Abstract:
A hair removal device utilizes a system for sensing the presence and color of skin. The system includes a skin color sensor assembly and a capacitive sensor assembly disposed in a housing. The skin color sensor assembly includes a light pipe communicating with a color sensor aperture of the housing and having one or more notches defining receiving and emitting light propagation regions, a color sensor and one or more light emitting diodes, and a holder having at least one standoff mated to the notches thereby directing light emitted by the light emitting diodes through the light pipe for reflection of an external surface and receipt by the sensor for detection of surface color. The capacitive sensor assembly includes a plurality of copper elements in proximity to a device aperture and contacting an interior surface of the housing and for detection of an object in contact with the copper elements.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Reference is hereby made to the following co-pending U.S. application dealing with related subject matter and assigned to the assignee of the present invention: “Single-Emitter Diode Based Light Homogenizing Apparatus And A Hair Removal Device Employing The Same,” U.S. Ser. No. 12/976,466, filed Dec. 22, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Generally, the field of the present invention relates to sensor systems. Specifically, the present invention relates to skin color and capacitive sensor systems for devices including hand-held consumer devices and assemblies thereof. 
         [0004]    2. Background Art 
         [0005]    Several devices and methods are presently used for the removal of hair on a person&#39;s body including applying hot wax to a target area and quickly removing the wax after the wax has cooled, shaving the target area with a razor, applying chemical depilatories to a target area, and applying laser radiation to a targeted area. There are significant advantages to the laser methods over the others with respect to the length of time it takes hair to grow back, ease of the process, etc. However, available laser hair removal devices tend to be far too bulky, unwieldy, and expensive for easy in-home use. 
         [0006]    Many laser-based hair removal devices use bars of laser diodes to generate the light for the device. This typically requires the device to be capable of generating a large current to power the bars. Power supplies capable of producing such currents tend to be large and more expensive than power supplies producing less current. Additionally, larger currents produce more heat which can become a potential hazard if not handled effectively. If the efficiency of the device suffers at any point between the power supply and the targeted treatment area, even more power will be required to make the device function in a particular range. This also has the tendency to produce more heat, further complicating heat dissipation. Resolving heat dissipation can lead to additional or larger components which further detract from the ergonomics of the device and again prevent the useful application of laser removal methods for home use. Also, for safe use, it is important to understand the attributes of the targeted surface such as the type of skin or the presence of skin being targeted as well as to provide safe and secure use of the device. Accordingly, there is a need for a device that incorporates many of the aforementioned advantages and dispenses with the drawbacks. 
       SUMMARY OF THE INVENTION 
       [0007]    The exemplary embodiment of a single-emitter diode based hair removal device, as disclosed herein, has several aspects which are designed to satisfy the aforementioned needs. One aspect relates to a light homogenizing apparatus that uses single-emitter laser diodes disposed adjacent to and capable of emitting into a highly transmissive light guide that refractively adjusts entering beams and homogenizes them so as to produce an output beam exiting the light guide that is substantially uniform in optical intensity across one or both dimensions generally transverse to propagation. The single-emitter diodes may be chosen so that each solid state diode emits at a selected wavelength or wavelength distribution. This allows the spectral power distribution of the final laser beam to be selected or varied for different applications. By comparison, in the current laser hair removal industry, beams tend to be monochromatically limited. Moreover, the use of a set of single-emitter diodes requires less power than a standard laser diode bar. Consequently, single-emitter diodes can be more efficient at generating light since less waste heat is generated, and when they are used in conjunction with laser hair removal the reduction in waste heat can allow for safer and smaller device configurations. Lower waste heat can result in a lower operating temperature which can allow more repeat usage of the device and a longer mean-time between failures as well. Thus, the use of one or more single-emitter diodes allows the system to remain smaller and safer, but also more rugged, reliable, and robust. 
         [0008]    The laser light emitted from the diodes is coupled into a light guide made from a material with a high refractive index. The light guide is shaped to achieve total internal reflection of the laser light along at least one dimension and also minimizes the divergence angle of the light at the exit end of the light pipe. A low divergence angle of the light exiting the light pipe allows a greater amount of light to be directed at the target area rather than being wasted by being directed in an unproductive direction. It also reduces the need for additional expensive optics. The opposite walls of the light guide are tapered or expanded respectively, such that the entrance aperture of the light pipe is a rectangle and the exit aperture is a narrower square. This two-sided tapering reduces power loss by lowering the divergence angle of the exiting light, while shaping the light into an approximately uniform beam for use. 
