Patent Publication Number: US-2022221754-A1

Title: Photochromic dye and liquid crystal optical element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. non-provisional application Ser. No. 16/854,181 filed Apr. 21, 2020, which claims priority to U.S. provisional Application No. 62/911,211 filed Oct. 5, 2019. U.S. non-provisional application Ser. No. 16/854,181 and U.S. provisional application 62/911,211 are incorporated by reference herein. 
    
    
     BACKGROUND INFORMATION 
     Photochromic lenses are commonly used in both prescription glasses and non-prescription sunglasses. In some photochromic lenses, photochromic molecules included in the lenses reduce transmission of incident light through the lens (darkening) in response to ultraviolet light, for example. Yet, in certain thermal environments, non-uniform darkening of the photochromic lenses may become readily apparent due to a changing transparency of photochromic molecules with respect to temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  illustrates glasses that include photochromic lenses. 
         FIGS. 2A-2C  illustrate an example optical element including a solution of liquid crystals co-mingled with oblong photochromic dye molecules, in accordance with an embodiment of the disclosure. 
         FIGS. 3A-3C  illustrate an alignment of liquid crystals at a second temperature and a transmission characteristic of oblong photochromic dye molecules at the second temperature, in accordance with an embodiment of the disclosure. 
         FIGS. 4A-4C  illustrate an alignment of liquid crystals at a third temperature and a transmission characteristic of oblong photochromic dye molecules at the third temperature, in accordance with an embodiment of the disclosure. 
         FIG. 5  illustrates a head mounted device that includes photochromic optical elements, in accordance with an embodiment of the disclosure. 
         FIG. 6  illustrates a head mounted display (HMD) that includes photochromic optical elements, in accordance with an embodiment of the disclosure. 
         FIG. 7  illustrates a top view of a photochromic optical element that includes a waveguide, in accordance with an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a photochromic optical element are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     In some embodiments of the disclosure, “near-eye” may be defined as including an optical element that is configured to be placed within 35 mm of an eye of a user while a near-eye optical device such as a head mounted device or head mounted display (HMD) is being utilized. 
     In aspects of this disclosure, visible light may be defined as having a wavelength range of approximately 380 nm-700 nm. Non-visible light may be defined as light having wavelengths that are outside the visible light range, such as ultraviolet light and infrared light. Infrared light having a wavelength range of approximately 700 nm-1 mm includes near-infrared light. In aspects of this disclosure, near-infrared light may be defined as having a wavelength range of approximately 700 nm-1.4 μm. 
     In aspects of this disclosure, the term “transparent” may be defined as having greater than 90% transmission of light. In some aspects, the term “transparent” may be defined as a material having greater than 90% transmission of visible light. 
     Embodiments of this disclosure may improve photochromic absorption consistency when an optical element has a thermal gradient. Absorption dyes (photochromic molecules) used in photochromic elements may lose absorption when they get warmer. A lens in a head mounted display (HMD), for example, often gets hotter around the edge and so the absorption around the edge of a photochromic lens is less than the colder middle of the lens. To address this, oblong photochromic dye molecules may be co-mingled with liquid crystals in a solution. Some liquid crystals become disordered in alignment in response to heat. Oblong photochromic dye molecules may tend to align with the disordered liquid crystals which may increase the exposed cross-section of the oblong photochromic molecules that is exposed to incoming light (increasing the absorption). An optical element may include a photochromic cell where oblong photochromic dye molecules are co-mingled with liquid crystals. In embodiments of the disclosure, the disordered alignment characteristics of the liquid crystal may offset or partially offset the decreased dye absorption caused by heat by increasing the exposed cross-section of the oblong photochromic dye molecules that align with the liquid crystals. Consequently, the optical element (e.g. a photochromic lens) may have a uniform or substantially uniform transmission profile across the optical element even when there is a thermal gradient across the optical element. 
     In one embodiment, the photochromic optical element is passive and relies on the disordered nature of liquid crystal in response to temperature paired with the oblong photochromic dye molecules to generate the more uniform transmission through the optical element. 
     In an embodiment, one or more active shutters are utilized to actively drive the optical element to minimum absorption orientation or maximum absorption orientation to control the transmission of light. The active shutter embodiment may include one or more photochromic cells that includes oblong photochromic dye molecules co-mingled with liquid crystals. The photochromic cell may be disposed between two electrode layers that may be transparent to visible light (e.g. indium tin oxide). The electrode layers may be driven digitally (OFF or ON) or may be driven to provide more granular grey-scale control in order to more finely control the transmission through the optical element. Actively driving the one or more active shutters may provide more uniform transmission control through the optical element regardless of a temperature gradient across the optical element. These and other embodiments are described in more detail in connection with  FIGS. 1-7 . 
