspond to the beam angle for that particular beam function. There may then be light guides with a high and low beam hot spot angles, high and low beam spread angles. Similarly there may be light guides for bending beam functions; that is to say, dynamic turning lighting or advance forward lighting system lighting, and also fog lamp, signaling, daylight running, marker or other functions where the spread (height and width angles) of the desired beam are initiated in the light guide structure. It is also desirable to include other beam features that smooth, fill in or style the look of the headlamp. All of these differing functions can be accommodated in the plurality of light source assemblies.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.