PATENT DOCUMENT

Publication Number: US-11130391-B2
Application Number: US-201615758660-A
Country: US
Kind Code: B2

Title: Active glare suppression system

Abstract:
A vehicle may have optical structures such as windows and mirrors that have the potential to allow glare from external objects to shine into the eyes of a driver or other vehicle occupant. A control circuit may gather information on where the eyes of the driver are located using a camera mounted in the vehicle and may gather information on where the sun or other source of glare are located outside of the vehicle. Based on this information, the control circuit may direct a light modulator on a window or mirror to selectively darken an area that prevents the glare from reaching the eyes of the driver. The light modulator may have a photochromic layer that is adjusted by shining light onto the photochromic layer, may be a liquid crystal modulator, an electrochromic modulator, or other light modulator layer.

Claims:
What is claimed is: 
     
       1. A system that reduces glare associated with exterior light shining into a vehicle, comprising:
 a sensor that gathers eye location information; 
 a first light source; 
 a second light source; and 
 a light modulator that includes a photochromic layer, wherein: 
 
       the photochromic layer comprises a material that selectively darkens where exposed to light from the first light source and that selectively is bleached where exposed to light from the second light source, and 
       the light modulator is configured to selectively expose an area of the photochromic layer to light from the first and second light sources, wherein the area exposed is based at least partly on the eye location information. 
     
     
       2. The system defined in  claim 1  wherein the first light source comprises an ultraviolet light source configured to electrically generate and steer the ultraviolet light. 
     
     
       3. The system defined in  claim 1  wherein the first light source comprises an array of individually addressable ultraviolet light-emitting elements, the system further comprising a vehicle mirror that receives ultraviolet light from the individually addressable ultraviolet light-emitting elements. 
     
     
       4. The system defined in  claim 1  further comprising a vehicle window, wherein the light modulator is coupled to the vehicle window. 
     
     
       5. The system defined in  claim 4  wherein the vehicle window is interposed between an interior region in the vehicle and an exterior region outside of the vehicle and wherein the light source is in the interior region. 
     
     
       6. The system defined in  claim 4  wherein the vehicle window is interposed between an interior region in the vehicle and an exterior region outside of the vehicle and wherein the light source is in the exterior region. 
     
     
       7. The system defined in  claim 1  further comprising a vehicle mirror, wherein the light modulator is coupled to the vehicle mirror. 
     
     
       8. The system defined in  claim 7  wherein the vehicle mirror has a first side that reflects the exterior light and has an opposing side that receives ultraviolet light from the first light source. 
     
     
       9. The system defined in  claim 7  wherein the vehicle mirror comprises a Bragg reflector through which ultraviolet light from the first light source passes. 
     
     
       10. The system defined in  claim 1  wherein the first light source comprises an ultraviolet light source and wherein the second light source is an infrared light source that is configured to apply infrared light to the photochromic layer. 
     
     
       11. The system defined in  claim 1  further comprising a filter layer. 
     
     
       12. The system defined in  claim 11  wherein the filter layer is configured to pass visible light and block ultraviolet light. 
     
     
       13. The system defined in  claim 1  further comprising at least one ultrasonic transducer configured to produce an acoustic Bragg grating. 
     
     
       14. The system defined in  claim 1  wherein the photochromic layer has an edge and wherein the second light source comprises an infrared light source that emits infrared light into the photochromic layer along the edge. 
     
     
       15. The system defined in  claim 1  wherein the glare is associated with light from an external object, the system further comprising one or more sensors that are configured to gather information on a direction from which the external object is projecting light towards a location associated with the eye location information and wherein the light modulator is further configured to selectively expose an area of the photochromic layer to light from the first light source at least partly based on the information on the direction from which the external object is projecting the light. 
     
     
       16. A vehicle mirror, comprising:
 a reflective layer that reflects visible light and transmits ultraviolet light; 
 a light source that produces light; and 
 a photochromic layer coupled to the reflective layer, wherein the photochromic layer comprises a material that selectively darkens where exposed to the light from the light source, wherein the reflective layer is interposed between the light source and the photochromic layer, and wherein the reflective layer is configured to pass light from the light source to the photochromic layer. 
 
     
     
       17. The vehicle mirror defined in  claim 16  wherein the reflective layer comprises a Bragg reflector. 
     
     
       18. The vehicle mirror defined in  claim 17  wherein the light source comprises an ultraviolet light source, the photochromic layer comprises a material that darkens in reaction to ultraviolet light, and the light from the light source comprises ultraviolet light that causes the photochromic layer to darken in a local area. 
     
     
       19. A vehicle window, comprising:
 a transparent layer; 
 an array of individually addressable light-emitting diodes that produces light; and 
 a photochromic layer on the transparent layer, wherein the photochromic layer comprises material configured to selectively darken where exposed to the light from a subset of the array of individually addressable light-emitting diodes. 
 
     
     
       20. The vehicle window defined in  claim 19  further comprising an infrared light source that is configured to apply infrared light to the photochromic layer to bleach the photochromic layer. 
     
     
       21. The vehicle window defined in  claim 19  further comprising a filter configured to allow visible light to pass and to block ultraviolet light.