       FIG. 1  illustrates glasses  199  that include photochromic lenses  172 A and  172 B (referred to collectively as lenses  172 ). Glasses  199  include arms  161 A and  161 B coupled to a frame  164 . Photochromic optical elements  172 A and  172 B are included in frame  164 .  FIG. 1  shows that photochromic optical elements  172  are more transmissive on the outside of the photochromic elements  172  when the outside of the photochromic optical elements have a higher temperature than the middle (darkest) part of photochromic optical elements  172 . If glasses  199  are a head mounted device or “smart glasses,” heat dissipating from batteries, power supplies, processors, or otherwise may contribute to a thermal gradient across photochromic optical elements  172 . In some contexts, the outside edge of photochromic optical elements  172  may be 10° C. warmer (or more) than a middle of photochromic optical elements  172  that translates into a thermal gradient that increases in temperature as a position of the photochromic optical element  172  goes toward an outside boundary (edge) of the photochromic optical element that is proximate to (or contacting) the frame  164 . 
       FIGS. 2A-2C  illustrate an example optical element  200  including a solution of liquid crystals co-mingled with oblong photochromic dye molecules, in accordance with aspects of the disclosure.  FIG. 2A  illustrates a top view of a portion of an optical element  200  that includes a first boundary layer  220 , a second boundary layer  240 , and a solution  230  disposed between the first boundary layer  220  and the second boundary layer  240 . When optical element  200  is fabricated for use with glasses, first boundary layer  220  may be referred to as an eyeward transparent boundary layer and second boundary layer  240  may be referred to as a scene-side transparent boundary layer. Optical element  200  may be a near-eye optical element. Solution  230  includes a plurality of liquid crystals  235  co-mingled with oblong photochromic dye molecules  233 .  FIGS. 2A-4C  depict liquid crystals  235  and oblong photochromic dye molecules  233  at a function level and may not necessarily be drawn to scale. Furthermore, the concentration of liquid crystals  235  and oblong photochromic dye molecules  233  may vary from the illustration, in actual implementation. 
       FIG. 2A  illustrates an alignment of liquid crystals  235  at a first temperature and a transmission characteristic of oblong photochromic dye molecules  233  at that same first temperature. The first temperature may be 20° C., for example. The first temperature may be 25° C., in some embodiments. The first temperature may be 30° C. or more, in some embodiments. 
     At the first temperature, the long axis  236 A of the liquid crystals  235  are self-aligned approximately normal to eyeward transparent boundary layer  220  and scene-side transparent boundary layer  240 . Liquid crystals  235  may be rod-shaped liquid crystals to facilitate self-alignment of long axis  236 A normal to eyeward transparent boundary layer  220  and scene-side transparent boundary layer  240 . Oblong photochromic dye molecules  233  are configured to align with the liquid crystals  235  so that a long axis  234 A of the oblong photochromic dye molecules  233  will generally align with the long axis  236 A of liquid crystals  235  that are proximate to a particular oblong photochromic dye molecule  233 . In the particular illustration of  FIG. 2A , long axis  236 A of liquid crystal  235 A is positioned approximately in parallel with the long axis  234 A of oblong photochromic dye molecule  233 A, for example. 
     In  FIG. 2A , incoming light  299 A is incident upon scene-side transparent layer  240  approximately normal to the scene-side transparent layer  240 . As incoming light  299 A propagates through solution  230 , a portion of incoming light  299 A is absorbed by oblong photochromic dye molecules  233 . A remaining portion of incoming light  299 A that is not absorbed by oblong photochromic dye molecules  233  exits optical element  200  as remaining light  298 A. In  FIGS. 2A-2C , oblong photochromic dye molecule  233  are illustrated having a solid black fill to represent a high-absorption characteristics of oblong photochromic dye molecules  233  at the first temperature. Notably, the solid black fill may represent the relative aggregate transmission characteristics of oblong photochromic dye molecules  233  in  FIGS. 2A-2C  as a whole since individual molecules  233  may be either in a fully absorbing or fully clear (transmissive) state, in some implementations. 
