Patent Abstract:
Among other things, light that carries information about cooking is directed in a first direction towards a redirection element and, at the redirection element, the light is redirected to be visible to a person cooking.

Full Description:
TECHNICAL FIELD 
     This description relates to displaying cooking-related information. 
     BACKGROUND 
     Electric resistance or induction heating elements used on cooktops do not always provide visual sues to a user about how hot the elements, cookware, or food may be. On some cooktops, status information about cooking is provided implicitly by the controls used to regulate the heating elements or explicitly by displays related to the controls. United States patent application US0024/0238524A1 proposes to warn users when an element is hot using LEDs arranged under the cooktop. 
     SUMMARY 
     In general, in an aspect, light that carried information about cooking is directed in a first direction towards a redirection element, at the redirection element, light is redirected to be visible to a person cooking. 
     Implementations may include one or more of the following features. The information is represented by a color of the light, or by a pattern, an image, a character, or a symbol. The information is modulated by turning the light on and off, light color, and/or light intensity. The light is directed along the first direction through a material which transmits the entire or only a portion of the visible light spectrum. The redirection element comprises a light dispersing element. The light dispersing element comprises laser marked or grit blasted features. The first direction comprises a controlled incoming angle. The information comprises one or more of the following: an on-and-off status, temperature, a temperature distribution, a rate of temperature change, a rate of power change, a desired target temperature, a presence of food, the existence of an usage temperature. The light is delivered from a light emitting diode (LED) and/or a plasma lamp. The light is viewed as emitting from the vicinity of a heating element. The redirection element is in the vicinity of a heating element. The vicinity is directly over the heating element. The light is not located within a cooktop. The light is directed from openings of a light enclosure. The interior of the light enclosure is coated with a Lambertian light reflector. The cooktop surfaces may be coated with a Lambertian light reflector. The cooktop surfaces may be coated with an optically absorptive coating. The redirection element is located within and/or on the surface of a cooktop. The information is displayed by one or more internal redirection elements and/or one or more surface redirection elements. The heating element comprises an induction coil (or any other heating method). 
     In general, in an aspect, a cooktop comprises a material which transmits some portion or the entire visible light spectrum, and a light redirecting element in the material. The light redirecting element receives light from a light source located outside the cooktop. 
     Implementations may include one or more of the following. The light source introduces light into a light enclosure with openings; the light redirecting element receives light escaping from the openings. The interior of the light enclosure is coated with a Lambertian light reflector. The edges of the cooktop are coated with a Lambertian light reflector. The bottom surface of the cooktop is coated with an optically absorptive coating. 
     In general, in an aspect, an apparatus comprises a cooktop and a plasma lamp to provide light visible at an exposed surface to a person cooking. 
     Implementations may include one or more of the following. The apparatus further includes an induction heating element. The plasma lamp is over the induction heating element. The plasma lamp comprises a grounded electrode. The plasma lamp is illuminated depends on an induction heated cookware&#39;s size. The plasma lamp comprises a multiplicity of concentric annuli of light emitting zones. The light is modulated to display the information. The light modulation is a variation in color. The plasma lamp comprises a multiplicity of phosphor layers with different emitted colors. 
     In general, in an aspect, information is determined about a changing state of cooking begin done on a cooking surface, and light that has a characteristic that changes based on the changing state of cooking being done, is made visible to a user in the vicinity of the cooking surface. 
     These and other aspects and features and combinations of them may be expressed as methods, apparatus, systems, program products, in “means for” terminology, and in other ways. 
     Other advantages will be apparent from the description and from the claims. 
    
    
     
       DESCRIPTION 
         FIG. 1  is a top view of a cooktop. 
         FIGS. 2 ,  5 ,  6 , and  8  are schematic side views of cooktops. 
         FIG. 7  is a top view of a plasma display. 