Description:
This application claims priority to U.S. provisional patent application No. 62/221,524, filed Sep. 21, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to reducing glare and, more particularly, to reducing glare in vehicles. 
     Vehicles such as automobiles have a rear mirror and left and right side mirrors. Ambient light such as sunlight and light from headlights can reflect off of the mirrors and into the eyes of a driver. A driver may also be exposed to sunlight, light from headlights, and other sources of glare through the windows of a vehicle. Sunshades and window tinting may be used to reduce glare somewhat, but can be cumbersome and ineffective. 
     It would therefore be desirable to be able to provide improved ways in which to reduce glare in a vehicle. 
     SUMMARY 
     A vehicle may have structures such as windows and mirrors that have the potential to allow glare from external objects to shine into the eyes of a driver or other vehicle occupant. The windows may be side windows, front windows, windows on a vehicle roof, rear windows, or other suitable windows. The mirrors may be mounted on the left or right side of a vehicle (i.e., the mirrors may be vehicle mirrors such as side mirrors) and/or may be mounted in the interior of a vehicle to serve as a rearview mirror. A control circuit may gather eye location information indicating where the eyes of the driver are located using a sensor such as a camera mounted in the vehicle and may gather information on where an external object that produces glare such as the sun, a reflective portion of a vehicle (e.g., a shiny bumper or rear window on a vehicle on a roadway), a street lamp, or other source of glare is located outside of the vehicle and the direction in which the external (exterior) object is projecting light towards the vehicle (e.g., towards the eyes of a driver or other vehicle occupant). Based on this information, the control circuit may direct a light modulator on a window or vehicle mirror to selectively darken an area that prevents the glare from reaching the eyes of the driver. 
     The light modulator may be patterned to form a series of strips, rectangular regions, or areas of other shapes that extend along the upper edge of the front window of a vehicle and that therefore allow the light modulator to serve as an electrically adjustable sun shade. A light modulator may also be incorporated into other windows in a vehicle to reduce glare from headlights, the sun, and other light sources. Vehicle mirrors that are provided with light modulators can be adjusted to selectively darken a portion of the mirror that would otherwise reflect glare into the eyes of the driver. 
     A light modulator for a window or vehicle mirror may have a photochromic layer that is adjusted by shining light onto the photochromic layer, may be a liquid crystal modulator, may be an electrochromic modulator, or may be formed using other types of light modulator structures. The light modulator in a window or vehicle mirror may be supported on a transparent glass layer such as a glass layer in a vehicle mirror or vehicle window or may be supported by other support structures such as plastic and/or glass structures in vehicle windows or vehicle mirrors. 
     If desired, bleaching light may be used to photo-bleach photo-bleachable photochromic layers in light modulators. Arrays of light-emitting elements may be used to provide light to selectable areas of a photochromic layer in a photochromic light modulator. Arrays of electrodes may be used to apply control signals to light modulating cells in liquid crystal modulators, electrochromic modulators, and other light modulators that are controlled by applied electrical signals rather than applied light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a portion of an illustrative vehicle in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative vehicle or other system with glare reduction devices in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative window in which a portion may be locally darkened to reduce glare in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative mirror in which a portion may be locally darkened to reduce glare in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative steps involved in adjusting a glare reduction device in real time to reduce glare in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative sensor such as an image sensor system based on a stereo camera of the type that may be used to gather eye location information in accordance with an embodiment. 
         FIG. 7  is a perspective view of an illustrative window with locally darkened portions to reduce glare in accordance with an embodiment. 
         FIG. 8  is a perspective view of an illustrative window with a locally darkened portion to reduce glare in accordance with an embodiment. 
         FIG. 9  is a diagram of an illustrative window having horizontal regions that may be individually adjusted to modulate light transmission in accordance with an embodiment. 
         FIG. 10  is a diagram of a window of the type shown in  FIG. 9  in which the adjustable light modulation regions form an array with rows and columns in accordance with an embodiment. 
         FIG. 11  is a diagram of an illustrative steerable light source based on a light projector system in accordance with an embodiment. 
         FIG. 12  is a diagram of an illustrative steerable light source based on a laser or light-emitting diode that is oriented using a computer-controlled positioner in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of an illustrative steerable light source based on a steerable mirror in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative light source that emits light from a portion of a light guide layer in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a light guide layer that uses controllable protrusions to emit light at a controllable position along the surface of the light guide layer in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of a light modulator with a light guide layer that uses an array of adjustable-index-of-refraction cells to emit light into a photochromic layer at an adjustable location in accordance with an embodiment. 
         FIG. 17  is a cross-sectional side view of an illustrative mirror having a photochromic layer that is selectively illuminated in a given area from behind the mirror in accordance with an embodiment. 
         FIG. 18  is a cross-sectional side view of an illustrative mirror having a photochromic layer that is selectively illuminated in a given area a using an array of light sources located behind the mirror in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of an illustrative mirror having a photochromic layer that is selective illuminated from behind to darken a portion of the photochromic layer and that is bleached using a light source behind the mirror in accordance with an embodiment. 
         FIG. 20  is a cross-sectional side view of a light modulator having a photochromic layer and an illustrative light source based on a light concentrating structure with an electrically controlled shutter in accordance with an embodiment. 
         FIG. 21  is a cross-sectional side view of an illustrative light modulator having a photochromic layer that is locally darkened by a steerable light beam and that is bleached using blanket illumination in accordance with an embodiment. 
         FIG. 22  is a cross-sectional side view of an illustrative light modulator based on a liquid crystal cell in accordance with an embodiment. 
         FIG. 23  is a cross-sectional side view of an illustrative electrochromic light modulator in accordance with an invention. 
         FIG. 24  is a cross-sectional side view of an illustrative guest-host liquid crystal modulator in accordance with an embodiment. 
         FIG. 25  is a cross-sectional side view of an illustrative modulator such as a guest-host liquid crystal modulator in which the amount of light modulation that is produced varies as a function of position across the light modulator in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Systems such as vehicles and other systems may have transparent structures such as windows and reflecting structures such as mirrors. Sunlight and other light sources (e.g., headlights, street lights, etc.) can create undesired glare. Light modulating devices may be used to help block the glare. The light modulating devices may be incorporated into optical structures such as transparent and reflecting structures in the vicinity of a driver or other occupant of a vehicle or may be incorporated into optical structures in other environments that are prone to glare. 