       FIG. 2B  illustrates a front view of a portion of optical element  200  at the first temperature.  FIG. 2B  depicts incoming light  299 A going into-the-page encountering scene-side transparent boundary layer  240  approximately normal to scene-side transparent boundary layer  240  and propagating through solution  230  and eyeward transparent boundary layer  220 . Notably, since liquid crystals  235  are aligned approximately normal to scene-side transparent boundary layer  240 , a cross-section of liquid crystals  235  and a cross-section of oblong photochromic dye molecules  233  (aligned with the liquid crystals  235 ) approach the smallest possible cross-section of the liquid crystals  235  and approach the smallest possible cross-section of the oblong photochromic dye molecules  233  exposed to incoming light  299 A. Therefore, although the oblong photochromic dye molecules  233  have high-absorption at the first temperature, the cross-section of the oblong photochromic dye molecules  233  is relatively small. 
       FIG. 2C  illustrates a zoomed-in view of an example liquid crystal  235 A and an example oblong photochromic dye molecule  233 A that illustrate the small cross-section of liquid crystals  235  and the corresponding small cross-section  237  of oblong photochromic dye molecule  233 A facing incoming light  299 A to absorb incoming light  299 A.  FIG. 2C  shows that the long axis  236 A of example liquid crystal  235 A is into-the-page. As discussed above, a concentration of oblong photochromic dye molecules  233  may be different (e.g. much more concentrated) than illustrated. 
       FIG. 3A  illustrates an alignment of liquid crystals  235  at a second temperature and a transmission characteristic of oblong photochromic dye molecules  233  at the second temperature. The second temperature is warmer than the first temperature. The second temperature may be 5° C. warmer than the first temperature, for example. 
     At the second temperature, the long axis  236 B of the liquid crystals  235  are no longer self-aligned to be oriented normal to eyeward transparent boundary layer  220  and scene-side transparent boundary layer  240 . Rather, at the second temperature in  FIG. 3A , liquid crystals  235  are slightly disordered due to the increased temperature of the second temperature. Since the liquid crystals  235  are slightly disordered, the long axis  236  of the liquid crystals  235  are no longer substantially aligned and therefore the long axis  234 B of the oblong photochromic dye molecules  233  are no longer oriented normal to scene-side transparent boundary layer  240  and eyeward transparent boundary layer  220 . 
     In  FIG. 3A , incoming light  299 B is incident upon scene-side transparent layer  240  approximately normal to the scene-side transparent layer  240 . As incoming light  299 B propagates through solution  230 , a portion of incoming light  299 B is absorbed by oblong photochromic dye molecules  233 . A remaining portion of incoming light  299 B that is not absorbed by oblong photochromic dye molecules  233  exits optical element  200  as remaining light  298 B. In  FIGS. 3A-3C , oblong photochromic dye molecule  233  are illustrated having a speckled fill to represent a mid-absorption characteristic of oblong photochromic dye molecules  233  at the second temperature. Here again, the speckled fill may represent the relative aggregate transmission characteristics of oblong photochromic dye molecules  233  in  FIGS. 3A-3C  as a whole since individual molecules  233  may be either in a fully absorbing or fully clear (transmissive) state, in some implementations. 
       FIG. 3B  illustrates a front view of a portion of optical element  200  at the second temperature.  FIG. 3B  depicts incoming light  299 B going into-the-page encountering scene-side transparent boundary layer  240  approximately normal to scene-side transparent boundary layer  240  and propagating through solution  230  and eyeward transparent boundary layer  220 . Since liquid crystals  235  are slightly disordered at the second temperature, a greater cross-section of the oblong photochromic dye molecules  233  (also slightly disordered due to their aligning with the slightly disordered liquid crystals  235 ) faces incoming light  299 B and therefore incoming light  299 B encounters a larger cross-section of oblong photochromic dye molecules  233  as incoming light  299 B propagates through solution  230 . However, the larger cross-section of oblong photochromic dye molecules  233  that faces incoming light  299 B at the second temperature (attributed to the slight disorder of liquid crystals  235  at the second temperature) is offset (or balanced) by the reduced absorption of oblong photochromic dye molecules  233 B. Consequently, the intensity of remaining light  298 B may be the same as the intensity of remaining light  298 A. 
       FIG. 3C  illustrates a zoomed-in view of an example liquid crystal  235 B and an example oblong photochromic dye molecule  233 B that illustrate the greater cross-section of liquid crystals  235  and the corresponding medium cross-section  237 B of oblong photochromic dye molecule  233 B facing incoming light  299 B to absorb incoming light  299 B. 
       FIG. 4A  illustrates an alignment of liquid crystals  235  at a third temperature and a transmission characteristic of oblong photochromic dye molecules  233  at the third temperature. The third temperature is warmer than the second temperature. The third temperature may be 5° C. warmer than the second temperature, for example. 
     At the third temperature, the long axis  236 C of the liquid crystals  235 C are not self-aligned to be oriented normal to eyeward transparent boundary layer  220  and scene-side transparent boundary layer  240 . Rather, at the third temperature in  FIG. 4A , liquid crystals  235  are disordered due to the increased temperature of the third temperature. Since the liquid crystals  235  are disordered, the long axis of the liquid crystals  235  are not aligned and therefore the long axis  234 C of the oblong photochromic dye molecules  233  are not normal to scene-side transparent boundary layer  240  and eyeward transparent boundary layer  220 . 
     In  FIG. 4A , incoming light  299 C is incident upon scene-side transparent layer  240  approximately normal to the scene-side transparent layer  240 . As incoming light  299 C propagates through solution  230 , a portion of incoming light  299 C is absorbed by oblong photochromic dye molecules  233 . A remaining portion of incoming light  299 C that is not absorbed by oblong photochromic dye molecules  233  exits optical element  200  as remaining light  298 C. In  FIG. 4A , oblong photochromic dye molecule  233  are illustrated having a sparse fill to represent a low-absorption characteristic of oblong photochromic dye molecules  233  at the third temperature. As noted in connection with  FIGS. 2A-3C , the sparse fill may represent the relative aggregate transmission characteristics of oblong photochromic dye molecules  233  in  FIGS. 4A-4C  as a whole since individual molecules  233  may be either in a fully absorbing or fully clear (transmissive) state, in some implementations. 
       FIG. 4B  illustrates a front view of a portion of optical element  200  at the third temperature.  FIG. 4B  depicts incoming light  299 C going into-the-page encountering scene-side transparent boundary layer  240  approximately normal to scene-side transparent boundary layer  240  and propagating through solution  230  and eyeward transparent boundary layer  220 . Since liquid crystals  235  are disordered at the third temperature, a greater cross-section of the oblong photochromic dye molecules  233  (also disordered due to their aligning with the disordered liquid crystals  235 ) faces incoming light  299 C and therefore incoming light  299 C encounters a very large cross-section of oblong photochromic dye molecules  233  as incoming light  299 C propagates through solution  230 . However, the very large cross-section of oblong photochromic dye molecules  233  that face incoming light  299 C at the third temperature (attributed to the disorder of liquid crystals  235  at the third temperature) is offset (or balanced) by the reduced absorption of oblong photochromic dye molecules  233  at the third temperature. Consequently, the intensity of remaining light  298 C may be the same as the intensity of remaining light  298 B and remaining light  298 A. 
       FIG. 4C  illustrates a zoomed-in view of an example liquid crystal  235 C and an example oblong photochromic dye molecule  233 C that illustrate the very large cross-section of liquid crystals  235 C and the corresponding large cross-section  237 C of oblong photochromic dye molecule  233 C facing incoming light  299 C to absorb incoming light  299 C. 
       FIG. 5  illustrates a head mounted device  500  that includes photochromic optical elements  522 A and  522 B (referred to collectively as optical elements  522 ) that include the structure of optical element  200 , in accordance with aspects of the disclosure. Head mounted device  500  may be considered to be “electronic glasses” or “smart glasses,” in some contexts. Head mounted device  500  includes electronic such as processing logic  545  and element  547 . Element  547  may be a camera, in some embodiments. Head mounted device  500  may also include additional electronic elements (not illustrated) such as a battery, network communication chipsets (e.g. IEEE 802.11x wireless interface), power converters (e.g. switching power supplies), and otherwise. The electronics included in head mounted device  500  may be disposed in arms  511 A and  511 B and frame  514  that is coupled to arms  511 A and  511 B. 
     The heat dissipated by these electronics may be conducted into photochromic optical elements  522 A and  522 B that increases the temperature of photochromic optical elements  522  that may otherwise have a temperature that is similar to the ambient air temperature. Consequently, a temperature gradient may exist across photochromic optical elements  522 . In some embodiments, this temperature gradient increases in temperature as a position of the photochromic optical element goes toward an outside boundary (edge) of the photochromic optical element that is proximate to (or contacting) the frame  164 .  FIG. 5  illustrates a first coordinate  541 , a second coordinate  542 , and a third coordinate  543 . First coordinate  541  is approximately in a middle or center of photochromic optical element  522 B and third coordinate  543  is very close to an outside edge of the photochromic optical element  522 B. Second coordinate  542  is disposed approximately midway between first coordinate  541  and third coordinate  543 . While not specifically illustrated, those skilled in the art appreciate that similar thermal gradients may exist across photochromic optical element  522 A. 
     First coordinate  541  may be at the first temperature (e.g. 25° C.) and optical element  522 B at first coordinate  541  may have an associated orientation of liquid crystals  235  and corresponding orientation of oblong photochromic dye molecules  233  as illustrated in  FIGS. 2A-2C . Third coordinate  543  may be at the third temperature (e.g. 35° C.) and optical element  522 B at third coordinate  543  may have an associated orientation of liquid crystals  235  and corresponding orientation of oblong photochromic dye molecules  233  as illustrated in  FIGS. 4A-4C . Second coordinate  542  may be at the second temperature (e.g. 30° C.) and optical element  522 B at second coordinate  542 B may have an associated orientation of liquid crystals  235  and corresponding orientation of oblong photochromic dye molecules  233  illustrated in  FIGS. 3A-3C . Yet, even as coordinates  541 ,  542 , and  543  experience different temperatures, the transmission of incoming light  599  is approximately equal across photochromic optical element  522 B, just as the intensities of remaining light  298 A,  298 B, and  298 C may be the same through optical element  200  over different temperature ranges. Hence, photochromic optical elements  522 A and  522 B are illustrated with a substantially uniform darkening because the liquid crystals  235  are configured to become increasingly disordered in response to increased temperature and the oblong photochromic dye molecules  233  are configured to align with the liquid crystals  235  and increase the cross section of the oblong photochromic dye molecules with respect to incoming light  599  (as the liquid crystals  235  increase in disorder). 
     The oblong photochromic dye molecules  233  may be matched to the liquid crystals  235  to offset a decrease in absorption of the oblong photochromic dye molecules  233  in response to increased temperature such that a transmission of the incoming light  599  is approximately equal across photochromic optical element  522 B when a temperature gradient exists across the photochromic optical element. In other words, the remaining light  598  (portion of the incoming light  599  that is not absorbed or otherwise scattered) may have approximately the same intensity regardless of the coordinate of incidence of the incoming light  599  upon photochromic optical element  522 B. A first refractive index of liquid crystals  235  may be substantially equal to a second refractive index of the oblong photochromic dye molecules  233 . 
       FIG. 6  illustrates a head mounted display (HMD)  600  that includes photochromic optical elements  622 , in accordance with aspects of the disclosure. In  FIG. 6 , photochromic optical element  622 A include a waveguide  650 A to direct image light generated by display  660 A to an eye of a user. Photochromic optical element  622 B may also include a waveguide  650 B to direct image light generated by display  660 B to an eye of a user. Therefore, in some embodiments, photochromic optical elements include a waveguide  650  to present images to an eye of a wearer of HMD  600 . The waveguide  650  may be disposed on an eyeward side of eyeward transparent boundary layer  220  of the photochromic optical element  200 . HMD  600  may include alternative display optical elements (not illustrated) to facilitate display architectures that do not necessarily use a waveguide to present images to an eye of a wearer of HMD  600 . For example, HMD  600  may utilize a holographic display to present images to an eye of a wearer of HMD  600 . 
       FIG. 7  illustrates a top view of photochromic optical element  700  that includes a waveguide  750 , in accordance with aspects of the disclosure. Waveguide  750  is disposed on an eyeward side of transparent layer  720 . Waveguide  750  directs image light  751  in an eyeward direction to present images to an eye of a wearer of an HMD (e.g. HMD  600 ). In  FIG. 7 , photochromic optical element  700  includes a first transparent conductive layer  720  and a second transparent conductive layer  740 . First transparent conductive layer  720  and second transparent conductive layer  740  may be indium tin oxide (ITO), for example. 
     Processing logic  770  may be configured to drive a voltage V c    773  across first transparent conductive layer  720  and second transparent conductive layer  740  to control an alignment of the liquid crystals  235  with respect to first transparent conductive layer  720  and second transparent conductive layer  740 . Processing logic  770  may include appropriate transistors to facilitate driving voltage V c    773  across first transparent conductive layer  720  and second transparent conductive layer  740 . Processing logic  770  may be configured to drive a digital voltage V c    773  (e.g. 0 VDC or 3.3 VDC) across first transparent conductive layer  720  and second transparent conductive layer  740 , where the digital-high voltage functions to align the long axes of liquid crystals  235  normal to first transparent conductive layer  720  and second transparent conductive layer  740  and the digital-low voltage allows the liquid crystals  235  to become disordered. 
     In some embodiments, processing logic  770  may drive a grey-level analog voltage V c    773  (e.g. variable voltage between 0 VDC and 3.3 VDC) across first transparent conductive layer  720  and second transparent conductive layer  740  to facilitate more granular control over the alignment of liquid crystals  235 . In this embodiment, the higher the voltage V c    773 , the more the long axes of the liquid crystals would be aligned normal to first transparent conductive layer  720  and second transparent conductive layer  740 , as illustrated in  FIG. 7 . In contrast, the lower the voltage V c    773 , the more disordered the liquid crystals  235  become. 
     Regardless of whether processing logic  770  drives a digital or grey-level voltage V c    773  across first transparent conductive layer  720  and second transparent conductive layer  740 , processing logic  770  may drive voltage V c    773  in response to a light signal received from sensor  780 . Sensor  780  may be configured to receive and measure ambient light  783  from an external environment of the optical element  700 . Processing logic  770  is configured to receive the light signal from sensor  780 . In one embodiment, sensor  780  is a photodiode generating an electrical current corresponding to an intensity of ambient light  783 . In some embodiments, sensor  780  includes a complementary metal-oxide semiconductor (CMOS) image sensor generating an image and processing logic  770  derives an intensity of ambient light  783  from pixel values of the image. 
     Whether processing logic  770  drives a digital or grey-level voltage V c    773  across first transparent conductive layer  720  and second transparent conductive layer  740 , processing logic  770  is configured to control the alignment of the liquid crystals  235  and thus the transmission of incoming light  799  by way of oblong photochromic dye molecules  233  (and corresponding cross-sections facing incoming light  799 ) aligning with liquid crystals  235 . The remaining light  798  (the portion of incoming light  799  that is not absorbed by oblong photochromic dye molecules  233 ) propagates through waveguide  750  and continues toward an eye of a wearer of a head mounted device. 
     In some embodiments, processing logic  770  may have a default state of driving 0 VDC as voltage V c    773  and allowing solution  230  to passively control the transmission of incoming light  799  with respect to heat, as described in association with  FIGS. 2A-4C . Processing logic  770  may change to an active state that drives a voltage V c    773  in order to align or partially align liquid crystals  235 . In one context, a wearer of a head mounted device that includes optical element  700  is in an outdoor environment in bright sunlight that activates oblong photochromic dye molecules  233  into a darkened (absorbing) state. Then the wearer of the head mounted device changes to an indoor environment without bright sunlight. In this scenario, optical element  700  may remain darkened or partially darkened for several seconds or even minutes. However, processing logic  770  may drive a digital-high voltage as voltage V c    773  to align liquid crystals  235  and consequently minimize or greatly reduce the cross-section of oblong photochromic dye molecules  233  that would absorb incoming light  799 . In this way, the active state of processing logic  770  reduces the time that optical element  700  remains darkened, upon a user entering an indoor environment where the darkening may no longer be needed. Processing logic  770  may determine an environment switch from an outdoor environment to an indoor environment based on a sudden drop of intensity of a light signal received from sensor  780 , for example. 
     Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers. 
     The term “processing logic” (e.g.  545  or  770 ) in this disclosure may include one or more processors, microprocessors, multi-core processors, Application-specific integrated circuits (ASIC), and/or Field Programmable Gate Arrays (FPGAs) to execute operations disclosed herein. In some embodiments, memories (not illustrated) are integrated into the processing logic to store instructions to execute operations and/or store data. Processing logic may also include analog or digital circuitry to perform the operations in accordance with embodiments of the disclosure. 
     A “memory” or “memories” described in this disclosure may include one or more volatile or non-volatile memory architectures. The “memory” or “memories” may be removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Example memory technologies may include RAM, ROM, EEPROM, flash memory, CD-ROM, digital versatile disks (DVD), high-definition multimedia/data storage disks, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device. 
     A computing device may include a desktop computer, a laptop computer, a tablet, a phablet, a smartphone, a feature phone, a server computer, or otherwise. A server computer may be located remotely in a data center or be stored locally. 
     The processes explained above are described in terms of computer software and hardware. The techniques described may constitute machine-executable instructions embodied within a tangible or non-transitory machine (e.g., computer) readable storage medium, that when executed by a machine will cause the machine to perform the operations described. Additionally, the processes may be embodied within hardware, such as an application specific integrated circuit (“ASIC”) or otherwise. 
     A tangible non-transitory machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable/non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.). 
     The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.