         FIG. 3  is an example of a light enclosure 
         FIG. 4A  is a plan view of cooktop with reflective coated sides 
         FIG. 4B  is a cross section view of cooktop with reflective coated sides 
     
    
    
     Referring to  FIG. 1 , in some examples, visual cues about cooking information related to use of a heating (induction heating, electric heating, or other heating methods) element  10 ,  30  or  40  of a cooktop  12  (or other cooking appliance) can be displayed in a way that enables a user  16  to quickly, accurately, and intuitively understood the state of, for example, the heating element  10 ,  30  or  40 , the cooktop  12 , a cooking utensil, or the food being cooked, and decide how to proceed, for example, by turning on a heating element  10 ,  30  or  40  or keeping clear of a heating element  10 ,  30  or  40  that is hot enough to burn. 
     One portion of the cooktop  12 , a control area  14 , conveys certain kinds of cooking related information to a user  16 . Located in the control area  14 , control knobs  18 , control panel displays  20 , and control buttons  22  display the status of the cooktop  12 . For example, when a heating element  10 ,  30  or  40  of the cooktop  12  has been turned on by turning on a control knob  18 , the position of the control knob  18  indicates something about the cooktop&#39;s status. 
     In the example shown in  FIG. 1 , another portion of the cooktop  12 , a cooktop heating area  24 , also conveys cooking-related information to the user  16 . Lighting elements  26 , which emit or redirect lights, located in the heating area  24  provide information that may be more easily and intuitively seen and understood than information provided in the control area  14 . Light emitted from or redirected by the lighting elements  26  is visible to a user  16  standing near the cooktop  12 . In some examples, the light may also be visible to users  16  standing in other locations farther away from the cooktop  12 . In some examples, the lighting elements  26  are illuminated by a light source indirectly from the side, above, or below the cooktop. In some examples, the lighting elements emit light from a light source such as a plasma lamp. 
     In some examples, multiple lighting elements  26  are arranged at and near each of the heating elements  10 ,  30  or  40  to ensure at least a portion of the lighting elements  26  remain visible to the user  16  when a pot or other cookware (not shown) is placed on the heating element  10 ,  30  or  40 , even though some of the lighting elements  26  may be blocked. 
     In some examples, lighting elements  26  are discrete elements, one or more or a pattern or group of the lighting elements  26  are associated with specific one or more of the heating elements  10 ,  30  or  40  and convey cooking-related information for the associated heating element or elements  10 ,  30  or  40 . Conversely, each of the heating elements  10 ,  30  or  40  can be associated with one or more patterns or groups of the lighting elements  26 . 
     For example, in  FIG. 1 , heating element  30  is associated with a group  32  of lighting elements  26 . Cooking-related information conveyed by the lighting elements of group  32  pertains (at least on some occasions) to heating element  30 . Heating element  40  is associated with a group  42  of lighting elements  26 . Some dual role lighting elements  44  can be associated with both heating element  30  and heating element  40 . For example, when the dual role lighting elements  44  are conveying cooking-related information associated with heating elements  30  by being lit in red to indicate that heating element  30  has been turned on, the lighting elements  44  will also be lit in red. 
     In the examples of  FIG. 1 , the groups  32  of lighting elements  26  are in groups and patterns (in radial lines) around the associated heating element  30 . In some examples, the lighting elements  26  can be arranged in any other kind of pattern or group. The arrangements of the lighting elements  26  in groups and patterns may be designed to serve the purpose of conveying cooking-related information by, for example, placement intended to maximize visibility. 
     The lighting elements  26  can be arranged in a wide variety of shapes and configurations, for example, radially ( 32 ) as shown in  FIG. 1 . The lighting elements  26  can be arranged around the heating element in patterns of varying densities (both densely and sparsely). The lighting elements  26  need not be circular. The lighting elements  26  are not limited to discrete geometrics such as  32  and  42 . The lighting elements  26  can be continuous geometrics. They can be square, triangular, or any standard or nonstandard shape including alphanumeric characters, icons, symbols, words and designs such as  26 - 1  to  26 - 5  in  FIG. 1 . The lighting elements  26  may be arranged in an annular ring (or other shaped) area. 
     Arrangements may be chosen to serve aesthetic purposes. For example, in the patterns of lighting elements  26  in  FIG. 1 , some lighting elements  26  will remain visible to the user  16  even when some of them are obstructed by pots of different diameters. The arrangement also serves an aesthetic purpose because some users  16  find radial arrangements of light attractive. Other patterns (discrete or continuous) that may be useful include arrays, cluster, lines, circles, other geometric groupings, and random groupings. In some arrangements, the lighting elements  26  need not be in the same location as the heating element with which they are associated. 
     A wide variety of properties of the light emitted from or redirected by the lighting elements  26  (in fact, any light property that is perceivable by a user) can be used to encode and convey cooking-related information. The light properties may include individual colors (e.g., wavelengths), sequences of or time changing patterns of colors, ranges or groups of colors, intensities, sequences of intensities, ranges or groups of intensities, and other modulations. The different light properties may be applied to all of the lighting elements of a group or pattern, or only to some of them, or only to one at a time. 
     For example, a bright light or a rapidly flashing light can signify a very hot heating element  10 ,  30  or  40  or pot and a dim light or a non-flashing light can signify a cooler cooktop  12 . A green light can signify that the cooktop is set to a high power-level whereas a blue appearing light can signify low power level. 
     A wide variety of cooking-related information can be conveyed using the lighting elements  26  and groups and patterns of them. The cooking related information could include status information about elements of the cooktop  12 , including about the cooktop  12  as a whole, one or more of the heating elements, one or more pots or other items of cookware that are on one or more of the heating elements, the food that is being prepared in one or more of the items of cookware, and other information. Status information may include a power level of a heating element  10 ,  30  or  40 , a temperature of a heating element  10 ,  30  or  40  when the heating element gets hot, a desired or intended temperature of a heating element  10 ,  30  or  40 , a temperature distribution of the heating element  10 ,  30  or  40 , a rate of change of temperature of a heating element, a temperature of a pot or other cookware, a desired or intended temperature of a pot or other cookware, a rat of change of temperature of a pot or other cookware, an elapsed time (count-up timer), a remaining time (count-down timer), a presence of food in one or more pots or other cookware, and a current measurement of mass of food in one or more of the pots or other cookware. This cooking-related information can enhance the user&#39;s cooking experience and safety. For example, knowing the heating rat of the cookware can help a chef produce more appetizing food. Knowing the time elapsed (or time remaining) since the heating element  10 ,  30  or  40  has been turned on or has reached a desired temperature can assist a busy cook by tracking the time remaining for a dish. Knowing the temperature of the pot can reduce the chance of the user  16  (or the food) being burned. When more than one item of food is being cooked on more than one heating element, the lighting elements  26  can be used to guide the user  16  with respect to the order in which different pots or cookware need attention. The cooking-related information could indicate the stage of cooking with respect to the steps of a recipe. 
     A wide variety of techniques and device can be used to provide the lighting elements  26 . In some examples, the lighting elements  26  are illuminated by a light source indirectly from the side, above, or below the cooktop. In some examples, the lighting elements  26  are one or more plasma lamps. 
     In some examples, as shown in  FIG. 2 , the lighting elements  26  are light redirecting elements, which may be discrete or continuous, arranged to show certain features or patterns  50  within or on a surface (either the top  52  or bottom  53  surfaces) of a glass layer  54  that forms part of the cooktop. When the features  50  are within the glass  54 , they may be located at any distance from the top or bottom planes  56 ,  58  of the glass layer, for example at approximately the midplane of the glass thickness. In the example of  FIG. 2 , the light is delivered to the features  50  from a side  64  of the cooktop. 
     As mentioned earlier, the features  50  can be discrete or continuous and can take on any of a wide variety of forms and shapes, including spheres, teardrops, cubes or concentric rings, squares, radially configured circles or rectangles, or lines. The features  50  can be either directly under (for internal features), or on (for surface features) the surface of the cooktop, and be placed in close proximity to a heating element  10 ,  30  or  40  so that the cooking-related information for the heating element  10 ,  30  or  40  can be displayed. 
     The glass layer  54  can be made of glass ceramic material similar to that often used in cooktop  12  which has good resistance to high temperatures, thermal cycling and high fracture resistance. In general, as a glass, glass ceramics have composition Li 2 O—Al 2 O 3 —SiO 2  an other phases in very small percentage additions which are used as nucleating agents. Some examples of nucleating agents are TiO 2 , ZrO 2  and P 2 O 5  Nucleating agents enable the desirable properties of the glass ceramic to be achieved. Some trade names for glass ceramics which may be used for cooktop applications are EuroKera, Neoceram, Robax and Ceran. 
     The cooktop features can be achieved by laser marking, chemical etching, plasma etching, grit blasting, or in other ways. In addition, the glass  54  can be formed originally to have light dispersing features on its surfaces or internally. 
     When light from a light source  66  (for example, LEDs or conventional lamps) shines onto the internal or external features or other redirecting lighting elements, the redirecting lighting elements such as the internal features  50  or surfaces features  52  or  53 , redirect the light to give the appearance that the lighting elements  26  themselves are emitting light  63 . Visually attractive displays may be achieved by the arrangement of the redirecting lighting elements  26 . The redirecting lighting element  26  (the internal or surface features) can then be used to emit a light signal for conveying information about cooking. For example, referring again to  FIG. 1 , when light is redirected by internal or surface features  26 - 5  to display the characters “ON”, the user  16  will read the work “ON” as it is being projected from the internal or surface features. 
     Referring again to  FIG. 1 , in the case of induction heating element, for example,  30 , the lighting elements  26  can be arranged directly above an induction coil (heating element  30 ) between the induction coil  58  and the portion of the cooktop which bears the pot or cookware. An induction coil  68  uses induction heating to heat food. Typically, a ferromagnetic (or ferromagnetic-coated) pot is placed above the induction coil  68 . An induction current in the induction coil produces a rapidly oscillating magnetic field near the surface of the cooktop  12 . The oscillating magnetic field is converted into heat in the ferromagnetic pot. Magnetic hysteresis enhances the heating effect for ferromagnetic materials. The magnetic field also produced electrical eddy currents in the metal base of the pot to produce resistive heating. 
     In some examples, the LEDs as light source are placed to the side  64  away from the induction heating element  30 . This arrangement avoids potential damages from heat and the oscillating magnetic field which may affect the LED circuitry and causes LEDs to flicker. Furthermore, LEDs can be maintained and replaced more easily. 
     As shown in  FIG. 2 , a control system for controlling the light  63  that is redirected by the lighting elements  26  accepts information regarding the user&#39;s actions from the user power controls  60 . Based on this and possibly other information (for example information about induction coil power, cooktop/pan/food temperature, intended recipes, maximum permissible cooking times, other foods being cooked on other elements), the control system coordinates the illumination of the lighting elements  26  (features  50 ) over time. Through the controlled illumination, information about cooking is conveyed to the user. 
     For example, to boil a pot of water on induction heating element  30 , the user turns on the heating element  30  using the user power controls  60 . The user&#39;s action is sent to an LED controller  76  and to an induction power supply  77 . The induction power supply  77  delivers a corresponding amount of power to the induction heating element  30  to heat the water in the cookware. 
     The induction power supply  77  also sends a signal to the LED controller  76  which incorporates this information in its control of the light source  66 . As the cookware is heated, the temperature of the cooktop is detected by one or more nearby temperature sensor  79  and the temperature of the pot is inferred from the temperature of the cooktop. The temperature may also be directly sensed within the cookware, or derived from the applied system load or other characteristic properties of the coil/target system. It should be noted that other sensors for providing other cooking information such as presence of food can also be used. The temperature sensor  79  sends a temperature signal to the LED controller  76 . The LED controller  76 , based on cooking information signals from the user power controls  60 , power supply information from the induction power supply  77 , and temperature information from the temperature sensor  79 , generates and sends LED control signals to the lighting source  66 . Light  62  from the light source  66  illuminates one or more lighting elements  26  based on the LED control signal. The lighting elements  26  redirect light  63  (such as through scattering) from the light source  66  and convey information to the user  16 . The light source  66  may be standalone LEDs or LED arrays  80 . 
     Although  FIG. 2  shows the light  62  from the LEDs  80  projected from the side  64  of the cooktop, the light can also be projected from below or above the cooktop. 
     In some embodiments, the light  62  can be delivered to the cooktop through light pipes, fiber optic cables, mirrors, and other optical elements. 
     Light  62  from the light source  66  travels through the cooktop glass  54  to the lighting elements  26  by internal reflection  82 . To achieve this, the angle  83  of the light from the light source  66  entering the glass cooktop  54  from the side  64  is controlled. For internal features  50 , the incoming angle  83  of the light leads to total internal reflection (TIR) of the LED light  62 . For surface features  52  the incoming angle  83  of the light can be set to the critical angle relative to the top surface  56  of the glass cooktop  54  to lead to development of a cooktop surface light ray traveling on the top surface  56  of the cooktop. For surface features  53  the incoming angle  83  of the light can be set to the critical angle relative to the bottom surface  58  of the glass cooktop  54  to lead to development of a cooktop surface light ray traveling on the bottom surface  58  of the cooktop. Surface features  52 ,  53  could also be illuminated from an indirect source located below the cooktop (see below for more details). In some examples, both internal features and surface features are employed for conveying cooking information. For example, internal features  50  can be used to indicate power on and variant power (by variable intensity), and surface features  52  and/or  53  can be used to indicate temperature variation. Internal features  50  and surface features  52  or  53  can be in different colors and/or patterns. 
     As in an optical fiber, a portion of the light  62  from the light source stays within the transmission medium (the cooktop glass  54 ). As measured between the light ray  62  and the perpendicular vector to the cooktop glass surface, if the angle of incidence  83  from the light source  66  is larger than the critical angle, the light  62  is internally reflected within the cooktop glass  65 . Achieving an incident angle greater than the critical angle insures that the maximum amount of light is imparted to the glass, thus allowing the maximum amount of light to be available for redirection by the lighting elements. Light  62  traveling within the glass  54 , is largely inconspicuous to the user until it encounters the lighting elements  26 , which redirect the light  62 . In this case, the features  50  effectively scatter the light in a conspicuous manner. Because light traveling within the glass is only evident at the features  50 , the light  63  appears to the user  16  to origins from these features  50 . 
     The critical angle is based on the index of refraction of the glass and of the air using Snell&#39;s Law. Any material that is optically transmissive and can withstand the cooking environment is a suitable candidate as a cooktop substrate. When the light travels in a glass ceramic cooktop  54 , as the glass ceramic material has a general transmission of 90% in the visible spectrum, the light travels mostly unimpaired through the cooktop  54  until it hits the features  50 . 
     A wide variety of light characteristics can be varied to convey a variety of information can be conveyed to the user. In some examples, the light source  66  can emit light  62  in selected wavelengths and polarities. The light source  66  may be different colored LEDs angled at different directions. The features  50  may be designed to act differently with respect to different polarization states of light, and thus light elements of different polarization states can occupy the same position on the cooktop surface. 
     The features  50  can be designed to redirect the light  62  from the light source  66  in a variety of different ways. For example, the light  62  can be redirected in a specific number of specific directions or it can be scattered and diffused indiscriminately. The light  62  can be redirected by features within the glass  54  (Or on the glass) that are arranged in places  65   a ,  65   b  as the light reflects from the different planes  65   a , and  65   b . These planes can be arranged to impart aesthetic or informational features to the redirected light. In the case in which the light  62  is redirected by indiscriminating scattering, the features are not arranged in any specific plane  65   a  or  65   b . Rather, the features scatter light to create a fuzzy-looking glow. 
     An advantage of using features  50  within or on the glass is that the features  50  can be placed near areas of intense heat without fear of damage as they are an integral constituent of the glass itself. This permits placement of the lighting elements in places that would not be suitable for light sources  66 . For example, LEDs do not have the thermal stability to be placed near open gas flames or electric heating coils 
     The redirecting light elements  26  also permit easy replacing or switching of the light sources  66  that serve them. Among other things, the light sources  65  can be placed in an easily accessible area to enable the user  16  to change the light sources  66  (e.g., to replace a burnt-out light source, change the color, or upgrade to a more energy efficient source). In addition, if the supporting cooktop  54  is damaged, the supporting cooktop  54  can be replaced independently of the light source  66 . The user may change the supporting cooktop  54  for other reasons, for example, to change the features  50  for aesthetic purposes. Because the lighting elements  26  are separate from the light sources  66 , manufacturers can produce different models of cooktops that use a common set of lighting sources while changing the features from model to model to serve a variety of different purposes. 
     In some examples as shown in  FIG. 3 , light is captured within a geometric form light enclosure  46  which is designed for having total internally reflected light. The light will be let out only at openings  48  which have been designed to achieve maximum lighting elements (e.g., features  50 ,  52  or  53  of  FIG. 2 ) illumination. In some examples, the light enclosure  46  can be placed between a heating element, such as an induction heating element  30 , and cooktop glass. The interior surfaces of the light enclosure  46  can be coated with a material to produce a Lambertian light reflection to ensure that light only escapes at the desired location and with maximum intensity. The openings may be in the form of slits, slots, circles, triangle, wedges, squares, or any other geometry. Light from light source such as LEDs, fiber optic bundles, or conventional light sources can be introduced into the geometric form light enclosure  46  along its outer circumferential wall through openings  47 . These light sources can be arranged at an angle to achieve maximum light intensity at the exit ports. Further, multiple light colors can be contained and redirected toward features ( 50 ,  52  or  53  of  FIG. 2 ) by using internal dividers  49  within the closed light enclosure  46 . This allows a distinct colors to be independently displayed on the cooktop surface simultaneously. 
     In some examples as shown in  FIGS. 4A and 4B , the top view and cross section view of the sides of the cooktop glass  54  which is coated with a Lambertian light reflector  59  to prevent light from escaping at the edges, and to provide a more uniform and more intense illumination of the features  50 . The edge where the light is initially imparted to the cooktop glass can also be coated with the reflective coating to leave only the areas where light enters the glass uncoated. This will assure that the great majority of the light is trapped within the cooktop glass and is available for features  50  maximum illumination. 
     In some examples, as shown in  FIGS. 4A and 4B , the bottom surface  58  of the cooktop glass  54  is coated with an optically absorptive coating  61  such as a black paint. This assures that any light which is refracted out of the glass ceramic at its bottom surface will be absorbed and thus not produce a diffuse reflection. As needed, areas of the bottom of the glass ceramic cooktop can be masked so as to allow light to escape from the light volume. 
     In some implementations, the light source  66  may be one or more plasma lamps  90   a ,  90   b  (collectively  90 ). Referring to  FIG. 5 , a plasma lamp (PL) controller  92  accepts information from the user power control  60 , the induction power supply  77 , and temperature sensor  79 . Based on this and possibly other information, the controller  92  coordinates how and when a plasma lamp  90  is illuminated. The controlled illumination conveys information about cooking to the user  16 . 
     The plasma lamp  90  can be built into a cooktop  54 , (e.g., an induction cooktop) so that a flickering or moving glow appears under or in the vicinity of the pot or other cookware being heated. Although induction heating is invisible the plasma glow from the lamp  90  located under the pot can be used to simulate heating by another type of heat, for example, a gas flame. One type of plasma lamp that can be used is described in U.S. Pat. No. 5,383,295. 
