Abstract:
A system and method of generating perceived white light by laser. The system comprises a laser, a phosphoric substrate, and optionally a diffraction grating. In one embodiment, a blue laser beam from the laser penetrates the phosphoric substrate to create perceived white light in a Gaussian distribution appropriate for emergency lighting. In another embodiment, the blue laser beam is split into multiple beams by the diffraction grating. The multiple beams penetrate the phosphoric substrate to create perceived white light in a Gaussian distribution appropriate for emergency lighting.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    This invention relates generally to systems and methods for perceived white source lighting. More particularly, this invention relates to laser lighting systems for high efficiency white light source generation in emergency settings. 
         [0003]    2. Description of Related Art 
         [0004]    The generation of white light is essential in certain emergency situations when ambient light is not present. Emergency lighting devices must be capable of providing substantially white, long lasting, and appropriately distributed light to meet safety objectives. 
         [0005]    Incandescent lighting is one of the oldest forms of emergency lighting and has a notable disadvantage of power inefficiency, leading to short illumination time when battery power is limited. Also, incandescent lighting is not as bright as some of the more modern light sources. 
         [0006]    Current white lighting devices include apparatuses comprising light emitting diodes (LED&#39;s) and one or more phosphors. Blue light from one or more LED&#39;s penetrate the phosphors to generate perceived white light. Since each LED is capable of providing only a small quantity of light, multiple LED&#39;s must be combined and focused using a plastic lens system built into a solid state unit. The lens system leads to a much narrower Gaussian distribution of light than is desired for emergency situations. These systems have a disadvantage of high power consumption, leading to short operating duration. Longevity is essential, especially in the developing world where power may be turned off for hours. 
         [0007]    Laser diodes are another candidate for generating white light in a similar manner to LED&#39;s, however laser diodes also suffer from poor energy efficiency. Laser diode systems require a lens or reflector system in addition to a yellow phosphorous radiant conversion system, which leads to losses when using a low powered laser diode. Moreover, they pose a safety hazard if a system container is damaged. Current laser diode systems are suitable for high intensity applications such as automobile headlights, however due to efficiency limitations they are not well adapted to provide low level light with a light distribution appropriate for emergency situations. 
         [0008]    Therefore, it is an object of the present invention to provide a system and method for producing high efficiency perceived white light emergency lighting. It is another object of the present invention to provide perceived white light in a bell shaped Gaussian curve appropriate for emergency lighting. 
       SUMMARY OF THE INVENTION 
       [0009]    In one aspect of the system of the present invention, the system comprises a laser diode, a collimator, and a phosphoric substrate. The collimator is coupled to the laser diode. The phosphoric substrate is positioned collinearly with the laser diode to receive a laser beam therefrom. In one embodiment, a diffraction grating is positioned between the collimator and the phosphoric substrate. 
         [0010]    In an exemplary embodiment, the system further comprises an emergency light control adapted to control an output of the laser diode. In another embodiment, the system further comprises a battery charging system configured to provide power to the laser diode. 
         [0011]    In one embodiment of the present invention, the system does not comprise a lens. In another embodiment, the system does not comprise a reflector. 
         [0012]    In one aspect of the method of the present invention, a laser diode is provide with a collimator and directed at a phosphoric substrate. In an exemplary embodiment, a diffraction grating is provided between the collimator and the phosphoric substrate. 
         [0013]    In an exemplary embodiment, an emergency light control adaptor is provided to control output of the laser diode. In another embodiment, a battery charging system is provided to power the laser diode. 
         [0014]    In one embodiment of the present invention, no lens is provided. In another embodiment, no reflector is provided. Not having lenses or reflectors provides an advantage of reduced system losses. Not having lenses or reflectors provides an additional advantage of reduced manufacturing time and expenses. 
         [0015]    As an optional feature of the present invention, the laser diode, collimator, substrate, and diffraction grating are contained inside a housing of a lightbulb. In one aspect, the system further comprises a thermal management system. 
         [0016]    In one embodiment, a distance between the diffraction grating and the substrate is less than 10 microns. In another embodiment, the laser diode and collimator produce an output of at least 55 mw. 