     Light modulating devices may, for example, include a light modulating layer on the surface of a mirror to block undesired light from the sun or other light source. A light modulating layer may also be incorporated into a window to block undesired light. Electronic control systems may be used to determine an optimum location for the light blocking structures in a vehicle or other system and may adjust the light modulating devices accordingly. With this approach, the electronic control system and light modulator layer may serve as an active antiglare system. 
     An active antiglare system may be used in any suitable environment in which glare is present (e.g., in a boat, airplane, helicopter, motorcycle, train, truck, construction vehicle, or other vehicle, house, office, store, or other building, etc.). Antiglare layers may be formed on mirrors and/or windows or other optical layers that can serve as supporting surfaces for light modulators in these environments. Configurations in which antiglare layers are incorporated into the windows and/or mirrors in a vehicle are sometimes described herein as an example. 
     A side view of a portion of an illustrative vehicle of the type that may be provided with an antiglare system is shown in  FIG. 1 . As shown in  FIG. 1 , vehicle  10  may include a body such as body  12 . Body  12  may have body panels and other structures that are mounted on a chassis. Portions of body  12  may include doors. Interior components in vehicle  10  such as seating for a driver and other vehicle occupants may be supported by the chassis. External components such as wheels  18  may also be mounted to the chassis. The structures that make up body  12  may include metal structures, structures formed from fiber-composite materials such as carbon-fiber materials and fiberglass, plastic, and other materials. 
     Windows  14  may be formed at the front and rear of vehicle  10  in openings in body  12  and may be formed within the doors or other portions of the body  12  of vehicle  10 . As shown in  FIG. 1 , for example, vehicle  10  may have a front window such as front window  14 F that faces the front of vehicle, rearward facing windows such as rear window  14 R, and side windows such as windows mounted within the doors of vehicle  10  (see, e.g., side windows  14 D). Windows  14  may be formed from glass (e.g., glass laminated with polymer layers), plastics such as polycarbonate, or other clear materials. 
     Vehicle  10  may include vehicle mirrors  20 . Vehicle mirrors  20  may include side mirrors  20 - 1  on the left and right sides of vehicle  10  and rear view mirror  20 - 2 . 
     To reduce the glare experienced by a driver in vehicle  10 , transparent and reflective structures such as windows  14  and vehicle mirrors  20  may be provided with light modulator layers. The light modulator layers may be actively controlled by control circuitry in vehicle  10  using information on the location of light sources that are producing glare (glare location information), using information on the location of the driver&#39;s eyes (eye location information) and/or information on the direction from which exterior light is being projected towards the driver&#39;s eyes from the light sources (e.g., from the sun, headlights, reflective surfaces of vehicles and other objects, street lights, and other external objects that produce glare), and using the known locations of the light modulator layers (light modulator layer location information). Light modulation may be produced by illuminating a photochromic layer with light to selectively darken the photochromic layer or by otherwise modulating light transmission and/or reflection (e.g., by applying signals to appropriate electrodes in a light modulator that is electrically controlled using an array of electrodes). 
     A schematic diagram of an illustrative circuitry that may be used in operating vehicle  10  is shown in  FIG. 2 . As shown in  FIG. 2 , vehicle  10  may include control circuitry  30 . Control circuitry  30  may include storage and processing circuitry for supporting the operation of vehicle  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  30  may be used to control light modulators and other devices operating in vehicle  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, electronic control units, etc. 
     Vehicle  10  may include input-output devices  22  that allow data to be supplied to vehicle  10  and that allow data to be provided from vehicle  10  to external systems. Input-output devices  22  may include sensors  24  for gathering information on the operating environment of vehicle  10 . Sensors  24  may include light-based sensors, wireless sensors such as radar sensors, ultrasonic sensors, proximity sensors, range-finding sensors, ambient light sensors such as ambient light sensor  26  that measure that amount of light on the exterior of vehicle  10  and/or the interior of vehicle  10 , sensors such as camera  28  (e.g., stereoscopic cameras or other camera systems including digital image sensors and/or other light-based sensors or other sensors for detecting a user&#39;s head position, a user&#39;s eye position and/or a user&#39;s direction of gaze), strain gauges, parking sensors, cruise control sensors, accelerometers, touch sensors, magnetic sensors such as electronic compass sensors, temperature sensors, rain sensors and other moisture sensors, force sensors, pressure sensors (e.g., altimeters), and other components for making measurements on the environment surrounding vehicle  10 . 
     As shown in  FIG. 2 , input-output devices  22  may include user input-output devices  32 . Devices  32  may be used to gather input from users (e.g., a driver or passenger of vehicle  10 ) and may be used in providing output to users. Devices  32  may include buttons, joysticks, steering wheels, shift levels and/or buttons, foot-actuated controllers (e.g., a throttle pedal, a brake pedal, a clutch pedal, etc.), touch pads, keypads, keyboards, motion sensors, microphones, cameras, and other devices for gathering user input. Input devices in devices  32  may also circuitry for generating audio output such as speakers, tone generators, and vibrators and circuitry for generating visible output. 
     Light-based devices  34  may include internal devices and external devices for providing light-based output. Light-based devices  34  may include, for example, light sources  36 . Light sources  36  may include devices that produce light in response to applied electrical current such as lamps, light-emitting diodes and other status indicators, displays, lasers, arrays of light sources, individual light sources, backlight units for displays, light sources that emit one or more beams of light (e.g., a laser beam, light-emitting diode beam, or a beam associated with another collimated light source), light sources that emit light in a fixed pattern of one or more beams, light sources that emit light using raster scanning techniques, light sources that emit steerable beams (e.g., light sources with mirror arrays to steer light in a light projector system, light sources with one or more steerable mirrors, steerable lasers and light-emitting diodes, etc.), and other electrically controlled light sources. 
     Light modulators  38  may include mechanical and/or electrical modulators such as mechanical shutters, liquid crystal modulators (e.g., liquid crystal shutters having polarizers), modulators based on cholesteric liquid crystals or other structures that exhibit opaque (light scattering) and transparent modes, guest-host liquid crystal modulators, electrochromic modulators, light modulators based on electrically bleached and/or photo-bleached photochromic layers, and other light modulators. 
     Light-based devices  34  (e.g., light sources  36  and/or light modulators  38 ) may contain individually controlled areas. These areas may be relatively small areas that may serve as pixels in an array of pixels for a display-type output device (e.g., a heads-up display integrated into a window) and/or that create small antiglare patterns (e.g., small dark areas that shadow a driver&#39;s eyes from glare). If desired, the individually controlled areas may include one or only a few larger controlled areas (e.g., areas that are patterned to form electrically adjustable sun visor patterns or other antiglare patterns on a window, antiglare areas on mirrors, etc.). 
     Wireless circuitry  40  may include radio-frequency transceiver circuitry and antennas for transmitting and receiving wireless signals. The signals may include, for example, short-range signals such as wireless local area network signals (WiFi® and Bluetooth® signals) and long-range signals (e.g., cellular telephone signals and other signals at frequencies of 700 MHz to 2700 MHz and/or other suitable frequencies). Wireless information may be shared with nearby vehicles, sensors and beacons embedded along a roadway, satellites, cellular telephone networks, cellular telephones, wristwatches, and other wireless devices associated with a driver and passengers in vehicle  10 , etc. Wireless information that is received by circuitry  40  may include traffic information, weather information, information on the status of nearby vehicles (e.g., direction of motion, acceleration/deceleration, brake status (braking due to application of brakes by a driver or not braking), throttle status (applied or not applied), temperature information, road condition information (as measured by sensors in vehicles and/or external sensors), etc. 
     Vehicle controls  42  may include control circuitry, actuators, and other systems for controlling vehicle operation. Vehicle controls  42  may include systems for steering, braking (manual brakes, emergency brakes, power-assisted brakes, drum brakes, disc brakes, regenerative brakes that use drive motors or other systems to recover energy and convert the kinetic energy of vehicle  10  into electrical energy stored in capacitors and/or batteries or that use other techniques for storing recovered energy, or other braking systems), accelerating, shifting gears, adjusting interior and exterior lights, adjusting infotainment functions, controlling satellite navigation system operation, adjusting airbags, seatbelts, and other safety devices, controlling audio output, controlling electronic windows, door locks, the opening and closing of doors and hatches, windshield wipers, defrosters, and other climate controls, and systems for controlling and adjusting other operations during the operating of vehicle  10 . 
     Using information from sensors  24 , user input from devices  32  and other input from devices  22 , and/or information received wirelessly from remote sources via wireless circuitry  40 , vehicle  10  may take actions to reduce the amount of light reaching a driver or other occupant of vehicle  10 . For example, control circuitry  30  may use sensors  24  to determine that the sun is shining in the upper portion of the front window directly towards the eyes of the driver. In this situation, control circuitry  30  may direct a light modulator on the front window to selectively darken a portion of the front window that lies directly between the sun and the driver&#39;s eyes, thereby shadowing the driver&#39;s eyes from the glare of the sun. As another example, a vehicle that is located behind the driver&#39;s vehicle may be shining its headlights into vehicle mirrors  20 . Control circuitry  30  may use sensors  24  to detect this light and to direct a light modulator in the mirror to create darkened areas that prevent reflection of the light into the eyes of the driver. The non-darkened portions of the windows and mirrors in these types of scenarios remain in their normal state, so that the driver can continue to observe the surroundings of the vehicle. 
     An illustrative scheme for reducing glare using a light modulator incorporated into a transparent layer such as a window is shown in  FIG. 3 . In the example of  FIG. 3 , external light source  60  is producing unwanted glare (i.e., light beam  62 ) that is directed towards the eyes of the driver (see, e.g., eye  64 ). A sensor such as camera  28  or other suitable sensor may monitor the face of the driver to identify the location of the driver&#39;s eyes. Control circuitry  30  may obtain information on the location of external sources of glare such as external light source  60  by using an externally mounted sensor such as camera  28 ′ (or other light detector) to measure the position of external light source  60 . If desired, sun position information may be calculated using information on the location and orientation of vehicle  10  and on the current time and date (e.g., using orientation information from a rotation sensor that is Kalman-filtered using output from a Global Positioning System (GPS) receiver to establish reliable low frequency orientation data, GPS information, compass heading information, accelerometer information, or other orientation sensor information, information from a clock, etc.). Information on the location of the headlights of other vehicles relative to vehicle  10  may be established using wireless communications (e.g., using vehicle-to-vehicle communications, etc.). By using information on the location of eyes  64  (eye location information) and/or information on the direction from which external object (glare source)  60  is projecting light toward eyes  64  and by using information on the location of glare source  60  (glare location information) in combination with the known location of the light modulator on window  14  (light modulator location information), control circuitry  30  can determine an optimum location for locally darkening window  14 . As shown in  FIG. 3 , for example, portion  14 ′ of window  14  may be darkened to block light  62  from light source  60  and thereby shield eyes  64  from light  62  without blocking the driver&#39;s view of external objects such as object  82  (e.g., objects on the road on which vehicle  10  is being drive). 
     With one suitable arrangement, window  14  may include a layer of photochromic material that changes from transparent to opaque (e.g., black, white, etc.) when exposed to light  70 . Light  70  may be ultraviolet light or light with other suitable wavelengths (e.g. infrared, visible light of appropriate wavelengths, etc.). Ultraviolet light  70  may be generated by a light source such as an electrically controlled light source  36  in vehicle interior  66  or an electrically controlled light source  36  in exterior region  68 . 
     As shown in  FIG. 4 , this type of light-based modulation scheme may be used in a mirror. In the example of  FIG. 4 , a driver is looking at mirror  20  in direction  72 . Light  62  from the sun or other light source  60  may have the potential to reflect from mirror  20  into the eyes of the driver in region  76  in front of mirror  20  (see, e.g., eye  64  of  FIG. 4 ). To block this potential glare, region  38 ′ of light modulating layer  38  may be selectively darkened (i.e., rendered opaque). Layer  38  may be a light modulation layer based on a layer of photochromic material that is darkened when exposed to light  70  from one or more light sources  36 . Light sources  36  may be located in region  76  in front of mirror  20  or in region  74  behind mirror  20 . A reflective layer such as layer  80  may be interposed between light source  36  in region  74  and layer  38  to create a reflective surface for mirror  20  (i.e., a reflective layer that reflects visible exterior light). 
     Reflective layer  80  may be formed from a series of dielectric layers (e.g., inorganic dielectric layers and/or organic dielectric layers) with different indices of refraction. For example, reflective layer  80  may be formed from a series of alternating high-index-of-refraction and low-index-of-refraction layers that form a Bragg reflector. The sublayers that make up the Bragg reflector (i.e., the layers that make up reflective layer  80 ) may be configured to reflect visible light (so that mirror  20  reflects visible light for the driver) while passing light  70  (e.g., while passing ultraviolet light  70  or light  70  of other wavelengths to layer  38 ). This allows light  70  from behind mirror  20  to pass through layer  80  and illuminate a selected portion of photochromic layer  38  to form darkened portion  38 ′. 
       FIG. 5  is a flow chart of illustrative steps involved in using a light modulator to reduce glare in vehicle  10 . 
     At step  84 , information may be gathered on the operating environment of vehicle  10 . For example, sensors such as camera  28  may be used to determine where the driver of vehicle  10  is located, where the head of the driver is located, and wherein the eyes of the driver are located. The direction of the driver&#39;s gaze may be determined by analyzing images of the driver&#39;s head and eyes. For example, control circuitry  30  can use information from camera  28  to determine whether the user is viewing external objects through front window  14 F or other windows  14  in vehicle  10 , whether the user is viewing objects that have been reflected from mirrors  20 , etc. In addition to determining the location of the driver&#39;s eyes and/or the direction of the driver&#39;s gaze (i.e., the direction in which the driver is looking), control circuitry  30  can use other sensors  24  such as ambient light sensors, external cameras such as cameras  28 ′ of  FIGS. 3 and 4 , and can use information on the time of day, vehicle location, orientation, direction of travel, etc. (e.g., information from an orientation sensor, Global Positioning System receiver or other satellite navigation system receiver, clock, etc.), to determine where external light sources such as source  60  are located relative to windows  14 , mirrors  20 , and the driver&#39;s eyes (and/or the driver&#39;s viewing direction). 
     Based on knowledge of these factors (e.g., driver viewing direction and/or driver eye location, light source location, and the known location of intervening optical structures such as windows  14  and mirrors  20  that incorporate light modulating structures), control circuitry  30  can calculate the locations of the regions of the light modulating structures in vehicle  10  that should be modified to block glare from light source  60 . In particular, at step  86 , control circuitry  30  can determine which areas of transparent structures such as windows  14  and which areas of reflective structures such as mirrors  20  should be darkened (or otherwise provided with reduced light transmission properties). 
     After determining which portions of the light modulating layer(s) of windows  14  and/or mirrors  20  should be adjusted, control circuitry  30  may, at step  88 , supply corresponding control signals to the light modulating structures of windows  14  and/or mirrors  20  at step  88 . For example, control circuitry  30  can modulate the light transmission properties of a region of a light modulator layer in window  14  to produce reduced transmission region  14 ′ of  FIG. 3  and/or may reduce the transmission of a portion of layer  38  of mirror  20  of  FIG. 4  to produce reduced-transmission portion  38 ′. Light modulation (e.g., light transmission adjustments) of selected portions of a light modulator layer in a window or mirror may be accomplished using electrical control (e.g., applying a voltage to an electrode in a light modulator to adjust a direct-current or alternating-current electric field), by applying heat (e.g., by applying a current to a heating electrode), by applying light  70  to a photochromic layer (see, e.g., light  70  from light sources  36  of  FIGS. 3 and 4 ), by controlling magnetic fields applied to nano-ferromagnetic fluids, or by otherwise applying a stimulus to a selected portion of a light modulator layer. By decreasing the light transmission of appropriate portions of a window or mirror in this way, glare (undesired light  62 ) that reaches the eyes of the driver may be minimized. As indicated by line  90 , these glare reduction activities may be performed continuously during operation of vehicle  10 . 
     Camera  28  may be a stereo camera having two or more individual image sensors, as shown by left camera  28 - 1  and right camera  28 - 2  in  FIG. 6 . The individual cameras in camera system (camera)  28  of  FIG. 6  may be used to perform triangulation operations that help control circuitry  30  accurately determine the location of driver  92 , the driver&#39;s eyes (eyes  64 ), and the direction of view of the driver (direction of view  94  in the example of  FIG. 6 ). Other types of imaging systems and sensors may be used in determining the direction of the driver&#39;s view. Moreover, other sensing techniques (e.g., three-dimensional sensing techniques) may be used such as sensing techniques based on patterned illumination, lidar, and time-of-flight images. The illustrative stereo camera of  FIG. 6  is merely illustrative. If desired, cameras such as stereo camera  28  of  FIG. 6  may be used outside of vehicle  10  (see, e.g., cameras  28 ′ of  FIGS. 3 and 4 ). 
       FIGS. 7 and 8  are perspective views of illustrative light modulator layers  96  (e.g., light modulators in windows  14 ). As shown in  FIG. 7 , multiple individual portions of layer  96  such as portions  96 - 1  and  96 - 2  may be darkened based on the measured positions of the driver&#39;s eyes  64 . Portions  96 - 1  and  96 - 2  may be darkened to block light from light source  60  (i.e., when a driver&#39;s eyes  64  are looking in direction  94 - 1 ) while remaining undarkened portions of layer  96  allow the driver to view external objects such as object  82  (i.e., when a driver&#39;s eyes  64  are looking in direction  94 - 2 ). If desired, the light blocking portion of light modulator layer  96  may form a single uninterrupted region such as region  96 - 3  of  FIG. 8 . Other types of light blocking areas may be used to reduce glare, if desired. The illustrative configuration of  FIG. 7  in which each reduced-transmission area (area  96 - 1  and  96 - 2 ) is associated with a respective one of eyes  64  and the illustrative configuration of  FIG. 8  in which a single reduced-transmission area (area  96 - 3 ) shadows both eyes  64  from glare from light source  60  are merely illustrative. 
       FIG. 9  is a diagram of an illustrative structure in vehicle  10  such as window  14 . Window  14  may be provided with a light modulating layer that can be used to reduce the transmission through one or more selected areas to reduce glare. In the example of  FIG. 9 , window  14  has top edge  14 T, bottom edge  14 B, and respective left and right edges  14 L and  14 R. Window  14  may be a front window, rear window, or side window in vehicle  10 . Window  14  may have electrodes or other structures to facilitate the formation of an electronically adjustable sun visor. In particular, a light modulator may be incorporated into window  14  that allows one or more areas such as areas  96 A,  96 B,  96 C, . . . to be selectively darkened (by the same amount or by progressively increasing amounts or other different amounts). 
     As an example, in a dark and glare-free environment, all of areas  96 A,  96 B,  96 C, . . . may be adjusted to exhibit maximum transmission (i.e., all areas of layer  96  may be clear). When the sun or other source of glare is at a high elevation with respect to window  14 , only the uppermost portion of layer  96  can be darkened (see, e.g., darkened area  96 A in  FIG. 9 ). When the sun or other source of glare is at a lower angle, more portions of layer  96  can be darkened (e.g., portions  96 A and  96 B can be darkened or portions  96 A,  96 B, and  96 C can be darkened). 
     In the illustrative arrangement of  FIG. 9 , the portions of window  14  that are being adjusted have the shape of elongated horizontal regions such as rectangular strips that run parallel to upper edge  14 T of window  14 . As shown in  FIG. 10 , an electronically adjustable sun visor may be formed using smaller regions such as regions  96 G. In the  FIG. 10  example, regions  96 G′ have been darkened to block glare in the upper left portion of the driver&#39;s field of view. When making adjustments that affect the driver&#39;s field of view, anti-glare regions may be selected that do not interfere with the driver&#39;s primary lines of sight (i.e., the driver&#39;s window directly in front of the driver&#39;s head will not be blocked, etc.). Adjustable regions of the type shown in  FIG. 10  may be used to provide a driver and a passenger in vehicle  10  with individually adjustable regions. Combinations of horizontal light modulator strips (as shown in  FIG. 9 ) and smaller light modulator regions (as shown in  FIG. 10 ) and/or other modulator patterns may be used, if desired. The examples of  FIGS. 9 and 10  are merely illustrative. The adjustable regions of the light modulator layers of  FIGS. 9 and 10  may be associated with individually controlled electrodes (e.g., in a liquid crystal modulator, electrochromic modulator, or other electrically controlled modulator), may be associated with regions of potential light illumination (e.g., portions of a photochromic layer that can be illuminated with ultraviolet light using light guide structures, beam steering structures, light-emitting diode arrays, or other optical structures), or other individually adjustable light modulator structures. 
     In photochromic light modulators, light source  36  may apply light  70  when it is desired to darken a portion of a photochromic layer. The area in which light source  36  applies light  70  may be controlled by control circuitry  30 , so that control circuitry  30  can control which portions of a window or mirror are selectively darkened. With one suitable arrangement, control circuitry  30  may supply signals to light source  36  that direct light source  36  to steer a beam of output light (light  70 ) in a desired direction. 
     In the example of  FIG. 11 , light source  36  is a steerable beam light source that produces a beam of light  70  that may be steered in directions such as directions  100 . Light emitter  102  (e.g., a light source such as a laser, lamp, or light-emitting diode) may emit light  70 - 1  (e.g., ultraviolet light or other suitable light). Modulator array  104  may have an array of microelectromechanical systems (MEMs) mirrors or other adjustable reflective micro-mirrors  104 ′. Mirrors  104 ′ can be individually adjusted to steer light  70 - 1 , thereby producing steered reflected light beam  70 - 2 . Optical systems such as lens structures  106  may be used to collimate and otherwise adjust light  70 - 2 , thereby producing steerable output beam  70 . Steerable light beam sources such as light source  36  of  FIG. 11  may sometimes be referred to as projector light sources or projector systems. 
     In the example of  FIG. 12 , the orientation of light emitter  102  of light source  36  is being adjusted by electrically controllable positioner  110 . Positioner  110  may be a stepper motor, a linear electromagnetic actuator, or other positioner that can control the angular orientation and/or the linear position of light emitter  102  and thereby steer output light beam  70  in desired directions such as directions  100 . 
     Another type of system for producing a steerable beam of output light is shown in  FIG. 13 . As shown in  FIG. 13 , steerable-beam light source  36  of  FIG. 13  may have a light emitter such as light emitter  102  that emits a beam of light such as beam  70 - 1  that is reflected from mirror  112  to produce light beam  70 . The orientation of mirror  112  may be adjusted using electrically controllable positioner  110 , thereby steering light beam  70  in directions  100 . 
     If desired, light emitter  102  may emit light  126  into a light guide structure such as illustrative light guide layer  114  of  FIG. 14 . Light  126  that has been emitted from light emitter  102  may be guided within light guide layer  114  in accordance with the principal of total internal reflection. Light guide layer  114  may be formed from a layer of transparent material (e.g., glass, plastic, quartz, fused silica, sapphire, or other clear materials). Light  70  may be scattered out of light guide layer  114  at a desired location by light scattering features  116 . Light scattering features  116  may be formed from protrusions, depressions, index-of-refraction discontinuities, metal structures, printed ink, or other structures that help scatter light  70  from light guide layer  114 . Light scattering features  116  may be formed at one or more fixed locations on light guide layer  114  or may be formed in electrically controllable locations (e.g., by forming cells with index of refraction characteristics that are electrically adjustable, etc.). Layer  114  may be stacked with other layers on a mirror or window (e.g., in a stack with a photochromic layer, etc.) to form a window or mirror with an integrated light modulator layer. 
     As shown in  FIG. 15 , light guide layer  114  may be separated from another transparent layer such as layer  120  by a gap such as gap  122 . Gap  122  may be filled with air or other material having an index of refraction that differs from that of layers  120  and  114 . For example, gap  122  may be formed from air or other material that has an index of refraction that is less than layers  120  and  114 . Using an electrically controllable actuator or other mechanism, a protrusion such a protrusion  118  may be formed in layer  120  that bridges gap  122 . In this portion of light guide layer  114 , there is no index-of-refraction discontinuity at the interface between layer  114  and gap  122 , so light  126  may escape out of layer  114  and pass through layer  120  to form emitted light  70 . 
     Structures of the type shown in  FIGS. 14 and 15  and other structures including light guide layers such as layer  114  may be incorporated into light modulators with photochromic layers. The light guide layer and associated structures for emitting light  70  from a desired portion of the light guide layer may be used in selectively darkening a portion of the photochromic layer. 
     An illustrative window for vehicle  10  that has been formed from a photochromic light modulator that can be illuminated with light from a light guide layer is shown in  FIG. 16 . In the example of  FIG. 16 , layers  130  may be used to selectively emit light  70  into region  122 ′ of photochromic layer  122 , thereby darkening region  122 ′ to reduce glare. Window  14  may have a transparent support layer such as layer  128  (e.g., one or more layers of glass and/or plastic laminated together to form a structural support layer for window  14 ). Light guide layer  114  may be formed from a layer of material on the inner surface of window layer  128 . Light  126  from light-emitter  102  (e.g., ultraviolet light, etc.) may be emitted into light guide layer  114  and may travel through light guide layer  114  in accordance with the principal of total internal reflection. 
     Layers  130  may include an array of liquid crystal cells  119 . Cells  119  may be formed from a layer of liquid crystal material. Transparent electrodes such as an array of cell-sized transparent electrodes  121  may be formed on the inner surface of photochromic layer  122  or other suitable substrate. A blanket conductive film on the outer surface of light guide layer  114  may form transparent ground electrode  117 . The index of refraction of each liquid crystal cell  119  may initially be lower than the index of refraction of layers  114  and  122 . To adjust the index-of-refraction of a given one of cells  119 , a voltage may be applied between the electrode  121  that is associated with that cell and ground electrode  117 . This creates an electric field that adjusts the index of refraction of the given cell. For example, the index of refraction of material  119 ′ may be increased to a value that matches that of layer  114  and that of layer  122 . In this scenario, total internal reflection will be locally defeated in the portion of window  114  that is overlapped by cell  119 ′. As a result, light  70  will leak out of cell  119 ′ into region  122 ′ of photochromic layer  122  and will darken region  122 ′. Filter layer  124  may be used to block stray light  70 . For example, filter layer  124  may be a filter that passes visible light and blocks ultraviolet light, thereby preventing ultraviolet light  70  from reaching the eyes of the driver (eye  64 ). Filter layers such as ultraviolet light blocking layer  124  may also be used in light modulators in windows and mirrors to help prevent ambient ultraviolet light from prematurely darkening a photochromic layer. For example, filter layer  124  may be placed on one side of a photochromic layer to block ambient ultraviolet light whereas a beam of ultraviolet light  70  may be selectively applied to the photochromic layer from the other side of the photochromic layer. 
     If desired, light extraction from layer  114  may be controlled using acoustic Bragg gratings. For example, an array of ultrasonic transducers may be located around the periphery of layer  114  and may be used to produce a strong acoustic Bragg grating over the region to be darkened. The Bragg grating helps extract light  116  from layer  114  into the portion of layer  122  to be darkened. 
       FIG. 17  is a cross-sectional side view of an illustrative mirror for vehicle  10  (e.g., a side vehicle mirror, a rearview vehicle mirror, or other mirror in vehicle  10 ). In the configuration of  FIG. 17 , mirror  20  has a reflective layer such as Bragg reflector layer  80  formed from a series of stacked alternating high-index-of-refraction and low-index-of-refraction layers  80 ′. This arrangement may be used to form a reflective layer that is highly reflecting at visible wavelengths. A driver may therefore view reflections of the driver&#39;s surroundings in mirror  20 , as indicated by reflected visible light  132 . Sublayers  80 ′ may be configured to pass ultraviolet light such as ultraviolet light  70  to photochromic layer  122 . Light source  136  may provide output beam  70  (e.g., using a light beam steering arrangement of the type shown in  FIGS. 11, 12, and 13 , using a planar light guide layer arrangement for distributing light  70  as described in  FIGS. 14, 15, and 16 , using an array of light-emitting elements, or by using other suitable light source configuration). Light  70  may be directed to layer  122  through Bragg reflector layer  80  (i.e., from the rear of mirror  20 ). By applying light  70  to a desired region of photochromic layer  122  through Bragg reflector layer  80 , that region of photochromic layer  122  may be locally darkened, as shown by darkened region  122 ′ of layer  122 . Filter layer  124  may be used to block ultraviolet light  70 , thereby preventing ultraviolet light  70  from reaching the eyes of the occupants of vehicle  10  (see, e.g., eye  64  of  FIG. 17 ). Stray ultraviolet light may be prevented from reaching the rear of layer  122  by enclosing mirror  80  (e.g., the rear of mirror  80 ) in an opaque mirror housing. 
     In the illustrative configuration of  FIG. 18 , light  70  is supplied from light source elements  36 E of light source  36 . Light source  36  may be, for example, an array of ultraviolet light-emitting diodes  36 E that are individually addressable. Control circuitry  30  can illuminate a subset of elements  36 E to create a desired pattern of output light  70 . Light  70  may pass through Bragg reflector layer  80  to illuminate and darken region  122 ′ of photochromic layer  122 . Ultraviolet light blocking layer  124  or other filter layer may be used to filter out light  70  while allowing reflected light  132  to pass to and reflect from reflecting layer  80 . 
     Photochromic layers in light modulators for mirrors and windows may be returned to their undarkened state by halting the application of light  70 . If desired, bleaching light may be applied to the photochromic layer to help return a darkened portion of the photochromic layer to an undarkened state. As an example, light at a first wavelength (e.g., ultraviolet light  70 ) may be used to convert a bistable photochromic dye in the photochromic layer from its transparent state to an opaque state. When it is desired to return the darkened region of the photochromic layer to its transparent state, light at a second wavelength (e.g., visible light or infrared light) may be applied to bleach the photochromic dye. The photochromic dye in this type of arrangement may be a p-type photochromic dye. 
     An illustrative configuration for mirror  20  that is based on a light bleached photochromic layer is shown in  FIG. 19 . As shown in  FIG. 19 , mirror  20  may have a reflective layer such as Bragg reflector  80 . Bragg reflector  80  may reflect visible light  132  to allow the structures of  FIG. 19  to serve as a mirror. Bragg reflector layer  80  may be configured to allow ultraviolet light and infrared light to pass through layer  80 . When it is desired to darken a portion of photochromic layer  122 , selected light-emitting elements  36 E of layer  36  may emit ultraviolet light  70  into that portion of layer  122  (see, e.g., darkened portion  122 ′ of layer  122 ). Light for bleaching region  122 ′ may be supplied from light source  140  (e.g., a visible or infrared light source that emits light into layers  122  along one of the edges of layer  122 ) and/or from bleaching light source  142 . Source  142  may contain an array of light-emitting elements  142 E in a layer on the rear of mirror  20  or may be formed from a single element (or multiple elements) such as a stand-alone light-emitting diode that is not formed as part of a layer of light-emitting elements. Source  142  may supply bleaching light that passes through reflector layer  80  to bleach region  122 ′ of photochromic layer  120 . The light from bleaching light source  142  may be infrared light that passes through Bragg reflector  80 . If desired, Bragg reflector  80  may be configured to pass a narrow band of visible light wavelengths. The pass band may be aligned with the wavelength of bleaching light emitted by light source  142 , so that light from bleaching light source  142  can pass through Bragg reflector  80  to bleach photochromic layer  122 . The pass band may be sufficiently narrow to allow most visible light on the front of mirror  20  to be reflected (see, e.g., light  132  of  FIG. 19 ). 
     If desired, a light concentrator such as light concentrator  150  of  FIG. 20  may be used to gather and concentrate sunlight or other ambient light. This concentrated light may then be used to form light that darkens portions of photochromic layer  122  or light that bleaches photochromic layer  122  in a mirror or window. A liquid crystal shutter or other electrically controllable or mechanically controlled shutter such as shutter  152  may be used to adjust the amount of light  160  (e.g., sunlight) that enters light concentrator  150 . Shutter  152  may receive control signals from control circuitry  30  on transparent electrodes  154  (e.g., indium tin oxide electrodes) via terminals  156 . 
     The state of the signals on electrodes  154  may control the amount of light transmission through shutter  152  to light concentrator  150 . When shutter  152  is closed, none of light  160  reaches light concentrator  150  and therefore no light is distributed to layer  122  via light guide layer  158 . When shutter  152  is open, light  160  may be distributed to photochromic layer  122  via light guide layer  158 . If desired, light modulator structures with arrays of electrodes or other structures may be interposed between light guide  158  and layer  122  and used to determine which regions of layer  122  receive light from light guide layer  158  (see, e.g., arrangements of the type described in connection with  FIGS. 14, 15, and 16 ). 
     In the illustrative arrangement of  FIG. 21 , light from light source  36  (e.g., a steerable beam light source producing ultraviolet light  70 ) is being used to selectively darken portion  122 ′ of photochromic layer  122 . Layer  122  may be incorporated into a mirror or window. When it is desired to bleach portion  122 ′, bleaching light  170  (e.g., infrared light) may be emitted into light guide layer  172  from bleaching light source  174  (e.g., a light-emitting diode emitting bleaching visible or infrared light). Reflector  176  may be used to help recycle light  170 . Light scattering features in layer  172  may scatter a portion of light  170  into layer  122  to bleach layer  122 . In photo-bleaching arrangements such as the illustrative photo-bleaching arrangement of  FIG. 21 , photochromic layer  122  is preferably formed from a photo-bleachable (p-type) photochromic dye. 
     If desired, an electrically adjustable sun visor such as the light modulating structures of  FIGS. 9 and 10  or other light modulator for reducing glare through windows  14  or in mirrors  20  may be formed using individually adjustable light modulator cells controlled by applied electric signals. These cells may be formed from liquid crystal shutter structures or other individually addressable light modulators and may be formed in any suitable pattern across windows  14  and/or mirrors  20 . 
     A cross-sectional side view of an illustrative light modulating cell in a liquid crystal light modulator layer is shown in  FIG. 22 . As shown in  FIG. 22 , light modulator  178  includes liquid crystal layer  186  sandwiched between transparent conducting electrodes  184  and  188  (e.g., indium tin oxide electrodes). Electrode  184  may be formed on substrate  182  and electrode  188  may be formed on substrate  190 . Substrates  182  and  190  may be clear transparent layers of material such as plastic or glass. Layers  182 ,  184 ,  186 ,  188 , and  190  may be sandwiched between polarizers  180  and  192 . The amount of voltage applied across electrodes  184  and  188  controls the electric field in layer  186 , which controls the polarization of light passing through layer  186 . In conjunction with the operation of polarizers  180  and  192 , this allows voltage adjustments on electrodes  184  and  188  to control the amount of light  194  that passes through modulator  178  to form transmitted light  196 . When a first voltage is applied, for example, transmission may be high (i.e., modulator  178  may be transparent and the intensity of light  196  may equal the intensity of light  194 ). When a second voltage is applied, transmission may be low (i.e., modulator  178  may be darkened so that the intensity of light  196  is significantly reduced relative to that of light  194 ). Multiple different adjustment levels may be supported (e.g., to provide areas that are black, other areas that are gray, and yet other areas that are light gray). Gaps between individual indium tin oxide electrodes may be filled with an index-matched insulator or structures of the type shown in  FIG. 22  may be embedded in an index-matched substrate to reduce light scattering and diffraction. 
     Another type of electrically controllable light modulator cell that may be used in forming glare reducing light modulator structures for windows  14  and mirrors  20  is shown in  FIG. 23 . Light modulator cell  200  of  FIG. 23  is based on an electrochromic device. The electrochromic structures of cell  200  include electrodes such as electrode  202  and electrode  210 . Electrodes  202  and  210  may extend along lateral dimensions X and Y that lie perpendicular to dimension Z. Electrode  202  is adjacent to electrochromic layer  204  and electrode  210  is adjacent to electrochromic layer  208 . A current may be applied to electrochromic layers  204 ,  206 , and  208  to either darken (color) or lighten (discolor) cell  200 . Layers  204 ,  206 , and  208  may be, for example, materials that support an oxidation-reduction reaction in which the polarity of the applied electrical signal determines whether cell  200  is darkened or lightened. By increasing or decreasing the transmission of the light modulating layer of cell  200 , the amount of light  212  that passes through cell  200  can be controlled. 