     The cooing-related information provided to a user  16  of the cooktop using the plasma light  90  could include the amount of heating power applied by the induction power supply based on a color and/or intensity of the plasma light  90 . A change in the amount of power being supplied could be indicated by a change in the color or intensity of the plasma light  90 . In some embodiments, the relationship between the colors and power levels can follow a blackbody curve (red=low, yellow=medium, white=medium high, and blue=high). Other color-to-power level relationships may be selected based on psychological associations of various colors with information, for example blue=low and orange or red=high. 
     By adjusting the parameters of the plasma discharge or using diffusers, the plasma can appear warm and fuzzy rather than as a dangerous-looking lightning or sparing effect. The plasma lamp  90  contains gases and phosphors in the plasma discharge region. The colors can be produced by changing these gases and/or phosphors. The position of the plasma generation can also be controlled through modifying electrode geometrics. 
     Power for the plasma stimulation can be from a separate power supply or from an existing power supply. If a separate power supply is used, a conventional high-voltage, high frequency power supply may power the plasma lamp. If an existing power supply used, the existing induction power supply  77  can be modified to produce high frequency components so that an additional power supply is not necessary. 
     Referring to  FIG. 6 , in some embodiments, a plasma lighting system  100  can be designed to use two phosphors by applying each phosphor to opposite sides  102   b ,  104   a  of a glass plate  103 . Plasma lamp is a sandwiching of five glasses: a top glass  101 , a top spacer glass  102 , a middle glass  103 , a bottom space glass  104 , and a bottom glass  105 . A cavity  106  is formed by the middle glass  103 , a spacer glass  102 ,  104 , and either the top  101  or bottom  105  glasses. Xenon gas fills the cavity  106  and various combinations of phosphor line a portion of the cavity&#39;s walls. 
     In some examples, orange phosphor lines a portion  108  of the cavity  106  formed by the top side of the middle glass  102   b  and blue phosphor lines a portion  110  of the cavity  106  formed by the bottom side of the middle glass  104   a . Each side is energized separately by a low frequency power supply (typically 60 Hz)  112 ,  114 . The low frequency prevents the electricity from energizing the opposite side. By continuously varying the electrical stimulation of each side, a full range of colors is produced that varies from blue to orange. The intermediate colors include shade of magenta. The intensity of the light (brightness) can also vary at the same time the color goes from blue to orange. For example, the intensity may gradually increase during the blue to orange transition. In come embodiments, the blue phosphor is placed on the side opposite the view, the bottom side of the middle glass  104   a , because the blue is brighter than the orange. 
     To avoid electrically charging the cookware and giving the user a shock or tingling sensation when the user that touches the pot, the plasma could be adequately grounded to remove the electrical charge. Referring to  FIG. 6 , in some embodiments, electrodes  116 ,  118 ,  120 ,  122  are included in plasma light were electrodes  118 ,  122  are grounded. This effectively prevents electrical charges from being induced in the pot. 
     Referring to  FIG. 7 , various plasma geometries can be used. One example uses concentric circles  124 . The plasma is trapped within a circular annulus that is approximately ¼ side. This arrangement makes the flickering plasma light appear alive. The width of the circular annulus may be sized to the user&#39;s desires. The circular annulus does not extend completely around the circle. This forces the low frequency current to travel uniformly from one electrode to the other. 
     Referring to  FIG. 8 , the plasma lighting  90   a ,  90   b  an be combined with LEDs  80  to produce a variety of effects such as the ability to independently signal when the cooktop  54  is hot (temperature) and when the induction coil  68  is energized (power). For example, red LED&#39;s can signal hot cooktop  54  and blue plasma can signal energized induction coil  68 . Electrodes or coil pickups can be used to couple the LED with the plasma. 
     Other embodiments are within the scope of the following claims.

Technology Classification (CPC): 5