Abstract:
An optical waveguide for illuminating the interior of a cup holder in a vehicle is disclosed. The waveguide includes a piece of solid material having a ring portion sized and shaped to be received within a cup holder and configured to release light into the cup holder. An input face receives light from a light source. An input portion extends between the input face and the ring portion. The input portion confines light through internal reflection to direct light from the input face to the ring portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Provisional Application Ser. No. 60/069,118, “HID DRIVEN FOCUS-LESS OPTICS SYSTEM,” filed Dec. 9, 1997 and application Ser. No. 09/009,836, “DISTRIBUTED LIGHTING SYSTEM,” filed Jan. 20, 1998, both of which are incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates to distributed lighting systems. 
     Distributed lighting systems distribute light from one or more light sources in central locations to one or more remote locations. A distributed lighting system promises several advantages over conventional lighting techniques, including low power consumption, extended life, heat reduction where the light is emitted, and increased design flexibility. 
     SUMMARY 
     The invention provides a distributed lighting system (DLS) for use, for example, in an automobile. Issues associated with incorporating a distributed lighting system into an automobile are discussed by Hulse, Lane, and Woodward in “Three Specific Design Issues Associated with Automotive Distributed Lighting Systems: Size, Efficiency and Reliability,” SAE Technical Paper Series, Paper No. 960492, which was presented at the SAE International Congress and Exposition, Detroit, Mich., Feb. 26-29, 1996 and Hulse and Mullican in “Analysis of Waveguide Geometries at Bends and Branches for the Directing of Light,” SAE Technical Paper Series, Paper No. 981189, which are incorporated herein by reference. 
     A practical distributed lighting system for an automobile must address size, efficiency, and reliability issues. To this end, an implementation of the invention employs focus-less optics components, such as collector elements and waveguides. These components are inexpensive to manufacture, since they can be formed from plastic (acrylic, for example) in an injection molding process. In addition, they have high collecting efficiency and are very compact. For example, a collector element may be smaller than one cubic inch (16.4 cubic centimeters). Components that must handle high heat levels (e.g., components are placed in proximity to the light source) may require a ventilation system or may include portions formed from heat resistant materials, such as glass or Pyrex™. 
     The DLS may incorporate different types of optical waveguide structures to distribute light throughout the vehicle, including joints, elements with epoxy coatings, pinched end collector portions, integrated installation snaps, integrated input optics and integrated output lenses. The DLS may also include waveguide structures to provide illumination to portions of the vehicle interior, including cup holders, assist grips, and storage pockets. 
     In one aspect, generally, an optical waveguide for illuminating the interior of a cup holder in a vehicle is formed from a piece of solid material. The solid material has a ring portion that is sized and shaped to be received within a cup holder and that releases light into the cup holder. An input face receives light from a light source. An input portion extends between the input face and the ring portion, confines light through internal reflection, and directs light from the input face to the ring portion. 
     Embodiments may include one or more of the following features. The ring portion may define an inner circumference and may release light around the inner circumference. The ring portion may have a protruding angled portion around the inner circumference that directs light down toward a bottom portion of the cup holder. The upper surface of the angled portion may be stippled. An upper surface of the angled portion may be covered with an opaque material. The ratio of an inner radius of the ring portion to the width of the ring portion may be greater than or equal to 3:1. 
     The ring portion may include a first arm and a second arm that define a gap in the inner circumference. The second arm may have a smaller cross-section and a smaller length than the first arm. The ring portion may have a web portion that extends between the first and second arms. The web portion may release light along its edge. The ring portion may include a tab that extends from the inner circumference between the first and second arms. The tab may have a rectangular cross-section and may curve toward the bottom of the cup holder. The tab may have a chamfered leading edge. 
     The optical waveguide described above may be included in an illuminated cup holder having a bottom surface. A side wall may extend from the bottom surface and define a volume shaped and sized to receive a cup. A rim may be positioned around the upper edge of the side wall. 
     In another aspect, an optical waveguide illuminates the inside of an assist grip in a vehicle. The waveguide is a piece of solid material having an illumination portion with an inner surface and an outer surface. The illumination portion is sized and shaped to be received within a channel along the length of the assist grip and releases light from the inner surface. An input face at one end of the illumination portion receives light from a light source. 