         [0009]    An optical diffuser is disposed after the light guide that includes an array or arrays of optical lenses, making the efficiency of light transmission through the diffuser very high. The diffuser spreads the power of the incoming light evenly over the area occupied by the exiting light, so that the fluence over the targeted area is more even and consistent but also causes the light to diverge widely to make the emitted beam eye-safe. While the aforementioned features are directed to claims in a co-pending application, cross-referenced above, the construction and function are illustrated and described herein for facilitating a complete and thorough understanding of the features of the system and claims of the present application. 
         [0010]    The present invention relates to another feature of the hair removal device, such being the unique arrangement of sensors that detect the presence and color of a target surface in order to ensure safe application of the device. The skin presence sensor is situated in proximity to a window on the housing of the device and has a circuit that senses the capacitance of an object placed in proximity to or in contact with the housing. When the capacitance of skin is detected, the circuit is activated, allowing the laser hair removal device to function. The device or the light-generating components therein may be disabled if improper contact is detected in order to avoid misuse. Also, since darker skin tones absorb more light, laser hair removal can potentially be unsafe for different skin tones. For example, certain skin tones will absorb enough light to damage the surface skin layer, while less light will not damage the skin but will also not impact the hair or follicles. Therefore, the skin color detector is positioned in the device, preferably near the output of the device, and is configured to detect the color of the surface in proximity to it. If the skin color or tone is found to be in an unsafe category, the device can be rendered inoperable. Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is perspective view of a handheld hair removal device in accordance with the present invention. 
           [0012]      FIG. 2  is an exploded view of the hair removal device shown in  FIG. 1 . 
           [0013]      FIG. 3  is a perspective view of components of a light homogenizing apparatus in accordance with an embodiment of the present invention. 
           [0014]      FIG. 4  is an exploded view of the homogenizing apparatus shown in  FIG. 3 . 
           [0015]      FIG. 5  is a perspective view of a mounting subassembly which is one of the components of the homogenizing apparatus according to an embodiment of the present invention. 
           [0016]      FIG. 6  is a perspective view of a pair of laser diodes mounted to a contact plate of the mounting subassembly shown in  FIG. 5 . 
           [0017]      FIG. 7  is a perspective view of a light guide of the homogenizing apparatus shown previously in  FIGS. 3 and 4  but now without additional components surrounding it. 
           [0018]      FIG. 8  is a side view ray tracing of light emitted by the laser diodes and propagated through the light guide according to an embodiment of the present invention. 
           [0019]      FIG. 9  is a top view ray tracing of light emitted by the laser diodes and propagated through the light guide according to an embodiment of the present invention. 
           [0020]      FIG. 10  is an expanded view of a side view ray tracing of light exiting the light guide and becoming diffused through a diffuser according to an embodiment of the present invention. 
           [0021]      FIG. 11  is a graph of optical intensity across a range of divergence angles for light exiting the diffuser shown in  FIG. 10 . 
           [0022]      FIG. 12  is a graph of a substantially homogenized output beam in accordance with the present invention. 
           [0023]      FIG. 13  is an exploded view of the front portion of the hair removal device that includes a skin color sensor and a skin contact sensor according to an embodiment of the present invention. 
           [0024]      FIG. 14  is a schematic diagram showing the application of the skin contact sensor works in accordance with the present invention. 
           [0025]      FIG. 15  is an expanded cross-sectional view of the front portion of the hair removal device showing the light path of the skin color sensor in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In General 
       [0026]    Referring now to  FIGS. 1 and 2 , a hair removal device  10  is shown that is sufficiently compact and lightweight so that it may be held in one hand by a user. The device  10  has a housing  12  that includes an arcuate-shaped middle section  14  extending between opposite front and rear ends  16 ,  18 , allowing for a comfortable and ergonomic grip by a user. The user positions the front end  16  of the device  10  towards a location on the body for application of radiative energy towards the epidermis such as for the removal of unwanted hair. Other embodiments of the device  10  may be used for other applications, such as for the removal of skin blemishes. 
         [0027]    The rear end  18  receives electrical energy for powering the device via a cable  20  attached to a suitable external power supply (not shown). The aspect ratio of the housing  12  between the arcuate-shaped middle section  14  and the front and rear ends  14 ,  16  is large, thereby enabling the user of the device  10  to access harder to reach areas on the body. The middle section  14  includes a pair of opposite rubber grip portions  22  that provide a frictional area allowing the thumb and fingers of the user to easily grasp and direct the device  10  towards a target area of application. A button  24  is disposed at a top surface of the housing  12  so that the user may operate the device  10  with a forefinger while the device remains comfortably held. The user may select a power level and be provided with a visual indication thereof by way of an indication strip  26  disposed to emit light out the top surface of the housing  12  between the front end  16  and the button  24 . 