         [0017]    In the method of the present invention, a laser beam from the laser diode and collimator penetrates the phosphoric substrate. In some embodiments, the laser beam is blue and the phosphoric substrate comprises yellow phosphorous. 
         [0018]    An optional step in the method of the present invention comprises positioning the laser, diffraction grating, and substrate inside a housing of a lightbulb. In one aspect, a thermal management system is provided. 
         [0019]    The system and method of the present invention produce perceived white light in a Gaussian distribution. 
         [0020]    The present invention offers the advantages of providing an efficient white light source in a bell shaped Gaussian curve without relying on an elaborate optical system. Further, the present invention allows for thermal management by virtue of allowing laser components to be placed at a great distance from substrate components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic of the laser lighting system according to one embodiment of the present invention. 
           [0022]      FIG. 2  is a side view of the substrate. 
           [0023]      FIG. 3  is a schematic of the laser lighting system according to an alternative embodiment of the present invention. 
           [0024]      FIG. 4  is an illustration of the radiant output of the substrate according to the embodiment of  FIG. 1 . 
           [0025]      FIG. 5  is an illustration of the radiant output of the substrate according to the embodiment of  FIG. 3 . 
           [0026]      FIG. 6  is an image of perceived white light output according to an embodiment of the present invention. 
           [0027]      FIG. 7  is a posterized image of perceived white light output according to the embodiment of  FIG. 6 . 
           [0028]      FIG. 8  is an image of perceived white light output according to the embodiment of  FIG. 1 . 
           [0029]      FIG. 9  is a posterized image of perceived white light output according to the embodiment of  FIG. 1 . 
           [0030]      FIG. 10  is an image of perceived white light output according to the embodiment of  FIG. 3 . 
           [0031]      FIG. 11  is a posterized image of perceived white light output according to the embodiment of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Embodiments of the present invention provide systems and methods employing a laser and a substrate to generate perceived white light. In particular, a laser beam penetrates a phosphorous layer of the substrate to generate the perceived white light. In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of structures. Those skilled in the art will also recognize additional modifications, applications, and embodiments are within the scope thereof, as are additional fields in which the invention may provide utility. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to limit the scope of the invention. 
         [0033]      FIG. 1  illustrates one embodiment of the present invention. A laser  1  is positioned at a distance from a substrate  2 . A laser beam B is emitted from the laser  1 . The laser beam B penetrates the substrate  2 , which comprises a yellow phosphate. Perceived white light P is emitted from the substrate  2 . 
         [0034]    The laser beam B is highly collimated coherent light. When it impacts the substrate  2 , the laser beam is refracted into spatial light as if from a common incandescent light source producing white light. In one embodiment, the laser beam B impacts the substrate  2  at a 90 degree angle. In some embodiments, the system has an angle of illumination of 180 degrees. 
         [0035]    Referring to  FIG. 2 , the substrate  2  is shown in more detail. The substrate  2  comprises clear plastic  21 . In one embodiment, the clear plastic layer  21  as a depth of  1  mm. However, it will be appreciated by those skilled in the art that there are many suitable thicknesses of the plastic layer  21 . The substrate  2  further comprises a yellow phosphorous layer  22 . Blue light of the laser beam B penetrating the yellow phosphorous layer  22  will cause perceived white light. It will be appreciated by those skilled in the art that the yellow phosphorous layer  22  can be positioned on either side of the clear plastic  21 . Testing has revealed that performance is unchanged regardless of which side the yellow phosphorous layer  22  is positioned with respect to the laser. An inwardly facing yellow phosphorous layer  22  is preferred because the clear plastic layer  21  protects the yellow phosphorous layer  22  from the environment. 
         [0036]    In an alternative embodiment, a diffraction grating  3  is introduced into the system, as shown in  FIG. 3 . The diffraction grating  3  is positioned very close to the substrate  2 . In some embodiments, the diffraction grating  3  is less than 10 microns from the substrate  2 . A laser beam B from the laser  1  is split into multiple beams M by the diffraction grating  3 . The multiple beams M penetrate the substrate  2  at different locations on the substrate. Perceived white light P is emitted from the substrate. 