     With one illustrative configuration, electrochromic material  204  is a layer of Li x NiO formed as a coating on electrode  202 , electrochromic material  208  is a layer of WO 3  formed as a coating on electrode  210 , and material  206  is a layer of a gel electrolyte such as LiNiOP that is interposed between the Li x NiO and WO 3  layers. With this type of configuration, cell  200  can be darkened or lightened by applying current through layers  204 ,  206 , and  208  using electrodes  202  and  210 . The NiO material of layer  204  is brownish in color when undoped, but turns transparent when doped with Li. The WO 3  material of layer  208  is bluish in color when doped by Li, but turns transparent when not doped by Li. When it is desired to darken cell  200 , a positive voltage may be applied to electrode  202  relative to electrode  208 . This causes Li+ ions to be injected into electrolyte layer  206  from layer  204  and causes Li+ ions to form LiWO 3  complexes at the interface between layers  206  and  208 , thereby coloring both layers  204  and  208  and darkening cell  200 . When it is desired to render cell  200  transparent, a negative voltage may be applied to electrode  202  relative to electrode  210 . This causes Li+ ions to be injected into layer  206  from layer  208 , leaving behind undoped WO 3  in layer  208  and causes LiNiO complexes to form at the interface between layers  204  and  206 , thereby uncoloring both layers  204  and  208  and rendering cell  200  transparent. 
     Guest-host liquid crystal devices may also be used to form liquid crystal light modulators for reducing glare in windows  14  and mirrors  20 . An illustrative guest-host liquid crystal modulator is shown in  FIG. 24 . As shown in  FIG. 24 , modulator layer  214  may have a guest-host liquid crystal layer such as layer  222  interposed between substrate layers  216  and  226 . Transparent electrodes  218  and  224  (e.g., indium tin oxide electrodes) may be formed on substrates  216  and  226 . The state of the modulator cell formed from layer  214  may be adjusted by adjusting the alternating current signal applied to electrodes  218  and  224 . When control circuitry  30  directs signal source  220  to apply a first signal, layer  214  may be transparent and when control circuitry  30  directs signal source  220  to apply a second signal, layer  214  may be opaque (e.g., darkened to block glare for a window or mirror). Modulator cells such as the illustrative cells of  FIGS. 22, 23, and 24  or other suitable modulator cells may be patterned in modulator patterns of the type shown in  FIG. 9  and  FIG. 10  (e.g., to implement an electrically adjustable sun visor), may be formed in an array of rectangular pixels that covers all of a mirror or window (e.g., to form an active glare reducing matrix with individually addressable darkened areas), or may be used in any other portion of a light modulator structure to reduce glare in windows and mirrors for vehicle  10  or other suitable system. 
       FIG. 25  is a cross-sectional side view of an illustrative wedge shape guest-host liquid crystal modulator. Modulator  214  of  FIG. 25  may be controlled by controlling the signal applied to electrodes  218  and  224  as described in connection with modulator  214  of  FIG. 24 . Due to the increased thickness of liquid crystal layer  222  at end  222 - 1  relative to end  222 - 2 , end  222 - 1  will darken more than end  222 - 2  during modulation. This type of arrangement may be used to provide a modulation gradient (i.e., a sun visor “tint” that is darker near upper edge  14 T of window  9  and that is progressively lighter at increasing distances into window  14  from edge  14 T). Light modulators based on other light modulation technology may also be provided with regions of different thickness (and therefore light modulation). The example of  FIG. 25 , which is based on a guest-host liquid crystal modulator, is merely illustrative. 
     In accordance with an embodiment, a system for a vehicle that reduces glare associated with exterior light shining into the eyes of an occupant of the vehicle is provided that includes a sensor that gathers information on the eyes, and a light modulator that includes a photochromic layer, a light source configured to selectively darken an area of the photochromic layer, and a source of additional light that is configured to bleach the darkened area of the photochromic layer, the light modulator is configured reduce the light by selectively darkening the area based at least partly on the information. 
     In accordance with another embodiment, the light source includes an electrically steerable ultraviolet light source configured to generate and steer the ultraviolet light. 
     In accordance with another embodiment, the light source includes an array of light-emitting elements. 
     In accordance with another embodiment, the system includes a vehicle window, the light modulator is coupled to the vehicle window. 
     In accordance with another embodiment, the vehicle window is interposed between an interior region in the vehicle and an exterior region outside of the vehicle and the light source is in the interior region. 
     In accordance with another embodiment, the vehicle window is interposed between an interior region in the vehicle and an exterior region outside of the vehicle and the light source is in the exterior region. 
     In accordance with another embodiment, the system includes a vehicle mirror, the light modulator is coupled to the vehicle mirror. 
     In accordance with another embodiment, the vehicle mirror has a first side that reflects the light and has an opposing side that receives ultraviolet light from the light source. 
     In accordance with another embodiment, the vehicle mirror includes a Bragg reflector through which ultraviolet light from the light source passes. 
     In accordance with another embodiment, the light source includes an ultraviolet light source and the source of the additional light is an infrared light source that is configured to apply infrared light to the photochromic layer. 
     In accordance with another embodiment, the system includes a filter layer. 
     In accordance with another embodiment, the filter layer is configured to pass visible light and block ultraviolet light. 
     In accordance with another embodiment, the system includes at least one ultrasonic transducer configured to produce an acoustic Bragg grating. 
     In accordance with another embodiment, the photochromic layer has an edge and the source of the additional light includes an infrared light source that emits infrared light into the photochromic layer along the edge. 
     In accordance with another embodiment, the glare is associated with light from an external object, the system includes one or more sensors that are configured to gather information on where the external object is located and the light modulator is further configured reduce the light by selectively darkening the area based at least partly on the information on where the external object is located. 
     In accordance with an embodiment, a vehicle mirror is provided that includes a reflective layer that reflects visible light, a light source that produces light that passes through the reflective layer, and a photochromic layer coupled to the reflective layer that is selectively darkened where exposed to the light from the light source that has passed through the reflective layer. 
     In accordance with another embodiment, the reflective layer includes a Bragg reflector. 
     In accordance with another embodiment, the light source includes an ultraviolet light source and the light from the light source includes ultraviolet light that darkens a local area of the photochromic layer. 
     In accordance with an embodiment, a vehicle window is provided that includes a transparent layer, an array of light-emitting diodes that produces light, and a photochromic layer on the transparent layer that is selectively darkened where exposed to the light from the array of light-emitting diodes. 
     In accordance with another embodiment, the vehicle window includes an infrared light source that is configured to apply infrared light to the photochromic layer to bleach the photochromic layer. 
     In accordance with another embodiment, the vehicle window includes a filter configured to allow visible light to pass and to block ultraviolet light. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20160901
Publication Date: 20210928
Grant Date: 20210928
Priority Date: 20150921
Inventors: CHOI, HYUNGRYUL J.
ZHANG, Arthur Y.
CHEN, CHENG
MYHRE, GRAHAM B.
NORTHCOTT, MALCOLM J.
SIDDIQUI, MATHEEN M.
WEBB, RUSSELL Y.
LAST, MATTHEW E.
Assignee: APPLE INC
CPC Classifications: [{"code": "B60J3/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "B60R16/037", "inventive": true, "first": false, "tree": "[]"}, {"code": "B60J3/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "B60J3/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "B60J3/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "B60R16/037", "inventive": true, "first": false, "tree": "[]"}, {"code": "B60J3/06", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57047280