GB2323917A

GB2323917A - Vehicle lighting system

Info

Publication number: GB2323917A
Application number: GB9806757A
Authority: GB
Inventors: Jeffrey Thomas Remillard; David Allen O'neil; Timothy Fohl; Michael Anthony Marinelli
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 1997-04-01
Filing date: 1998-03-31
Publication date: 1998-10-07
Anticipated expiration: 2018-03-31
Also published as: DE19812793A1; GB9806757D0; GB2323917B; DE19812793B4

Abstract

A lighting system for an automotive vehicle includes a remote laser light source (12 fig 1) coupled with a light transmitting fibre optic light guide bundle (14 fig 1) for illuminating a uniform thickness thin sheet optical element (16 fig 2) having a plurality of micro-optical wedges 26 formed thereon and holographic extractors 30 disposed along a side surface 24 of the optical element (16) for receiving and redirecting light of a uniform intensity distribution to predetermined regions of the micro-optical wedges 26.

Description

2323917 - 1 VEHICLE LIGHTING SYSTEM The present invention relates to a

vehicle lighting system.

Conventional light transmission systems used for vehicle head lights or tail lights typically use a bulb and reflector system. In a bulb and reflector system, the filament of the bulb is placed at or near a focal point of a parabolic reflector. The light emitted by the bulb filament is collected by the reflector and reflected outward to form a light beam. A lens is used to shape the light beam into a specified pattern to satisfy vehicle lighting specifications. In a typical automotive application, a conventional bulb and reflector system collects and reflects only thirty percent of the light emitted from the bulb filament into the useful lighting area.

Bulb and reflector systems have several disadvantages, including disadvantages related to aerodynamics and aesthetic styling. For example, the depth of the reflector along its focal axis and the height of the reflector in directions perpendicular to the focal axis greatly limit attempts at streamlining vehicle contours. Additionally, thermal energy given off by the bulb during operation must be considered. The size of the reflector as well as the material used in its construction vary depending upon the amount of thermal energy generated by the bulb filament. Decreasing the size of the reflector requires use of materials with high thermal resistivity for the reflector.

One approach to develop an automotive lighting system for use with newer streamlined body designs is proposed in U.S. Patent No. 5,434,754, assigned to the assignee of the present invention, which discloses the combination of a fibre optic light guide which transmits light from a remote light source, to a parabolic reflector, through a light manifold, and to an optical element. One problem with such an approach is the necessity for a manifold. A manifold is required to expand the incoming light for distribution across the optical element surface. This results in a substantial portion of unlit area required for the manifold and hence a larger footprint of the overall lamp. This creates vehicle lighting design inflexibility. Another problem is the necessity for collimating optics such as parabolic reflectors. Collimating optics are required to direct collimated light to predetermined regions of the manifold and optical element. These optics add to design and manufacturing costs. A further problem with such an approach is that the kicker gradually decreases in thickness. The kicker has a series of steps formed in the back surface. This necessitates a gradual taper in thickness from the first to the final steps in the series. This variance in thickness results in a portion of the lamp which is thin, weak and susceptible to breakage.

A problem with thin sheet optical elements is the difficulty in attaining a uniform light intensity distribution for the front surface. For example, if a flat panel is illuminated with a plurality of LED's disposed along an edge, the illuminated front surface will have a light "'stripe" appearance. This is an undesirable result for vehicle styling requirements.

Therefore, it would be desirable to provide a laser illuminated, uniform thickness, thin sheet optic lighting system for a vehicle which accommodates manufacturing and thermal considerations as well as the space limitations dictated by vehicular aerodynamic and styling requirements.

According to the present invention, there is provided a lighting system for use in an automotive vehicle, comprising at least one light source for generating light; a uniform thickness thin sheet optical element having a first surface, a second surface with a plurality of micro-optical wedges formed thereon for receiving and reflecting light through the first surface, and a perimeter side surface with a side surface length generally normal to the first surface; and at least one holographic extractor disposed along the perimeter side surface having a length substantially equivalent to the side surface length, for receiving and transmitting light through the perimeter side surface toward the micro-optical wedges, the light having a predetermined luminous intensity distribution after passing through the first surface.

In a preferred embodiment of the present invention, a vehicle lighting system further includes a remote light source coupled with a light transmitting fibre optic light guide bundle which in combination illuminates the uniform thickness thin sheet optical element.

The present invention provides a uniform thickness, thin sheet optical element lamp with a reduced overall footprint.

Further, there is provided a holographic extractor for expanding light. This element eliminates the need for a manifold thereby reducing the overall footprint of the tail lamp which allows for greater vehicle design flexibility. The holographic extractor also collimates and directs light thus eliminating the need for beam forming optics, such as parabolic reflectors, which reduces design and manufacturing cost. Further, the holographic extractor is designed to provide a predetermined uniform light intensity distribution which provides a uniformly lit optical element.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of an automotive vehicle having a vehicle lighting system according to a preferred embodiment of the present invention; Figure 2 is a top view of a uniform thickness thin sheet optical element according to the present invention; Figure 3 is a side view of a uniform thickness thin sheet optical element according to the present invention; Figure 4 is a side view of an alternative embodiment of a uniform thickness thin sheet optical element according to the present invention; and Figure 5 is a side view of a holographic extractor producing a uniform intensity light distribution.

Turning now to the drawings, and in particular to Figures 1 and 2 thereof, an automotive vehicle 10 is shown having a vehicle lighting system using, in combination, a remote laser light source 12, a fibre optic light guide bundle 14, and a unifo=n thickness thin sheet optical element 16. The uniform thickness thin sheet optical element 16 of the present invention is configured as a tail lamp 18, but may also be a head lamp or used for other vehicle lighting applications as those skilled in the vehicle lighting arts will recognise. Therefore, the configuration of Figure 1 is meant only to be illustrative and not limiting.

For illumination of the tail lamp 18, the laser light source 12 preferably emits red coherent light. The remote laser light source 12 is positioned in the automotive vehicle 10 with consideration given to vehicle design requirements and manufacturing ease relative to the particular lighting objectives. A possible location for the remote laser light source 12 is in the engine compartment (not shown). A single diode laser is preferably used although other types of lasers as well as other types of remote light sources may be used without departing from the scope of the present invention. Alternatively, multiple laser sources or high intensity LED's may be positioned directly adjacent the uniform thickness thin sheet optical element 16 depending on the particular vehicle design requirements.

Preferably a fibre optic light guide bundle 14 is utilised to transmit light from the remote laser light source 12, as shown in Figure 1. In the present embodiment each fibre optic light guide bundle 14 has two individual fibre optic light guides. Each of the two light guides has a first end 34 and a second end 36. Because of the high brightness (candela per unit area) of the laser, small diameter (0.1-1.Omm) light guides are preferably used to transmit the light.

The uniform thickness thin sheet optical element 16, as depicted in Figure 2, is generally planar, rectangular and ranging in thickness from 1Ogm-6mm. A variety of curved profiles may also be used for the optical element 16 without departing from the scope of the present invention. The optical element 16 is preferably made from a transparent, solid piece of plastic such as polycarbonate and utilises the principle of total internal reflection (TIR) to reflect light. TIR is explained in more detail below. Other transparent materials such as acrylics may also be used.

An advantage of using a uniform thickness cross-section is that the optical element 16 is stronger and more robust than the tapered crosssection of previous designs. This allows designers more flexibility with the shape and size of the footprint of the optical element 16. Additionally, the robust optical element 16 may be used for a vehicle outer lens. This is particularly advantageous because the reduction in lamp componentry lowers cost and weight and simplifies assembly. If the optical element 16 were used for an outer lens, a clear coating such as Teflon would preferably be applied to the front surface 20. This coating has a predetermined index of refraction to prevent dirt or water on the outer lens from causing light to escape from the optical element 16.

As depicted in Figures 3 and 4, the optical element 16 has a front surface 20, a back surface 22, and a perimeter side surface 24. The front surface 20 is generally parallel to the back surface 22. The perimeter side surface 24 is generally normal to both the front and back surfaces, 20 and 24 respectively and has a predetermined side surface length 23. Disposed upon the back surface 22 are a plurality of micro-optical wedges 28. Micro-optical wedges 26 may also be disposed on the front surface 20. Each micro-optical wedge has a reflective surface 28 having a predetermined angle relative to the front surface 20. The predetermined angle may vary with each micro-optical wedge 26 depending on the beam pattern desired. The micro-optical wedges 26 of the optical element 16 are preferably divided into four optical zones: 38, 40, 42, and 44 as shown in Figure 2.

As shown in Figures 2 and 3, preferably two holographic extractors 30, each having an extractor length 32 and a light receiving end 25, are disposed along the perimeter side surface 24 in opposing fashion. The extractor length 32 is substantially equivalent to the side surface length 23. The substantially equivalent lengths facilitate the desired uniformly lit appearance of the front surface 20. 10 The number of holographic extractors 30 is preferably equivalent to the number of light sources since the light from the light sources must be processed by the holographic extractors 30 before entering the optical element 16. In a preferred embodiment, two fibre optic light guides provide is the required light. The holographic extractors 30, as disclosed for example in U.S. Pat. No. 5,515,184 and herein incorporated by reference, may be formed integrally with the optical element 16 or may be separately attached to the perimeter side surface 24. As shown in Figure 5, the holographic extractors 30 are designed to precisely control the amount of light each zone receives as well as provide a uniform intensity light distribution 31 across the optical element 16. Light is directed by the holographic extractor 30 to a specific zone of the micro-optical wedges 26 to provide the desired beam pattern.

There are many advantages to utilising the holographic extractors 30. One advantage is that the holographic extractors 30 function to expand incoming light. The manifold portion of previous designs may now be eliminated. This promotes greater design flexibility. Another advantage is that the holographic extractors 30 also function to collimate and direct light. The parabolic reflectors of previous designs are now unnecessary. This reduces design and manufacturing cost. A further advantage is that the holographic extractors 30 function to provide a uniform intensity light distribution 31 as seen from a given perspective.

7 As shown in Figures 3 and 4, an additional beam forming device 33 may be employed depending on the beam pattern desired. Examples of such beam forming devices 33 are holographic diffusers, pillow optics, diffractive optics, or others known in the art. These optical elements may be formed integral with the front surface 20 of the uniform thickness thin sheet optical element 16.

The first end 34 of each fibre optic light guide of the fibre optic light guide bundle 14 is connected to the remote laser light source 12 via a light coupler (not shown) such as those known in the art. The second end 36 of each fibre optic light guide of the fibre optic light guide bundle 14 is optically coupled to the light receiving end 25 of a corresponding holographic extractor 30.

is In use, light is emitted from the remote laser light source 12, received by the fibre optic light guide bundle 14 via light couplers, transmitted through the fibre optic light guide bundle 14 via TIR, and emitted at the second ends 36 incident upon the light receiving end 25 of the holographic extractors 30. In a preferred embodiment, the holographic extractors 30 divide the light into an angular distribution such that the light is directed through the perimeter side surface 24 toward the front surface 20. The light reflects at least once off of the front surface 20 and is directed to a specific zone of the plurality of micro- optical wedges 26 of the back surface 22. The light striking the micro-optical wedges 26 is redirected via TIR out of the uniform thickness thin sheet optical element 16 through the front surface 20.

Total internal reflection (TIR) of light occurs when an incident angle 0 of light upon a surface exceeds a critical angle 0,, given by the equation 0, = sin-' (nl/n2) wherein nj is the index of refraction of air and n2 is the index of refraction of plastic. The plastic-air interface can be metalised if necessary to prevent the light rays from reflecting out of the plastic medium.

In an alternative embodiment, as depicted in Figure 4, the light from the holographic extractors 30 passes through the perimeter side surface 24 and is transmitted directly to a predetermined micro-optical wedge 26 zone 38, 40, 42, or 44.

9

Claims

A lighting system for use in an automotive vehicle, comprising: at least one light source for generating light; a uniform thickness thin sheet optical element having a first surface, a second surface with a plurality of microoptical wedges formed thereon for receiving and reflecting light through the first surface, and a perimeter side surface with a side surface length generally normal to the first surface; and at least one holographic extractor disposed along the perimeter side surface having a length substantially equivalent to the side surface length, for receiving and transmitting light through the perimeter side surface toward the micro-optical wedges, the light having a predetermined luminous intensity distribution after passing through the first surface.
2. A vehicle lighting system according to claim 1, wherein the received and transmitted light passing through the perimeter side surface reflects off the first surface before being directed to the micro-optical wedges.
3. A vehicle lighting system according to claim 1, wherein said uniform thickness thin sheet optical element is comprised of a polymeric transparent optical material.
4. A vehicle lighting system according to claim 1, wherein said uniform thickness thin sheet optical element has a thickness between 1Ogm-6mm.
5. A vehicle lighting system according to claim 1, wherein said at least one light source is a diode laser.
6. A vehicle lighting system according to claim 1, wherein said uniform thickness thin sheet optical element has a substantially linear crosssection.
7. A vehicle lighting system according to claim 1, wherein said uniform thickness thin sheet optical element has a predetermined curved cross-section.
8. A vehicle lighting system according to claim 1, wherein said uniform thickness thin sheet optical element is configured as an outer lens for a vehicle lamp.
9. A lighting system for use in an automotive vehicle, comprising:

a remote light source for generating light; at least one light guide having a first end and a second end, the first end being connected to said remote light source, for transmitting light from said remote light source; a uniform thickness thin sheet optical element having a front surface, a back surface with a plurality of microoptical wedges formed thereon for receiving and reflecting light through the front surface, and a perimeter side surface generally normal to the front surface with a side surface length; and at least one holographic extractor disposed along the perimeter side surface having a length substantially equivalent to the side surface length for receiving and transmitting light through the perimeter side surface toward the micro-optical wedges, the light having a predetermined uniform luminous intensity distribution after passing through the front surface.
10. A vehicle lighting system according to claim 9, wherein the redirected light passing through the perimeter side surface reflects off the front surface before being directed to the predetermined regions of the plurality of micro-optical wedges.
11. A vehicle lighting system according to claim 9, wherein said uniform thickness thin sheet optical element is comprised of a polymeric transparent optical material.
12. A vehicle lighting system according to claim 9, wherein said uniform thickness thin sheet optical element lo has a thickness between 1Ogm-6mm.
13. A vehicle lighting system according to claim 9, wherein said remote light source is a diode laser.

is
14. A vehicle lighting system according to claim 9, wherein said uniform thickness thin sheet optical element has a substantially linear cross- section.
15. A vehicle lighting system according to claim 9, wherein said uniform thickness thin sheet optical element has a predetermined curved cross-section.
16. A vehicle lighting system according to claim 9, wherein said uniform thickness thin sheet optical element is configured as an outer lens for a vehicle lamp.
17. A vehicle lighting system for use in an automotive vehicle, said vehicle lighting system comprising:

a remote light source for generating light; a plurality of light guides for transmitting light from said remote light source, each of said light guides having a first end and a second end, each first end of said light guides is connected to said remote light source; a uniform thickness thin sheet optical element having a front surface, a back surface with a plurality of micro optical wedges formed thereon for receiving and reflecting light through the front surface, and a perimeter side 12 surface generally normal to the front surface with a side surface length; and at least one holographic extractor disposed along the perimeter side surface having a light receiving end adjacent the second end and a length substantially equivalent to the side surface length for receiving and transmitting light through the perimeter side surface toward the microoptical wedges, the light having a predetermined uniform luminous intensity distribution after passing through the front surface; and a beam forming device disposed on the front surface.
18. A vehicle lighting system according to claim 17, wherein said beam forming device is chosen from the group holographic diffuser, pillow optical element, or diffractive optical element.
19. A vehicle lighting system according to claim 17, wherein said uniform thickness thin sheet optical element 2o has a predetermined curved crosssection.
20. A vehicle lighting system according to claim 17, wherein said uniform thickness thin sheet optical element is an outer lens for a vehicle lamp.
21. A vehicle lighting system substantially as hereinbefore described with reference to the accompanying drawings.