         [0028]    As shown in  FIG. 2 , the device  10  includes various components disposed within the housing  12  that allow for effective operation. Several of the heavier components, including for example a heatsink  28 , are positioned closer to the front end  16 , thereby situating much of the weight of the device  10  in proximity to the grip sides  22  and enhancing the ergonomics of the device. Additionally, a fan  30  that is operable to cool the heatsink  28  is positioned between the grip sides  22  and spins about an axis approximately in line with the longitudinal center of the arcuate middle section  14 . The gyroscopic effect due to the positioning and spin direction of the fan  30  adds stability to the grip of the device  10  thereby also enhancing the effective application of the device. A first and second set of air-flow holes  32 ,  34  penetrating the bottom portion of the housing  12  allow air to flow in and out of the interior of the device  10  so that the fan  30  and heatsink  28  may work in conjunction to cool the device. The holes  32 ,  34  are placed out of the way of the grip by the user to ensure effective heat exchange by the device  10 . 
         [0029]    Light Homogenizing Apparatus 
         [0030]    Referring now to  FIGS. 2-7  a light homogenizing apparatus  40  is shown that is disposed within the housing  12  of the device  10 . The apparatus  40  includes light guide  42  disposed adjacent to and optically coupled with a diode assembly  44 . The diode assembly  44  includes a mounting subassembly  43  formed by a carrier plate  46  and one or more submounts  48  mounted upon the carrier plate  46 . The carrier plate  46  is seated flush to a surface  96  of the heatsink  28 , and a pair of fasteners  50  secures the light guide  42  and carrier plate  46  to the heatsink  28 . The diode assembly  44  also includes one or more single-emitter laser diodes  52  that are mounted adjacent to each other on the one or more submounts  48  and are arranged so that an emitting end  54  of each emits light along a light path directed towards the light guide  42 . The diodes  46  may be attached to or integrated with the carrier plate  46 , however in the exemplary embodiment submounts  48  are used to enhance manufacturability. Beams  58  emitted from each emitting end  54  enter an input end  60  of the light guide  42  and propagate inside towards an output end  62 . An output beam  64  exiting the output end  62  as seen in  FIGS. 8-10  has a homogenized intensity profile  66 , as depicted in  FIGS. 11 and 12 . 
         [0031]    The laser diodes  52  may also be LEDs capable of producing an output beam of similar power, however as shown in  FIGS. 3-6  and  9  each of the diodes  52  are laser diodes. In other hair removal devices, laser diode bars are typically used which tend to require large operating current, such as between 20 and 40 A. Higher operating currents tend to require larger and more expensive current supplies, more batteries, etc. However, by using single-emitter diode lasers  52  it is possible to produce 30 W of power using only 7 A. This enables the selection of a more compact and lower cost power supply to power the diodes  52 . Additionally, the single emitter format combines with specialized optics described herein to allow for a compact and highly ergonomic laser hair removal device. If LEDs are to be used, they would have an alternative configuration within the scope of the present invention, and would include a plurality of LED chips (not shown) capable of producing more than 0.5 W each instead of laser diodes  52 . A high density packaged LED array is capable of applying more than 50 W in a 10 mm by 10 mm area, and is therefore suitable for hair removal. 
         [0032]    The laser diodes  52  may all be selected to emit radiation centered on a particular wavelength, such as 810 nm, or they may selected to emit at different wavelengths. For example, one pair may emit at 810 nm, a second pair at approximately 900 nm, and a third pair at approximately 1000 nm. Different wavelengths may be used for different applications and for different skin colors and may be selectably enabled by the device  10 , such as by way of a skin color sensor assembly (described hereinafter) or a manual user selection. Thus, deeper penetration for darker skin tones can be achieved by using longer wavelengths. The diodes  52  are connected to each other in series with gold wire or other suitable contacting means and driven by approximately 1.85 V each. Thus, as shown the diodes  52  draw approximately 7 A from a 12 V power supply. Other configurations may be used and may be suitable, such as connecting two or more diodes in parallel, depending on the application. 
         [0033]    Referring now to FIGS.  5  and  7 - 9 , each laser diode  52  is capable of emitting a laser beam  58  with a chief ray  68  propagating through a plane  70  that is generally aligned with a length-wise middle cross-section  72  of the light guide  42 . In the exemplary embodiment, the diodes  52  include six diodes  74 A-F grouped in pairs, each diode emitting a respective beam  80 A-F. Each pair has two single-emitter diode lasers  52  each mounted parallel to the other on a submount  78 A-C so that the beams in each pair are emitted in the same direction. For example, diode lasers  74 A,  74 B on submount  78 A emit parallel beams  80 A,  80 B having chief rays  82 A,  82 B at an angle α with respect to a central axis  86  and into plane  70 . Diode lasers  74 E,  74 F are similarly mounted but with an opposite angle β with respect to central axis  86 . Because of opposite angles α, β, the chief ray  82 A of beam  80 A is therefore normally configured to intersect chief ray  82 F of beam  80 F. Likewise, chief ray  82 B of beam  80 B is normally configured to intersect chief ray  82 E of beam  80 E. Diode lasers  74 C,  74 D are mounted so that the chief rays  82 C,  82 D of their respective beams  80 C,  80 D are directed into plane  70  parallel to the central axis  86 . In other embodiments, diodes  52  may have beams directed into planes other than plane  70  and with different angles with respect to each other and with respect to the central axis  86 . 
         [0034]    Referring to  FIGS. 3-9 , the input end  60  of the light guide  42  is disposed adjacent to the submounts  48 , which support the laser diodes  52 , and has a pair of opposite mounting ears  90 ,  92  through which opposite holes are drilled. The mounting ears  90 ,  92  provide a bottom mating surface  94  allowing flush contact with recessed mounting tabs  46 A,  46 B of the carrier plate  46 . The heatsink  28  is disposed below the carrier plate  46  and has a flat surface  96  configured to make flush contact with a bottom surface  98  of the carrier plate  46 . Fasteners  50 , such as hex socket head type fasteners, are first inserted through holes in the mounting ears  90 ,  92  of the light guide  42 , next inserted through holes in the mounting tabs  46 A,  46 B of the carrier plate  46  and then fastened into threaded holes in the heatsink  28  so as to firmly secure the light guide  42  in a given orientation with respect to the carrier plate  46 . In this way, in the exemplary embodiment the middle cross-section  72  of the light guide  42  is generally aligned with plane  70  into which the chief rays  68  of the beams  58  propagate. In other embodiments, different attaching mechanisms may be used to dispose the light guide  42 , carrier plate  46 , and heatsink  28  relative to each other, including but not limited to attaching them to or integrating them into the housing  12 . Additionally, the middle cross-section  72  may be at an angle to plane  70 . 
         [0035]    With respect to the exemplary embodiment, upon exiting the laser diodes  52 , the beams  58  diverge considerably with respect to a first axis  84  that is vertical since the laser diodes  52  are oriented generally parallel with plane  70 . Axis  84  is also referred to as the fast axis since the beam diverges the most across this axis. A corresponding second axis  88 , that is horizontal and slow, i.e., where divergence is minimum, lies generally orthogonal to the fast axis  84  and the direction of the beam. When axes  84 ,  88  are extended in the direction of beam propagation they become planes having characteristic divergences. Also, depending on the geometry and composition of the diode  52  and the positioning of the diode  52  on the submount  48 , a different divergence and relationship between the respective fast and slow axes can result. Separate collimation optics (not shown) may be disposed between the emitting ends  54  of the laser diodes  52  and the input end  60  of the light guide  42 . However, as shown in  FIG. 3 , the light guide  42  is configured to provide the refractive adjustments normally provided by additional optics. As shown in  FIGS. 3 and 7 , the input end  60  has a sharply curved vertical contour and less sharply curved horizontal contour extending in a substantially orthogonal relationship to one another between the mounting ears  90 ,  92 . The curved vertical contour refractively directs the diverging beams  58  to propagate through the interior of the light pipe, as shown in  FIG. 8 . The curved horizontal contour or bulge matches the respective positions of the laser diodes  52  relative to the input end  60  such that the distance between the emitting end  54  and the input end  60  is consistent or close to consistent across diodes. 
         [0036]    As best shown in  FIGS. 3 ,  4  and  7 , the light guide  42  includes a first pair of opposite walls  100  spaced apart from each other and a second pair of opposite walls  102  spaced apart from each other and extending transversely between the first pair of walls  100 . Both pairs of opposite walls  100 ,  102  extend generally between the input and output ends  60 ,  62 . The first pair or relatively vertical walls  100  increase in height linearly as the walls  100  extend from the input end  60  to the output end  62 . Thus, as shown in  FIG. 8 , substantial portions of the beams  80 C,  80 D coupled into the input end  60  become reflected as the beams  58  propagate throughout the light guide  42 . Similarly, other beams  80 A,  80 B and  80 E,  80 F become reflected throughout the interior of the light guide  42 . The refractive index of the material comprising the light guide  42  is sufficiently large compared to media adjoining the second pair or relatively horizontal walls  102  such that total internal reflection is allowed for vertical reflections occurring throughout the interior of the light guide  42 . Total internal reflection may be optimized by also considering the divergence correction achieved by the sharply curved vertical contour of the input end  60  hereinbefore described. The relatively horizontal walls  102  taper in width linearly as the walls  102  extend from the input end  60  to the output  62 . As shown in  FIG. 9 , due to the orientation of the laser diodes  74 A-F and the relatively low divergence across each slow axis thereof, the respective beams  80 A-F do not interact substantially with the vertical walls  100  as they propagate through the interior of the light guide  42 . However, in other embodiments light propagating through the light guide  42  interacts with vertical walls  100  so as to enhance horizontal homogenization of the output beam  64 . 
         [0037]    After expanding the height of the vertical walls  100  and tapering the height of the horizontal walls  102 , the resulting output end  62  has a square to rectangular configuration of approximately 8 mm by 8 mm. As seen in  FIGS. 1 ,  2 ,  9  and  10 , a window  104  made from glass or other suitable material is disposed after the output end  62  and receives the output beam  64  emitting therefrom, and transmits the output beam  64  therethrough so that the output beam  64  may impinge the surface of a target substrate, such as the epidermis of a user. The light guide  42  described herein is highly transmissive, having an efficiency of greater than 90% and emitting light at the output end  62  with exit angles of less than +/−10°. Approximate operating parameters of the exemplary embodiment of the hair removal device  10  include a deposited pulse energy of between 9-20 J/cm 2 , a treatment area of approximately 0.5 cm 2 , a pulse length of between 0.2-0.5 s, a pulse repetition rate of 0.5 Hz, a homogenized intensity profile and exit angle of less than +/−10° produced by the light guide  42 , and in a package having a weight of approximately 0.2 kg. 
         [0038]    In order to make the output beam  64  eye-safe according to ANSI Z136.1 and IEC 60825 using the aforementioned operating parameters, the light of the output beam  64  should be made to diverge by more than one hundred degrees. Adding a typical diffuser to achieve eye-safe divergence, such as an opal or Lambertian type that scatters incoming light in all directions with a cosinusoidal distribution about an axis perpendicular to the scattering surface, would only allow transmission of less than 50% of input light into a usable forward cone. However, a suitable polymer based engineered surface, such as one made by RPC Photonics, can provide the requisite divergence for collimated input beams. Because the light guide  42  provides an output beam  64  that is relatively collimated, such an engineered surface may be included in the homogenizing apparatus  40  in order to achieve the required eye-safe divergence angle. As shown in  FIGS. 9 and 10 , diffusive engineered surface  106  is applied to the input end  108  of the window  104 . The resulting output beam  64  has an eye-safe divergence angle and the transmission efficiency across the diffusing surface  106  is between 80% and 90%. The engineered surface  106  may also be applied elsewhere on the homogenizing apparatus, such as to the input end  60  of the light guide  42 . The intensity profile  66  of the homogenized output beam  64  produced by the homogenizing apparatus  40  with the engineered surface  106  applied to the window  104  is shown in  FIGS. 11 and 12 .  FIG. 11  shows that the intensity profile  66  has losses minimized outside the imposed divergence angle requirement and  FIG. 12  shows the substantial consistency across two dimensions of the intensity profile  66  of the output beam  64  exiting the window  104 . 
         [0039]    Sensor System and Assembly 
         [0040]    Referring to FIGS.  2  and  13 - 15 , the hair removal device  10  is shown to include one or more sensor assemblies disposed near the front end  16 . In order to ensure that the device  10  is contacting the surface of the person&#39;s body, a sensor assembly  110  for detecting touch capacitance is positioned inside the housing  12  and near the output window  104 . As shown in  FIG. 13  in exploded view, the sensor assembly  110  includes a printed circuit board member  112  that provides a base for the sensor assembly  110  and fits into a relief area  114  that surrounds the window  104  on three sides. Two capacitance sensors  116 ,  118  are disposed on the underside of the member  112  and contact the inside surface of the front end  16  of the housing  12 . The sensors  116 ,  118  are wired to a logic circuit attached to the printed circuit board member  112 . As schematically illustrated in  FIG. 14 , the sensors  116 ,  118  detect a change in capacitance through the housing  12  by way of the presence of human touch. The sensor  116  includes a copper piece  120  attached to the pcb member  112  and that is grounded and in series with a microcontroller  113  shown in  FIG. 13 . The housing  12  provides a base capacitance  122  and contact with a person, such as with a finger  124 , provides additional capacitance  126  that is sensed by the microcontroller  113 . Second sensor  118  is positioned on the opposing side of the pcb member  112 . Additional sensors may be included to surround the device, though two sensors are sufficient to ensure sufficient proximity between the housing  12  and the skin surface. Thus, when sufficient proximity is not sensed, the microcontroller  113  can enable the device  10  to become inoperable. 
         [0041]    Referring to  FIGS. 2 ,  13  and  15 , the hair removal device  10  is also shown to include a skin color sensing assembly  128 . The assembly  128  basically includes a printed circuit board member  130 , a holder member  132 , and a light pipe  134 . The light pipe  134  has opposite curved ends  136  with a rectangular profile therebetween, and is shaped so as to fit into a similarly shaped cavity  138  molded into the housing  12 . The light pipe  134  also has a pair of relief notches  140  cut into a top or inner surface thereof. The holder  132  includes a pair of standoff supports  142  interposed between an outer ring halves  144  having similar geometry to the light pipe  134 . The bottom ends of the supports  142  fit into the relief notches  140  of the light pipe  134  and the top ends of the supports  142  fit into holes cut into the pcb member  130 . With compression, adhesive, clasps, or other suitable means, the holder  132  fits between and secures the light pipe  134  and the pcb member  130  of the skin color assembly  128 . The light pipe  134  then fits into the cavity  138  and has bottom surface that becomes exposed to the exterior of the housing  12  through a color sensor aperture  146 . Thus, the skin color sensing assembly  128  becomes disposed in the housing  12  in proximity to the window  104  that transmits the output beam  64  of the device. In other embodiments, the skin color sensing assembly  128 , or skin color sensor aperture  146 , or both, is disposed away from the window  104 . 
         [0042]    The printed circuit board member  130  of the color sensing assembly  128  has a pair of light emitting diodes  148  situated on opposite sides of the standoff supports  142  and directed to emit toward the light pipe  134 . A sensor array  150  is situated on the pcb member  130  interposed between the standoff supports  142 . As shown by the direction arrows in the cross-sectional view of the assembly  128  in  FIG. 15 , light emitted by LEDs  148  propagates through side emission propagation regions of the light pipe  134  and some portion of that light becomes reflected off a surface, such as skin positioned in proximity to the aperture  146 , back through a middle receiving propagation region of the light pipe  134  and is received at the sensor array  150 . The relief notches  140  and respective standoff supports  142  help define these regions by blocking light emitted by the LEDs  148  from propagating directly to the sensor array  150 . A microcontroller  152  shown in  FIG. 13  receives a signal from the sensor array  150  and computes a value that can inform the user of the device  10  of the viability of application to the surface in question. The LEDs  148  can be white LEDs that emit light into a relatively broad spectrum. The sensor array  150  then detects particular wavelengths that have been reflected back and the microcontroller  152  can form a composite value based on the relative quantities of reflected light. For composite values outside of a particular cutoff value the device  10  can be rendered inoperable. The skin color sensing assembly  128  and associated color sensor aperture  146  may be positioned elsewhere on the device  10  as needed. 
         [0043]    The combination of sensor assemblies  110 ,  128  may be applied to other devices as well. For example, a handheld device may include a security feature wherein functionality requires both the detection of skin contact and the detection of a particular skin color or tone. Such a parent device may be one where safety or injury-risk avoidance is a concern, such as a laser hair removal device  10  as described in detail above. Another parent device may be one where security is more of a concern such as an electrical device like a handheld portable communications device. Here the combinations of sensor assemblies  110 ,  128  may serve a lockout function or a personal identity recognition function. Thus, the parent device may only be operated by a user physically operating the device and that matches a particular skin color profile. 
         [0044]    It is thought that the present invention and many of the attendant advantages thereof will be understood from the foregoing description and it will be apparent that various changes may be made in the parts thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely an exemplary embodiment thereof.