     Embodiments may include one or more of the following features. The inner surface may be stippled. The ratio of the inner radius of a bend to the width of the waveguide may be greater than or equal to 3:1. The waveguide may have snaps extending from the outer surface that hold the illumination portion in place within the channel. A lens positioned adjacent to the light source may focus light from the light source to form a courtesy light. An illuminated assist grip for a vehicle including the waveguide described above also may have a handle portion formed of solid material, a channel formed along the length of the handle and a light source receptacle configured to receive a light source. 
     In another aspect, an optical waveguide for a vehicle door illuminates an area beneath the vehicle. The door has a bottom surface that meets a floor surface of the vehicle when the door is closed. The waveguide includes a door portion positioned inside the door and extending to the bottom surface of the door. A floor portion extends from the floor surface to the underside surface of the vehicle. The door portion and the floor portion meet when the door is closed so that light may pass through the door portion and the floor portion to illuminate the area beneath the vehicle. Embodiments may include a branch that extends from the door portion to an interior surface of the door to illuminate the interior of the vehicle. 
     In another aspect, an illuminated storage pocket for a vehicle has a surface that defines a storage volume and a rim around an edge of the surface. A waveguide formed from a piece of solid material has an illumination portion that has an inner surface and an outer surface. The illumination portion is received within a channel along the rim of the storage pocket and releases light from the inner surface. An input face at one end of the illumination portion receives light from a light source. 
     Embodiments may include one or more of the following features. The inner surface of the waveguide may be stippled. The waveguide may include snaps that extend from the outer surface and hold the illumination portion in place within the channel. 
     In another aspect, an optical waveguide includes a first and a second piece of solid material. The first piece has a transmission portion with a rectangular cross-section. The end of the transmission portion is convex in one dimension. The second piece has a transmission portion with a rectangular cross-section. The end of the transmission portion is concave in one dimension. The end of the first piece and the end of the second piece form an interface between the first and second pieces. 
     Embodiments may include one or more of the following features. The waveguide may include a third piece of solid material having a transmission portion with a rectangular cross-section. The end of the transmission portion may be concave in one dimension. The end of the third piece and the end of the first piece may form an interface between the first and third pieces. A band may hold the first, second and third pieces together. 
     The waveguide may include a third piece of solid material having a transmission portion with a rectangular cross-section. The end of the transmission portion may be convex in one dimension. The end of the third piece and the end of the second piece form an interface between the second and third pieces. A band may hold the first, second and third pieces together. 
     In another aspect, an optical waveguide accepts light from a light source and transmits the light. The waveguide is formed from a piece of solid material having an input face, a transmission portion and an end portion between the input face and the transmission portion. A cross-sectional area of the end portion gradually decreases from the transmission portion to the input portion. 
     Embodiments may include one or more of the following features. The end portion may have planar sides angled from a longitudinal axis of the transmission portion. The angle formed between the sides and the longitudinal axis may be about 5°. The end portion may increase the acceptance angle of the waveguide. A lens portion may be formed on the input face. 
     In another aspect, an optical waveguide has integrated installation elements. The waveguide includes first and second sections. The first section has an input face, an output end and a transmission portion extending from the input face to the output end. A key is positioned on the output end and mates with a socket of the second section. The second section has an input face, an output end and a transmission portion extending from the input face to the output end. A socket is positioned on the output end and mates with the key of the first section. 
     Embodiments may include one or more of the following features. The waveguide may include a snap positioned on the transmission portion of the first or second section. The snap may mate with an installation fitting of a vehicle. The outer surface of the waveguide may be covered with epoxy. 
     In another aspect, an optical waveguide has integrated installation elements. The waveguide includes first and second sections. The first section has an input face, an output end and a transmission portion extending from the input face to the output end. A claw is positioned on the output end and mates with a detent of the second section. The second section has an input face, an output end and a transmission portion extending from the input face to the output end. A detent is positioned near the output end and mates with the claw of the first section. 
     Embodiments may include one or more of the following features. A snap may be positioned on the transmission portion and may mate with an installation fitting of a vehicle. An outer surface of the waveguide may be covered with epoxy. 
     In another aspect, an optical waveguide has an output element for providing illumination in a vehicle. The waveguide includes an input face and a transmission portion extending from the input face. The transmission portion widens at an end to form an output element having a convex lens at the end of the output element. The output element may be formed to leave an air gap between the lens and the end of the transmission portion. 
     Other features and advantages will be apparent from the following detailed description, including the drawings, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a vehicle distributed lighting system with hybrid lighting subsystems. 
     FIG. 2 shows a hybrid headlamp subsystem. 
     FIG. 3 shows a hybrid headlamp subsystem with a movable lens. 
     FIGS. 4A-4D show headlamp beam forming structures. 
     FIG. 5 shows a light source with a diffusion grating. 
     FIGS. 6A-6F show waveguide outputs modulated with electromechanical or liquid crystal light valves. 
     FIG. 7 shows a hybrid tail light subsystem. 
     FIG. 8 shows a compact incandescent cartridge. 
     FIGS. 9A and 9B show a waveguide output bend for a tail light. 
     FIGS. 10A and 10B show a combination security/puddle light. 
     FIGS. 11A-11F show various embodiments of a cup holder illumination component. 
     FIG. 12A is a rear view of a waveguide installed in a handgrip. 
     FIG. 12B is a cross-section view of a waveguide and light source installed in a handgrip. 
     FIG. 12C shows a waveguide with integrated snaps for installation into a handgrip. 
     FIG. 13 is a cross-section view of an optical waveguide. 
     FIGS. 14A and 14B are side and bottom views of a waveguide joint. 
     FIG. 15 is a cross-section view of an epoxy-coated optical waveguide. 
     FIGS. 16A-16C are cross-section views of non-tapered and tapered waveguide inputs. 
     FIGS. 17A and 17B are cross-section views of waveguide sections having integrated installation components and an integrated output structure. 
     FIG. 18 shows a leaky waveguide bend and focusing lens. 
     FIGS. 19A and 19B show cross-section views of optical manifolds. 
    
    
     DESCRIPTION 
     Referring to FIG. 1, a vehicle distributed lighting system (DLS)  100  includes hybrid headlamp subsystems  105 , turn signal subsystems  110  and  140 , and hybrid tail light subsystems  130 . The hybrid headlamp subsystems  105  provide primary forward illumination for the vehicle. The headlamp subsystems  105  are also light sources for other exterior lights, such as front turn signals of the subsystems  110  and side markers  115 , as well as interior lights, such as dashboard lights  120  and dome lights  125 . These other lights are connected to the headlamp subsystems by optical waveguides  135 . Similarly, the tail light subsystems  130  provide light for rear turn signals  140  and a center high mounted stop light (CHMSL)  145 . The subsystems of the DLS are interconnected so that the light source of one subsystem serves as a redundant light source for another subsystem. 
     The DLS incorporates different types of optical waveguide structures to distribute light throughout the vehicle. These include joints, elements with epoxy coatings, pinched end collector portions, integrated installation snaps, integrated input optics and integrated output lenses. The DLS also includes waveguide structures to provide illumination to portions of the vehicle interior, including cup holders, assist grips, and storage pockets. 
     FIG. 2 illustrates a hybrid headlamp subsystem  105 . The subsystem includes a light source  205  that may be implemented using, for example, a high-intensity discharge (HID) lamp. Light produced by the light source  205  is collected by a reflector  210  and directed through a lens  215  to provide the primary forward illumination for the vehicle. The reflector may be implemented as a parabolic or complex reflector. 
     The hybrid headlamp subsystem  105  provides both high beam and low beam illumination. To this end, the subsystem may employ a number of different beam forming techniques, as shown in FIGS. 3-5. For example, FIG. 3 shows a simple Fresnel lens  305  that is moved by an actuator  310  between a high beam position and a low beam position. The movement of the lens  305  shifts the position of the “hot spot” (i.e., the area of most concentrated light) of the headlamp beam in the far field between the appropriate positions for the high and low beams. Other portions of the beam also will shift as the lens moves. In addition to lens, other optical elements, such as wedges, may be used to control the beam pattern. 
     FIGS. 4A-4D show the use of a solid molded plastic form  405  (FIGS. 4A-4C) or a bundle of plastic or glass fibers  410  (FIG. 4D) to generate a desired headlamp beam pattern. Light from light source  205  passes through the form  405  or bundles  410  and then passes through a focusing lens  415 . The shape of the output end  420  of the solid form or bundles, in conjunction with the properties of the focusing lens, determines the beam pattern in the far field. To increase light collection efficiency, the shape of the input end  425  of the solid form may be configured to act as a collector element to receive light from a light source. A reflector  215  may also be used to control the beam pattern, as in FIGS. 2 and 3. FIGS. 4A-4C show dimensions in mm [inches] of a thickness profile that might be used to achieve a desired beam pattern. Similarly, the bundle of fibers can be formed into a desired profile. As with the implementation shown in FIG. 3, the lens  305  may be moved to shift the hot spot of the beam between high beam and low beam positions. 
     FIG. 5 shows the use of a diffraction grating  500  to control the headlamp beam pattern (the diffraction grating may also be used for other lighting functions, such as stop lights and turn signals). The diffraction grating  500  includes essentially transparent material that has a series of ridges  505  on its surface. The width  510  of the ridges is approximately equal to the wavelength of the light produced by the light source  205 . A portion  515  of the light passing through the diffraction grating  500  is reflected back into the light source, with the size of the portion depending upon the exit angle (θ) of the light ray. Most of the light  520  travelling in a direction close to perpendicular (θ=0°) passes through the grating undisturbed. By limiting the exit angle (θ) of the headlamp illumination, the grating  500  may provide, for example, a more focused headlamp beam in the far field. The grating  500  may be used alone or in conjunction with lenses  305 , solid forms  405  or fiber bundles  410  described above to provide a desired headlamp beam pattern. 
     In addition to providing the primary forward illumination, the light source  205  acts as a light source for other parts of the system. As shown in FIG. 2, waveguides  135  having collector elements  220  at their ends are positioned close to the light source  205  to receive light and transmit the light to other locations in the vehicle, such as to provide turn signals, interior lighting, fog lights, and side markers. The waveguides  135  may also carry light to other lighting subsystems to provide redundancy, such as the opposite side headlamp or the tail lights. The number of collector elements  220  may be increased as necessary to supply light for other lighting functions. The collector elements  220  may be glass rods (such as Pyrex) with ends that are polished so as to be faceted or pinched. The pinched ends increase the acceptance angle of the collector element. 
     FIG.  2 . shows a waveguide  225  that carries light from the source to a side marker light  115 . The waveguide  225  may include colored plastic filters  230  to provide a desired output color (e.g., amber) for the side marker  115 . This configuration eliminates the need for an electrical connection and light bulb in the side marker  115 . 
     Another waveguide provides light to the turn signal subsystem  110 . Alternatively, the turn signal subsystem  110  may include an independent light source and may use the input from the headlamp subsystem  105  for redundancy. 
     As shown in FIGS. 6A-6D, some implementations of the turn signal subsystem use an electromechanical shutter  605  (FIGS. 6A and 6B) while others use a liquid crystal light valve (LCLV)  610  (FIGS. 6C and 6D) to modulate the light produced by the turn signal. A plastic colored filter provides amber color for the turn signal. The use of a colored filter eliminates the need for light bulbs enclosed in cadmium-doped glass. 
     The electromechanical modulator  605 , as shown in FIGS. 6A and 6B, includes an opaque shutter  615  that is moved between an ON (FIG. 6A) and OFF (FIG. 6B) position by a solenoid  620 . In the ON position, the shutter  615  is moved away from the illumination path, so that essentially all of the light is transmitted. In the OFF position, the shutter  615  blocks the illumination path so that no light is transmitted. The use of an electromechanical modulator  605  with an amber-colored plastic filter provides a desirable aesthetic effect (i.e., the turn signal appears amber when ON but has no color when OFF). 
     The LCLV illustrated in FIGS. 6C and 6D has no mechanical components. This increases the reliability of the LCLV relating to systems that include mechanical components. The LCLV  610  has two states. In the OFF state (FIG. 6D) the LCLV  610  reflects or scatters most of incident light. In the ON state (FIG. 6C) the LCLV  610  becomes largely transparent (i.e., greater than 80% of incident light passes through the LCLV). The ratio of the light transmitted in the ON state relative to the light transmitted in the OFF state (i.e., the contrast ratio) is approximately 5:1, which meets SAE requirements for a turn signal. A contrast ratio of 5:1 also meets the SAE requirements for stop lights used as turn signals. An infrared reflecting mirror (not shown) may be used to shield the LCLV from infrared energy from the source, thereby increasing the expected life of the LCLV. 
     As shown in FIGS. 6E and 6F, LCLV modulators  610  may be combined with diffraction gratings  500  to improve the contrast ratio and achieve a desired beam pattern. As discussed above, light from the light source (waveguide  135 ) is scattered when the LCLV is OFF (FIG.  6 F). The diffraction grating  500  lessens the amount of forward scattered light that is emitted. Focusing optics, such as lenses  630 , may also be used to provide further beam pattern control. 
     Referring again to FIG. 1, waveguides also may carry light from the headlamp subsystem to other subsystems that have their own light sources, such as the opposite headlamp subsystem (waveguide  137 ) or the corresponding tail light subsystem (waveguide  138 ), to provide light source redundancy. When redundancy is employed and, for example, one of the headlamps fails, light from the operational headlamp will dimly illuminate the failed headlamp. This is safer for the operator of the vehicle than having only one operational headlamp. Redundancy also may be used to reduce the effects of failure of other lighting components. For example, an incandescent PC bulb may be used as a source for trunk lighting and may be connected to provide redundancy to interior reading lights. 
     The tail light subsystems  130  of FIG. 1 operate similarly to the headlamp subsystems. As shown in FIG. 7, a tail light subsystem  130  has a light source  705  that provides primary rear illumination through a lens  710 . The light source  705  may be a HID lamp or another type of lighting source, such as an incandescent lamp, since the lighting requirement (in lumens) generally is less than the requirement for a headlamp. In general, an incandescent source is significantly less expensive than an HID source. 
     A compact incandescent cartridge  800 , such as shown in FIG. 8, may be employed as the light source  705 . The cartridge  800  includes a housing  805  having reflective, heat-dissipating interior surfaces  810 . An incandescent bulb  815  is positioned in the center of the housing  805 . Waveguide collector elements  220  are positioned around the light source. The incandescent cartridge  800  has a compact size, stays cool, and reduces lamp placement error, which increases efficiency. In addition, construction of the waveguide collector elements  220  from injection molding is easy and inexpensive. The cartridge  800  or similar incandescent sources may also be used as light sources elsewhere in the DLS, depending on lighting requirements. In addition, networks of cartridges  800  or incandescent sources may be interconnected to provide redundant light sources for interior or exterior lighting functions in the DLS. 
     Referring again to FIG. 7, waveguide collector elements  220  in the tail light subsystem are positioned close to the source  705  to receive light and transmit the light to other lighting elements, such as the rear turn signals  140 , backup lights  150 , and center high-mounted stop light (CHMSL)  145 . A combination stop/rear turn signal light may be modulated with a LCLV  610 , as discussed above with respect to the forward turn signals. The backup lights  150  and CHMSL  145 , however, are modulated with electromechanical shutters  615 , since they must be completely dark in the OFF mode. 
     The rear turn signals subsystems  140  also may be implemented in the manner shown in FIGS. 9A and 9B. In particular, a waveguide section  900  may be used to provide a desired beam pattern for the rear turn signal. Light from a collector element  220  or an independent light source is received at the input  910  of the waveguide section  900  and is internally reflected by the surfaces of the waveguide as it propagates. The waveguide  900  includes a bend  920  immediately prior to the output  930 . The outer surface of the bend  920  is s-shaped, which changes the distribution of light across the output surface  930  and hence the far field beam pattern of the turn signal. As an example, FIG. 9B shows dimensions in mm [inches] of a waveguide  900  that might be used to provide a desired beam pattern. 
     The DLS also may be used to provide other lighting functions. For example, a waveguide  1000  may be installed in the door  1005 , as shown in FIGS. 10A and 10B, to provide a security/puddle light. The waveguide  1000  runs from a light source, such as the hybrid headlamp subsystem  105  (FIG.  1 ), to the bottom edge  1010  of the door  1005 . A waveguide branch  1012  may be used to implement a interior door light. When the door  1005  is closed, as in FIG. 10A, a door waveguide section  1015  connects to a waveguide  1020  that passes through the floor  1025 . The floor waveguide section  1020  provides a security light that illuminates the area  1030  underneath the vehicle. When the door  1005  is open, as in FIG. 10B, the door waveguide  1015  provides a puddle light that illuminates the ground  1035  between the open door and the vehicle. The bend  1040  in the door waveguide section  1015  may have a bend angle (θ B ) of, for example, 20°. The bend  1040  helps to direct the output of the waveguide  1000  to the desired area. Alternatively, the security/puddle light may be implemented as a hybrid subsystem that has an independent light source. The independent light source may directly provide interior lighting for the vehicle in addition to being connected to the waveguide  1000  as a light source for the security/puddle light. 
     Another waveguide carries light from hybrid headlamp subsystem to the interior of the vehicle to provide, for example, dashboard lighting, dome lights, and reading lights. Waveguides also provide unique, aesthetically pleasing lighting effects for certain interior structures, such as cup holders, map pockets, and assist grips. 
     For example, as shown in FIGS. 11A and 11B, a ring-shaped waveguide element  1100  may be installed under the lip  1105  of a cup holder  1110 . Although the shape of the waveguide  1100  in FIGS. 11A and 11B is circular, any shape may be used depending upon the shape and size of the cup holder  1110 . The efficiency of the waveguide may be improved by selecting a ratio of the inner radius (r) of the waveguide relative to the width (w) of the waveguide. For example, a waveguide with an inner radius to waveguide width ratio (r/w) of 3:1 will lose less light than a ratio of 1:1 or 0.1:1. 
     The waveguide  1100  may have a protruding, angled upper region  1115  to reflect and/or transmit light downward toward the bottom  1120  of the cup holder  1110 . The upper surface  1125  of the angled portion  1115  may be stippled and may be covered with a layer of opaque material to prevent leakage of light in the upward direction. A small incandescent bulb  1130  at the input  1135  of the waveguide is used as a source. Light entering the input  1135  is transmitted to the ring-shaped portion  1136  of the waveguide  1100  via an input portion  1137  that is tangentially connected to the ring-shaped portion  1136 . A colored filter  1145  may be placed between the source  1130  and the input  1135  to achieve a desired illumination color. When illuminated, the interior  1140  of the cup holder  1110  glows faintly so as not to interfere with the driver&#39;s vision. The glowing illumination allows the occupants of the vehicle to discern the location of the cup holder  1110 . Light for the waveguide  1100  also may be provided by a waveguide  135  connected to one of the lighting subassemblies. 
     Another embodiment of the cup holder illumination waveguide  1100  is shown in FIGS. 11C-11D. These “wishbone” shaped waveguides  1100  are configured for cup holders having a gap  1150  to accommodate a mug handle. Light for the waveguide  1100  enters the input  1135  and is split essentially equally to the two arms  1155  of the wishbone. The split in the waveguide  1100  may lead to a dark area in the illumination of the cup holder. Therefore, as shown in FIG. 11C, a web portion  1160  is included between the two arms  1155 . The web portion is thinner than the rest of the waveguide  1100  and provides additional illumination to the portion of the interior  1140  of the cup holder directly beneath the split in the wishbone. 
     Alternatively, as shown in FIG. 11D, a tab  1165  that is thinner than the rest of the waveguide  1100  may extend downward from the split to reflect and/or transmit light toward the bottom of the cup holder. The tab  1165  has a generally rectangular cross-section and curves downward toward the bottom  1120  of the cup holder. As shown in FIG. 11E, the tab  1165  may have a chamfered leading edge  1170 . 
     Yet another embodiment of the cup holder illumination waveguide  1100  is shown in FIG.  11 F. As in the previous embodiment, the waveguide  1100  is configured for cup holders having a gap  1150  to accommodate a mug handle. Light enters the input  1135  and is split unequally between a primary arm  1175  and a secondary arm  1180 . The secondary arm has a smaller cross-section, (i.e., is thinner and narrower than the primary arm  1175 . Since the secondary arm  1180  is shorter than the primary arm  1175 , there is less loss along its length. The smaller cross-section of the secondary arm  1180  allows less light to enter the secondary arm, which balances the light in the two arms  1175  and  1180  provides uniform illumination around the circumference of the cup holder. 
     Similar structures may be used in the interior of a map pocket or, as shown in FIGS. 12A-12C, along the interior surface  1205  of a assist grip  1200 . A length of waveguide  1210  is installed along the inner surface  1205 . The waveguide includes bends  1212  at the ends to conform to the shape of the assist grip. A small incandescent bulb  1215  provides a light source. The bulb may be used in conjunction with a lens (not shown) to provide a courtesy light. Alternatively, the assist grip  1200  may be connected by a waveguide to another light source in the DLS. As shown in FIG. 12C, the waveguide  1210  may be formed with snaps  1220  and  1225  to make installation into the assist grip  1200  easier. 
     Different types of waveguide structures may be used in the DLS to transmit light from the sources to the lighting outputs. A basic waveguide, as shown in FIG. 13, may be formed from optically transparent material such as acrylic or glass. If the waveguide is formed from acrylic or a similar material, it can be manufactured using an injection molding process. The manufacture of waveguide elements using injection molding results in very low manufacturing costs compared to fiber optics. In addition, molded acrylic waveguide elements are more rigid than fiber optics, can be installed by robots, and generally do not require maintenance, waveguide elements can also achieve much smaller bend radii than fiber. 
     As shown in FIG. 13, a light ray  1305  entering the input face  1310  proceeds through the waveguide  1300  until the light ray  1305  reaches an outer surface  1315  of the waveguide  1300 , i.e. an interface between the material of the waveguide  1300  and air. At the outer surface  1315 , light is reflected in accordance with Snell&#39;s law. If the angle of incidence (θ i ) of the light ray  1305  at the outer surface  1315  is less than a threshold referred to as the critical angle (θ c ), then the light ray  1305  is reflected internally, with no light escaping. This phenomenon is known as total internal reflection. The critical angle depends on the index of refraction of the material of which the waveguide is composed relative to that of the material surrounding the waveguide, (e.g., air). For example, if the waveguide were made from acrylic, which has an index of refraction of approximately 1.5, and surrounded by air, the critical angle, θ c , would be: 
     
       
         θ c =arcsin( n   a   /n   b )=arcsin(1/1.5)=41.8  
       
     
     where n a  is the index of refraction of air (1.0) and n b  is the index of refraction of acrylic (1.5). 
     Referring to FIGS. 14A and 14B, a waveguide joint  1400  may be used to distribute light in the DLS. For example, the joint may be used to provide light to a door of the vehicle. The waveguide joint  1400  has a trunk section  1405  with a convex curved end  1410 . Branch sections  1415  having convex curved ends  1420  adjoin the trunk section  1405 . The branch sections may be held in place by a plastic band  1425  surrounding the joint region or by epoxy or snaps. Light input to the trunk section  1405  is essentially split among the branches  1415 . The branches  1415  may be positioned to carry light to different sections of the vehicle. It is also possible to reconfigure the branches  1415  in the event of design changes. Epoxy that has an index of refraction approximately equal to that of the waveguide, i.e., that is index-matched, may be used to hold the branches  1415  in place. The joint  1400  may have only a single branch  1415  that is used to change the direction of the trunk  1405  or to provide a hinged connection. A hinged connection using the joint  1400  may be installed, for example, in a car door. Index-matched fluid may be used to lubricate and reduce discontinuity at the interface between the trunk  1405  and the branch  1415 , which will reduce the loss through the joint  1400 . 
     FIG. 15 shows a waveguide core  1500  encased in a layer of epoxy  1505 . The epoxy coating  1505  may be applied by dipping the waveguide core  1500  (which may be formed, for example, from acrylic) in a reservoir of epoxy and allowing the coating to dry. The epoxy  1505  has a lower index of refraction than the waveguide  1500 , so that most of the light rays  1510  passing through the waveguide core  1500  are internally reflected at the acrylic/epoxy interface  1515 . A portion of the light rays are reflected at the outer epoxy/air interface  1520 . The distribution of light in the waveguide peaks at the center of the waveguide and diminishes toward the edges of the waveguide. Overall, a significant portion of the light is confined within the waveguide core  1500  and only a small portion of the light reaches the outer epoxy/air boundary  1520 . 
     The epoxy coating  1505  offers several advantages compared to an uncoated waveguide. For example, contaminants on the surface of an uncoated waveguide can cause light at the waveguide/air interface to be scattered and transmitted outside of the waveguide instead of being internally reflected, which increases loss in the uncoated waveguide. The epoxy layer  1505  increases the distance between the contaminants and the waveguide core  1500 , which reduces the amount of light that reaches the waveguide/air interface. In addition, plastic coatings can be applied to the outside surfaces  1520  of the epoxy layer, and clamps and other fixtures can be attached to the outside surfaces  1520  with minimal effect on light transmission through the waveguide  1500 . One also could use a waveguide formed from polycarbonate (which has an index of refraction of 1.58) with an outer coating of epoxy (which has an index of refraction of 1.4). Alternatively, one could use a waveguide having a glass core and an outer coating having a lower index of refraction. 
     As shown in FIGS. 16A-C, a waveguide  1600  may have a pinched end that acts as a collector element  1605 . The collector element  1605  increases the acceptance angle (α) of the waveguide  1600  and thereby increases light collection efficiency. The end of the waveguide  1600  may be pinched in two dimensions to form an essentially trapezoidally shaped collector element  1605 . The collector element  1605  may be formed on the end of a waveguide  1600  having a rectangular or round cross-section. 
     For example, FIG. 16A shows a waveguide  1610  without a pinched end. If the critical angle (θ c ) of the waveguide is 45°, the acceptance angle (α) will also be 45°. Light  1615  from a light source  1620  entering the waveguide  1610  at an angle greater than 45° will exit the waveguide  1610  rather than being reflected at the outer surface  1625 . A waveguide  1600  having a pinched end, as shown in FIG. 16B, may have an acceptance angle (α) greater than the critical angle (θ c ). Assuming θ c =45° and the inclined walls  1630  of the waveguide are inclined at an angle of 5° on each side, then the acceptance angle (α) will be 50°. As shown in FIG. 16C, the pinched end of the waveguide  1600  may be formed so that an excess of material at the tip of the waveguide  1600  bulges outward to form a lens  1635  with a desired focal length. The lens  1635  focuses received light, further increasing the acceptance angle of the waveguide  1600 . 
     The waveguides may be formed as a set of standard components that may be easily interconnected and used as building blocks for different applications. For example, FIG. 17A shows waveguides  1700  and  1705  having integrated installation elements, such as snaps  1710  and detents  1715 . Snaps  1710  can be formed during the injection molding of the waveguide  1700  and provide a convenient means for securing the waveguide  1700  within the vehicle. The snaps are sized and angled to minimize light loss through the snap. For example, the snap may form a 60° angle with the waveguide (toward the direction that light is travelling through the waveguide). The vehicle may have brackets to receive the snaps  1710  or a screw may be inserted into a snap  1710  to secure the waveguide to a mounting surface. The detents  1715  enable the waveguide  1700  to be securely connected to another waveguide  1705  having an integrated claw structure  1720 . Each waveguide may be formed with a detent  1715  at one end and a claw structure  1720  at the other. 
     FIG. 17B shows waveguides with integrated connection elements. A waveguide  1740  may have a key  1745  formed at one end. The key  1745  is configured to mate with a socket  1750  of another waveguide  1755 . These connection elements may cause a loss of approximately 4% at the interface, however, the connection elements increase the ease with which waveguide components can be installed. Index-matched epoxy or fluid may be used at the interface to secure the connection and reduce losses. 
     In addition to the installation and connection elements, the waveguide  1700  widens at one end into an output element  1725  having a convex curved surface  1730 . The curved surface  1730  of the output element  1725  essentially acts as a lens to provide a desired light output characteristic. The output element  1725  may form an illumination element for the vehicle, e.g., a courtesy light in the door of a vehicle. A portion of the widened waveguide end may be eliminated, leaving an air gap  1735 , while maintaining desired output characteristics. The air gap  1735  decreases the weight and cost of the waveguide  1700 . 
     Another configuration for an output element is shown in FIG. 18. A waveguide  1800  has a bend  1805  that is configured to allow a portion of the light travelling in the waveguide to escape at the bend  1805 . A lens  1810  may be used to focus the light to form a desired beam pattern. The amount of light released at the bend  1805  can be controlled by determining the inner radius (r) of curvature of the bend  1805  relative to the width (w) of the waveguide  1800 . For example, a bend with a inner bend radius to waveguide width ratio (r/w) of 3:1 will lose less than 5% of the light in the bend. A bend ratio of 1:1 will result in a loss of approximately 30-35%, and a bend ratio of 0.1:1 will result in a loss of approximately 65-70%. Not all of the light released at the bend enters the lens, however the amount of light entering the lens will be proportional to the amount of light released at the bend. 
     An optical manifold  1900 , as shown in FIGS. 19A and 19B, is another useful building block for a DLS. Light enters the optical manifold  1900  through one or more inputs  1905  and is split to one or more of the output arms  1910 . Alternatively, light may enter through one or more output arms  1910  and exit through the inputs  1905 . The output arms  1910  may branch off at multiple points from the optical manifold in multiple directions to direct light to other subsystems of the DLS in various locations within the vehicle. The size of the output arms  1910  and their locations determines the proportion of the light input to the manifold that is split to each arm. 
     As shown in FIG. 19B, the optical manifold  1900  may include integrated output elements  1915 . The output element  1915  may be lens-like structures that provide lighting functions within the vehicle, such as a reading lights or dashboard lights. The manifold  1900  may have multiple input  1905  and output arms  1910  and a portion  1920  where light from the various inputs is combined. Each input and output may use colored filters to achieve desired lighting effects. 
     Other embodiments are within the scope of the following claims.