         [0037]    The embodiment of  FIG. 3  has a notable advantage of reducing or preventing saturation. The substrate  2  does not have infinite radiant output capacity, and will therefore become saturated if a radiant flux of laser light becomes sufficiently high within a given area of substrate. Beyond a certain intensity of blue laser light, perceived white light will no longer increase, because yellow light output intensity from the substrate  2  will no longer increase. This phenomena is illustrated in  FIG. 4 . A laser beam B impacts the substrate  2  (not shown), and the substrate  2  will emit light with an intensity (I) plane C, which is a function of x and y position on the substrate  2 . There is a saturation intensity S, at which no additional white light will be produced with additional laser beam B intensity. In the example of  FIG. 1 , the substrate  2  is saturated. 
         [0038]    Saturation may be avoided by implementing the embodiment of  FIG. 3 . As shown in  FIG. 5 , a laser beam B is split into multiple beams M when it passes through a diffraction grating  3 . The multiple beams M impacts the substrate  2  (not shown), and the substrate  2  will emit light with an intensity (I) plane C, which is a function of x and y position on the substrate  2 . The saturation intensity S is also shown in  FIG. 5 . In this example, saturation is not reached because the multiple beams M are distributed over the substrate  2 . Therefore, the radiant flux in any given area will not become sufficiently high to cause saturation. 
         [0039]    Embodiments of the present invention including a collimator are preferred based on experimental data. Referring now to  FIG. 6 , an image of perceived white light output is shown for an embodiment having only a laser diode and a substrate.  FIG. 7  shows a posterized image of the same. The distribution of light shown in  FIGS. 6 and 7  is less preferred because it is fanned out and is more appropriate for surface lighting. 
         [0040]    Referring now to  FIG. 8 , an image of perceived white light output is shown for an embodiment having a laser beam and a substrate.  FIG. 9  shows a posterized image of the same. The distribution of light shown in  FIGS. 8 and 9  is more preferred than that of the embodiment having only a laser diode and substrate because it has a narrower distribution. However, the distribution may be too narrow for certain emergency lighting situations. 
         [0041]    Referring now to  FIG. 10 , an image of perceived white light output is shown for an embodiment with multiple laser beams and a substrate. The multiple laser beams were created by a diffraction grating.  FIG. 11  shows a posterized image of the same. The distribution of light shown in  FIGS. 10 and 11  is most preferred because it has an ideal distribution for emergency lighting situations. 
         [0042]    Experiments were conducted to evaluate the performance of various system configurations. A lux meter was placed at zero distance from outputs sources of perceived white light in order to capture all forward light output. Although data is presented in lux/mw as measured by the lux meter, it is not true lux/mw because the lux meter was placed at zero distance from the output sources. 
         [0043]    The testing revealed that under certain conditions, if a single laser beam is used, the output of white light is 3561 ux/mw. If under the same conditions, a diffraction grating (DG) is used to produce multiple lasers beams, the output of white light is 5201 ux/mw. 
         [0044]    The diffraction grating itself reduces the laser output from 50 mw to 32 mw, meaning only 64% of the laser power is delivered to the yellow phosphorus. However, it was observed that the efficiency of the system is higher when the diffraction grating is used, which is an unexpected result. Supporting data is tabulated below. 
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Laser Diode Only Power 
                 Lux output 
               
               
                   
               
             
             
               
                 60 mw 
                 21000 lux 350 lux/mw (tested) 
               
               
                 50 mw 
                 17500 lux 350 lux/mw (predicted) 
               
               
                 44 mw 
                 15200 Lux 345 lux/mw (tested) 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Single Laser Beam Power 
                 Lux output 
               
               
                   
               
             
             
               
                 50 mw 
                 19020 lux 380 lux/mw (tested) 
               
               
                 32 mw 
                 12160 lux 380 lux/mw (predicted) 
               
               
                 35 mw 
                 13000 lux 371 lux/mw (tested) 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Multiple 
                   
               
               
                 Laser 
               
               
                 Beam Power 
                 Lux output 
               
               
                   
               
             
             
               
                 32 mw 
                 16660 lux 520 lux/mw (tested), 64% efficient DG used 
               
               
                 50 mw 
                 26000 lux 520 lux/mw (predicted), 100% efficient DG used 
               
               
                 45 mw 
                 23400 lux 520 lux/mw (predicted), 90% efficient DG used 
               
               
                 23 mw 
                 12300 lux 534 lux/mw (tested), 64% efficient DG used 
               
               
                   
               
             
          
         
       
     
         [0045]    While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention.