Abstract:
An underwater lighting fixture adapted for installation in a lamp receiving recess in the wall of a swimming pool. The fixture includes a lamp housing having a pair of reflector-mounted incandescent lamps mounted therein. A plate having a pair of a apertures is mounted in the housing with the apertures mounted in alignment with the lamps. A pair of secondary reflectors are mounted to face the plate apertures and are provided with light-transmitting portals. A color wheel having dichroic filter segments is mounted so that identically colored pairs of segments pass the portals when the color wheel is driven by a motor. The motor is controlled by a circuit by disconnecting power to an input of the circuit, reconnecting power to the input to control the motor to move at a first speed. The control circuit stops the motor when the driven element reaches an index position. After the step of reconnecting power and after a predetermined period of time, the control circuit controls the motor to move the driven element at a second speed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of illumination, and, more particularly, to a submersible color light. Although the present invention is subject to a wide range of applications, it is especially suited for use in a pool lighting system, and will be particularly described in that context. 
     BACKGROUND OF THE INVENTION 
     Pool lights illuminate the water at night for the safety of swimmers and for aesthetic purposes. The illumination emanates from underwater lights affixed to the wall of the pool. As used herein, a pool is used generically to refer to a container for holding water or other liquids. Examples of such containers are recreational swimming pools, spas, and aquariums. 
     To enhance the aesthetics, some current underwater pool lights use a transparent color filter or shade affixed to the front of the lens of the pool light to filter the light emanating from the lens of the pool light and thus add color to the pool. The color filters come in a variety of colors but only one of these color filters can be affixed to the pool light at a given time. Thus, the color of the pool stays at that particular color that the color filter passes. In order to change the color of the pool, the color filter must be removed from the pool light and a different color filter installed across the lens of the pool light. 
     As a alternative to these fixed colored filters, a system has been devised whereby a rotating wheel having filters of several colors is provided, such as the system disclosed in U.S. Pat. No. 6,002,216 and incorporated herein by reference. In this arrangement, white light is provided from a single source to at least one fiber optic lens through an optical fiber. Colored light is emitted from each fiber optic lens by passing white light through the color filter wheel which is selectively rotated by a motor in the illuminator. The color of light emitted by multiple illuminators is synchronized by independent circuitry within each illuminator that responds to digital signals in the form of manually interrupted supply current. 
     However, fiber optic underwater illumination systems have several limitations that lead to the need for the present invention. The first is that their performance is relative to the skill of the installer. Only a well-trained technician is capable of installing a fiber optic system that can adequately illuminate a swimming pool. The availability of qualified training is limited thus the availability of trained installers is limited. Rushed fiber termination or fiber termination performed by an untrained installer can result in more than a 30% decrease in fiber optic system performance and can ultimately result in a costly failure of the total fiber optic system. 
     The second disadvantage of underwater fiber optic illumination is the limited amount of light delivered to the pool. This results from the light attenuation over distance that is inherent in the fibers&#39; composition and the inefficiencies of focusing available light into the optical fiber at the light source. 
     A further drawback of fiber optic underwater illumination is in the possibility of retrofitting the millions of existing pools having traditional submersible incandescent lighting fixtures. The feasibility of installing adequately sized fiber optic cable in the existing conduits is limited. These conduits are commonly ½ inch in diameter and are rarely over one inch in diameter. The minimum conduit diameter to carry a single fiber optic cable capable of delivering minimally acceptable light to a pool is one inch and the recommended size is 1½ inches. 
     An additional limitation of fiber optic systems is the additional cost of the materials and professional installation. 
     The alternative to colored fiber optic systems, providing colored lenses to submersible incandescent lighting fixtures, can be troublesome as well. These fixtures can be supplied with a colored glass lens to deliver that specific color to the pool. These colored glass lenses are typically limited to how richly they can color the light because the darker (or richer) the lens color, the more light in the form of heat that is trapped in the lens and the fixture. As the lens becomes too hot by absorbing too much light it can break due to thermal expansion or due to the differences in thermal expansion on the hot interior surface of the glass and the cool exterior surface that is in contact with the water. Further, as a result less light is emitted and it may be insufficient to illuminate the pool. 
     As an alternative to glass lenses, snap on or twist lock plastic colored lenses can be installed over an existing clear glass lens for a considerably simpler method to changing the color of the pool lighting. This method still requires physically lying or kneeling on the edge of the pool an reaching below the water to remove the existing plastic lens and then reaching again into the water to install the next colored plastic lens. Economical transparent colored plastics are also inefficient light transmitters reducing the amount of colored light reaching the pool. 
     A need therefore exists for pool lights that can easily replace existing self-contained, incandescent lighting fixtures, but having synchronized color wheels without the additional cost of installing fiber optic cables and other drawbacks associated with fiber optic underwater illumination systems. Further, a need exists for colored lenses to be used with incandescent fixtures that do not trap excessive amounts of light and heat. 
     SUMMARY OF THE INVENTION 
     The present invention, which tends to address these needs, resides in a pool lighting system. The pool lighting system described herein provides advantages over known pool lighting systems in that it is less difficult and less costly to install than existing pool lighting systems that can provide a variety of synchronized colors to the pool water and can be easily retrofitted to existing incandescent lighting systems. 
     According to the present invention, each lighting fixture of the pool lighting system comprises a color wheel and an incandescent lamp, wherein the lighting fixture places the color wheel at a predetermined position after a predetermined time subsequent to an alternating-current (AC) source of power being applied to the lighting fixture. 
     Further, according to the present invention, an underwater lighting fixture includes a lamp housing which is adapted to be installed in a lamp receiving recess in the wall of a swimming pool. The housing has an interior cavity, an open mouth defined by a rim, and a rear opening. A plate is mounted within the housing and is transverse to a longitudinal axis of the housing. The plate has a pair of diametrically opposed openings. A pair of incandescent lamps are positioned at each of the plate openings on one side of the plate and each lamp is provided with a reflector directed toward its plate opening. Secondary reflectors are positioned on the other side of the plate so that the reflectors have mouths at one end which are directed toward the plate openings. Each secondary reflector has a portal at its other end which is directed toward the mouth of the housing. A color wheel which is mounted for rotation in the housing about the longitudinal axis of the housing. The color wheel has a plurality of radial dichroic filter segments which are arranged so that identically colored segments are diametrically opposed on the wheel. The wheel is driven by a motor to sequentially position successive filter segments over each reflector portal. A transparent cover is sealed to the open mouth of the housing and an electrical supply conduit extends through a fluid seal in the rear housing opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a submersible lighting fixture mounted in a pool wall; 
     FIG. 2 is a cross-sectional view, the plane of the section being indicated by the line  2 — 2  in FIG. 1; 
     FIG. 2 a  is a cross-sectional view, the plane of the section being indicated by the line  2   a — 2   a  in FIG. 2; 
     FIG. 3 is a perspective view of a submersible lighting fixture shown with its transparent cover removed; 
     FIG. 4 is a fragmentary perspective view of the submersible lighting fixture shown with its transparent cover and color wheel removed; 
     FIG. 5 is a back plan view of the color wheel of the submersible lighting fixture; 
     FIG. 6 is a detail of the submersible lighting fixture illustrating the alignment of a sensor and a magnet disposed therein; 
     FIG. 6 a  is a detail of the engagement between a worm gear and a ring gear in the present lighting fixture; 
     FIG. 6 b  is a detail of the engagement between a conventional worm gear and a ring gear; and 
     FIG. 7 is an electrical schematic of a synchronizer circuit of the lighting fixture. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in the drawings, and with particular reference to FIGS. 1 and 2, the present invention is embodied in a submersible incandescent lighting fixture  10  comprising a housing  12  having an open mouth  15  and defining a cavity  15   a  with a rear opening  15   b.  A component tray  14  is mounted on the housing  12 . The lighting fixture  10  is adapted to be mounted in a recess  11  in a wall  13  of a pool. A power cord  16  extends from the housing  12  through the opening  15   b  and is sealed by a grommet  15   c  to provide power to the lighting fixture  10 . 
     Referring to FIG. 2, to provide light to a pool, the lighting fixture  10  further comprises two lamps  18  with integral dichroic-coated glass reflectors  19  having axial grooves  19   a  therein and two secondary reflectors  20  mounted to a copper plate  22 , the plate  22  being mounted to the housing  12  and having a pair of diametrically opposed openings  22   a  and  22   b.  The secondary reflectors  20  extend through two circular passages  24  provided in the tray  14 . The secondary reflectors  20  are provided with circular portals  23  to allow the passage of light emanating from the lamps  18 . The portals  23  are relatively small in area compared to the openings  22   a  and  22   b  and bottom openings  20   a  and  20   b  in the secondary reflectors  20  are relatively large in area compared to the openings  22   a  and  22   b.    
     The contact areas between the lamps  18 , a copper plate retainer  25 , the copper plate  22 , and the metal housing  12  allow heat generated by the lamps  18  to be efficiently transferred to the housing  12  and dissipated into the pool water. Thus, the lighting fixture operates at a cooler temperature and the life of its components, including the lamps  18 , is increased. 
     Referring to FIG. 4, the tray  14  is further provided with a center post  26  and a sensor guide  28 . Affixed to the tray  14  is a printed circuit board  30 , a driver mechanism  32 , and a sensor  34  extending from the circuit board  30  and disposed within the sensor guide  28 . 
     Referring now to FIGS. 3-6, a color wheel  36  is mounted on center post  26 . The color wheel  36  comprises a ring gear  38 , a magnet  40 , and three pairs of dichroic glass filters  42 ,  44  and  46 , as best shown in FIG.  5 . The color wheel  36  is disposed in front of the lamps  18  so that light emitted by the lamps  18  when energized, passes through the color wheel  36 . Dichroic filters are used, as opposed to colored glass or other types of filters, because they allow the greatest amount of light to pass through, reducing the amount of light absorbed as heat and providing more intense colors. Except for the magnet  40  and filters  42 ,  44  and  46 , all of the components of the color wheel  36  are made from a transparent, colorless material so as not to interfere with the emission of light from the lighting fixture  10 . 
     The driver mechanism  32  is comprised of a stepper motor  48  and a worm gear  50  that rotate the color wheel  36  through a connection to the ring gear  38 , a best shown by FIG.  3  and FIG.  5 . Such a connection eliminates the need for a shaft connecting the color wheel  36  to the stepper motor  48 , as in U.S. Pat. No. 6,002,216. Such a shaft would require tedious realignment each time a burned-out lamp needed to be replaced. The use of the worm gear  50  and ring gear  38  allow the entire color wheel drive train to be contained in front of the lamps 
     Referring now to FIGS. 6 a  and  6   b,  a conventional worm gear  50 ′ and ring gear  38 ′ engagement is shown in FIG. 6 b.  In this arrangement, it is necessary for the worm gear  50 ′ to be precisely aligned to a line  50   a ′ being parallel to a line  38   a ′ being tangent to the ring gear  38 ′ at the point of engagement. In this conventional design, if the worm  50 ′ is angularly misaligned, a tooth  50   b ′ of the worm gear  50 ′ may be unable to freely move within the space between teeth  38   b ′ of the ring gear  38 ′. The present invention, in order to solve this problem of gear binding, provides the worm gear  50  with a slightly undercut tooth  50   b,  as shown in FIG. 6 a.  As will be appreciated by one of skill in the art, this undercut tooth  50   b  allows for a certain amount of angular misalignment, φ, between the longitudinal center-line  50   a  of the worm gear  50  and a line  38   a  being tangent to the ring gear  38  at the point of engagement, without any binding occurring. 
     Referring again to FIGS. 3-6, as the color wheel  36  is rotated, the pairs of filters  42 ,  44  and  46  pass sequentially in front of the lamps  18 , filtering the light emanating from the lamps  18 . The filtered light is transmitted to the pool through a lens or transparent cover  60  mounted to the front of the housing. 
     The pairs of filters  42 ,  44  and  46  allow the passage of a specific wavelength of light: green, blue and red/magenta, respectively. A pair of openings  51  are also provided on the color wheel  36  to allow for the passage of white light. When a combination of two adjacent filters of different colors, or a filter and an opening  51 , are simultaneously positioned over a single lamp  18 , the light emitted from the lighting fixture  10  has the appearance of being a mixture between the two colors being passed through, the particular hue being determined by the relative proportions of light passing through each filter or opening  51 . For example, the blue filter  44  and red/magenta filter  46  could be combined to produce light at nearly any hue of purple. The filters  42 ,  44  and  46  are sequentially arranged in spectral order, with green  42  isolated from red/magenta  46 . Thus, rotation of the color wheel  36  gives the appearance of a subtle, nearly indistinguishable transition from one hue to the next. 
     It should be noted that the portals  23  provided between the lamps  18  and the color wheel  36  serve a variety of purposes. The portals  23  limit the light that is emitted to the area with the greatest flux density (the primary focus spot), minimizing the size of the dichroic filters  42 ,  44  and  46  and the color wheel  36  and thus reducing the cost and overall size of the lighting fixture  10 . Additionally, it is necessary to mask the light emitted so that it does not pass through unintended adjacent filters. As will be appreciated by one of ordinary skill in the art, dichroic filters require light to strike them in a generally perpendicular fashion in order to produce predictable results. The farther in either direction from perpendicular that light strikes a dichroic filter, the greater the variance from the desired hue will the light be that passes through. Thus, the small size of the portals  23  is necessary to prevent scattered light from striking the dichroic filters at shallow angles and tainting the desired hue. 
     In the present embodiment the lamps  18  utilized are 75-watt, 12-volt lamps having integral reflectors. The lamps  18  are selected to have optimal characteristics, such that a sufficient amount of light can be generated but the lamps still have an acceptable life and efficiency. The filters  42 ,  44  and  46  and the openings  51  are arranged with bilateral symmetry on the wheel  36 , such that the same filter/opening combination and proportion appears in front of each lamp  18  at any given moment. 
     To further enhance the efficiency of the lighting fixture  10 , the use of secondary reflectors  20  allows much of the light that does not directly pass from one of the lamps  18  through the corresponding portal  23  to be reflected back into the primary reflector  19  and finally out through the portal  23 . Thus, the secondary reflectors  20  take otherwise wasted light that is outside the primary focus spot and reflect it back to the primary reflectors  19  where it is then reflected forward to the useable primary focus spot. 
     Referring now to FIG. 6, the color wheel  36  is shown rotated such that the magnet  40  is aligned with the sensor  34 . This alignment provides a magnetic indexing point, such that the sensor  34  is responsive to the position of the color wheel  36  and provides a reference position pulse indicating the color wheel is at a predetermined position when the magnet  40  passes over the sensor  34 . The sensor  34  is a readily available magnetic field detector that generates a reference position pulse when in close proximity to the magnetic field generated by magnet  40 . 
     Referring again to FIG. 2, the lighting fixture  10  is provided with an integral transformer  52  that converts alternating current line voltage into power suitable for the circuit board  30  and the stepper motor  48 . The integral transformer  52  allows the lighting fixture  10  to easily replace existing 120 volt light fixtures with little effort and it avoids many of the problems associated with connecting a plurality of low voltage lighting devices to a single transformer, including the risk of overloading the transformer. Additionally, the integral transformer  52  allows the use of 12-volt lamps, since present technology limits viable, bright, compact, long-life lamps with integral reflectors to low voltage. A thermally conductive resin  54  secures the transformer  52  to the housing  12  and transfers thermal energy therebetween which is eventually dissipated by the housing  12  into the pool water. 
     The interior of the cavity  15   a  is sealed from fluid by the lens or transparent cover  60  and a sealing grommet  62 . The grommet  62  is seated in a peripheral lip  64  of the housing  12  and is covered by a trim seal ring  66 . The seal ring  66  has a plurality of depending hooks  68  which are pivotally connected to the ring  66  and which receive an annular tensioning wire  70 . The wire is tensioned by a tensioning bolt (not shown) which, upon tightening, draws the hooks into contact with the lip  64  to compress the grommet  62 . The sealed housing  12  is retained in the recess  11  by a screw  72  located at the top of the housing  12 , as mounted in the recess  11 , and by a tab  74  located at the bottom of the housing  12 . The interior of the recess is flooded with water for cooling purposes by providing a plurality of openings  76  in the seal ring  66 . The colored or white light admitted through the color wheel is further dispersed by a lens texture  60   a  molded into the cover  60 . 
     A synchronization circuit is-provided on the circuit board  30 . The circuit operates in a way that allows multiple light fixtures  10  to be synchronized without the need for additional wiring between units. 
     In the present invention, the synchronization circuit uses the 60 Hz alternating current supply voltage to generate a master pulse. Thus, the same master pulse is generated by every lighting fixture that is connected to the same power source. Accordingly, there are no slave units and no need for wiring from a master unit to slave unit in order to transmit the master reference signal to each slave unit. 
     The synchronization circuits are controlled by timed interruptions in the alternating current supply voltage. Each power interruption is used as a reference point by the synchronization circuits allowing all of the color wheels to be synchronized and the same accent color from each of the light fixtures to be provided to the pool water. 
     The synchronization circuit of each light fixture synchronizes the color wheel by controlling the driver mechanism to place the color wheel at a predetermined position subsequent to the alternating-current source of power being interrupted in a predetermined sequence. This assures that the color wheels are synchronized. 
     After a predetermined time, the synchronization circuits begin stepping the motors that rotate the color wheel. If the power to the light-fixtures is applied at the same instant, then each color wheel will begin stepping at the exact same time and the wheels will step at the same rate, being determined by the sine waves of the alternating—current source of power. Thus, the color wheels remain synchronized. 
     Referring to FIG. 7, which is an electrical scheme of the present embodiment of a synchronizer circuit  100  according to the present invention, the synchronizer circuit  100  includes a power supply circuit  120 , a filter  140 , a control circuit  160 , an index point sensing circuit  180 , and a low-impedance output driver circuit  200 . 
     A parts list for the synchronizer circuit  100  follows: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                  Reference 
                  Part Value 
                 Part Number 
                 Manufacturer 
               
               
                   
               
             
             
               
                  C1 
                    47 μF/35 V 
                 ECE-B1VFS470 
                 Panasonic 
               
               
                 C2 
                  100 μF/16 V 
                 ECE-A1CFS101 
                 Panasonic 
               
               
                 C3 
                  220 μF/10 V 
                 ECE-A1AFS221 
                 Panasonic 
               
               
                 C4 
                   1 nF 
                 ECU-V1H102KBM 
                 Panasonic 
               
               
                 D1, D2, D5, D6 
                 — 
                 DL4002 
                 Microsemi 
               
               
                 D3 
                 — 
                 DL4148 
                 Microsemi 
               
               
                 D4 
                 — 
                 SMB5817MS 
                 Microsemi 
               
               
                 L1 
                  330 μH 
                 5800-331 
                 J.W. Miller 
               
               
                 R1 
                  2.2 Ω 
                 — 
                 — 
               
               
                 R2, R3, R7 
                   68 kΩ 
                 ERJ-6GEYJ683 
                 Panasonic 
               
               
                 R4 
                  4.7 kΩ 
                 ERJ-6GEYJ472 
                 Panasonic 
               
               
                 R5, R6 
                   22 Ω 
                 — 
                 — 
               
               
                 U1 
                 — 
                 LM2574N-005 
                 Motorola 
               
               
                 U2, U6 
                 — 
                 TPS2813D 
                 Texas Instruments 
               
               
                 U3 
                 — 
                 A3144LU 
                 Allegro 
               
               
                 U4 
                 — 
                 PIC12C508-04I/P 
                 Microchip 
               
               
                 U5 
                 — 
                 MC33164P-3 
                 Motorola 
               
               
                   
               
             
          
         
       
     
     The power supply circuit  120  receives the alternating current supply voltage from the integral transformer  52  and provides a regulated 5 volt output  122 . In this particular embodiment, power supply  120  comprises a bridge rectifier including diodes D 1 , D 2 , D 5 , and D 6 , capacitor C 1 , and resistor R 1 . The rectified signal is provided to a step-down voltage regulator  126  that, in conjunction with diode D 4 , inductor L 1  and capacitor C 2 , regulates the output voltage to 5 V and filters unwanted frequency components of the regulated 5 V output  122 . When the alternating current supply voltage is not applied to the transformer, the output  122  goes to 0 volts. An uninterrupted 5 volt output  128  is also provided which continues to supply power for approximately 4 seconds, depending upon the load, after the alternating current supply voltage is interrupted. This power is stored in capacitor C 3  and when the supply power is interrupted the capacitor C 3  provides a limited supply of current at the output  128 . Diode D 3  is provided to prevent capacitor D 3  from being discharged by the power supply circuit  120 . 
     The filter  140  prevents unwanted high-frequency components of the alternating current supply voltage applied to it from passing to the control circuit  160 . The filter  140  comprises resistor R 2  and capacitor C 4  in a low-pass filter configuration. In addition, resistors R 2  and R 3  arranged in a voltage divider configuration reduce the voltage of the alternating current supply voltage passed to the control circuit  160 . 
     The index point sensing circuit  180  comprises the magnetic sensor  34  and resistor R 7 . When the magnetic index point  40  on the color wheel  36  is aligned with the sensor  34 , the sensor  34  outputs a logical “0” to input GP 2  of the microcontroller  170 ; otherwise GP 2  remains at 5 V. or logical “1”. One of skill in the art will appreciate that resistor R 7  is required for the present application of sensor  34  because sensor  34  has an open collector output. To this end, the resistor would normally connect the open collector output of sensor  34  to a positive 5 V supply to pull the output up. However, to prevent the sensor  34  from drawing power from microcontroller  170  when the alternating current supply voltage is interrupted, node GP 1  on the microcontroller  170  is programmed to provide 5 V to the resistor R 7  only when supply voltage is present. 
     The control circuit  160  comprises a reset circuit  162  and a microcontroller  170 . Reset circuit  162  provides a reset signal on its output that assists in resetting the microcontroller  170  when the alternating current supply-voltage is initially applied to the light fixture  10 . Reset circuit  162  comprises undervoltage sensor U 5  and resistor R 4 . 
     The low-impedance output driver circuit  200  comprises two dual high-speed MOSFET drivers U 2  and U 6 . The outputs of U 2  and U 6  are coupled to two coils, A and B, of the stepper motor  48  and provide sufficient current, in response to outputs from the microcontroller  170 , for driving the motor  48 . Power is provided to U 2  and U 6  from the 5 volt output  122 . 
     Coupled to the reset circuit  162 , the filter  140 , and the driver circuit  200  is the microcontroller  170 . The microcontroller  170  receives the reset signal provided by the reset circuit  162 , the alternating current supply voltage filtered by the filter  140 , and an index signal from the index point sensing circuit  180 . In response to these inputs, the microcontroller  170  provides control signals at outputs GP 4  and GP 5  in the form of a grey code to driver circuit  200 . The alternating current provided by filter  140  provides an input signal  190  for the microcontroller  170 . The microcontroller  170  is preprogrammed to provide control signals according to the following scheme. 
     In the initial state of the synchronizer circuit  100  there is no alternating current applied from the transformer  52  and no current stored in capacitor C 3 . When power is applied, the microcontroller  170  is placed in “state 0” and no control signals are provided to the driver circuit  200 , and thus the color wheel  36  remains stationary. To control the input signal  190 , a user must interrupt power provided to the transformer  52 . However, power must be reapplied within 4 seconds or capacitor C 3  will completely discharge, bringing the 5 volt output  128  to 0 volts and causing the reset circuit  162  to return the microcontroller  170  to “state 0. ” From “state 0, ” when input signal  190  is sequentially interrupted and reengaged (within 4 seconds), the microcontroller  70  is advanced to “state 1.” 
     Once placed in “state 1” the microcontroller  70  generates cycling outputs at GP 4  and GP 5  causing the driver circuit  200  to step the stepper motor  48  very quickly (“fast stepping”) until the microcontroller  170  receives a logical “0” input from the sensing circuit  180 . This positive input is caused by the alignment of the index point  40  with the magnetic sensor  34 . Once they are aligned, the controller waits for a predetermined period of time, t, and then the microcontroller  170  advances to “state 2. ” This predetermined period of time, t, allows any other lighting fixtures that are being synchronized using the same power source to become aligned, so that all of the lighting fixtures. The predetermined time, t, is selected in this embodiment to be twenty-one seconds, the time required for a full revolution of the color wheel during fast stepping of the motor  48 , twenty seconds, plus an additional second to account for the possibility of error. This is the longest possible time it should take to return the color wheel to alignment of the index point  40  with the sensor  34 . 
     In “state 2” the microcontroller generates slowly cycling outputs at GP 4  and GP 5  causing the driver circuit  200  to step the stepper motor  48  slowly (slow stepping), resulting in the color wheel  38  to rotate its color filters  42 ,  44  and  46  slowly past the lamps  18 , which will allow a user time to view each hue produced and make a selection. This slow stepping continues indefinitely until the input signal  190  is interrupted. From “state 2, ” when the input signal  190  is sequentially interrupted and reengaged (within 4 seconds), the microcontroller  170  returns to “state 0, ” and the color wheel  38  stops rotating. In this way, a user can choose a desired hue of light and cause the light fixture to halt. 
     The following table summarizes the control scheme described above: 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                  State 
                  Output 
                 Wait for 
                 and then 
               
               
                   
               
             
             
               
                  0 
                  none (stopped) 
                 “off” then “on” 
                 go to “state 1” 
               
               
                 1 
                 fast stepping to 
                 a predetermined 
                 go to “state 2” 
               
               
                   
                 index point and then stop 
                 period of time from 
               
               
                   
                   
                 last “on” 
               
               
                 2 
                 slow stepping 
                 “off” then “on” 
                 go to “state 0” 
               
               
                   
               
             
          
         
       
     
     As mentioned above, if at any time the power to transformer  52  is interrupted for longer than 4 seconds, the 5 volt output  128  will go to 0 volts and when reengaged, the microcontroller  170  will be reset to “state 0”. Thus, a user may select a position for the color wheels of one or more lighting fixtures that produces a desired hue of light and then turn off the lights at the source. When the source power is restored, the color wheels will remain stationary and the light will remain the chosen hue. Likewise, an unintentional interruption of source power, such as a power outage, will not cause the selected hue to change. 
     It should be appreciated that multiple light fixtures will step at precisely the same rate as long as they are connected to the same source of power. This is because the microcontroller  170  generates output signals at GP 4  and GP 5  that step a grey code to the driver circuit  200  once for every N sine wave transitions of the alternating current supply voltage. N is a number determined by the microcontroller  170  depending upon how quickly the stepper motor  48  must be advanced. For fast stepping N=1, which causes the color wheel  36  to make one full rotation every twenty seconds. For slow stepping N=6, causing the color wheel  36  to make one full rotation in 120 seconds. 
     Further, when synchronizing multiple light fixtures, one fixture may become misaligned with respect to the others if it its power is independently interrupted for some reason or if there is mechanical slippage. For this reason, a master reference pulse is generated by the microcontroller  170  by counting the number of alternating current transitions (120 transitions per second for a 60 Hz supply) after current is initially applied and generating a pulse every 120 seconds or 14,400 transitions, which is the normal (slow stepping) full rotation period. To correct the synchronization, the master reference pulse is compared to an index pulse received from the sensor  34 . The index pulse is generated every time the output of the sensor  34  is a logical “0”, indicating that the magnetic index point  40  is aligned with the sensor  34 . 
     If the master reference pulse is generated before the index pulse, then the microcontroller  170  determines that the color wheel  36  is lagging behind and the microcontroller  170  then begins to cause the motor to begin fast stepping until the index pulse is received from the sensor  34 . Since the fast stepping is 6 times faster than the slow stepping, the lag time will then be reduced by a factor of 6 for every complete rotation of the color wheel  36 . 
     If the index pulse is received before the master reference pulse is generated, then the microcontroller  170  determines that the color wheel  36  is ahead in its rotation and the microcontroller causes the color wheel  36  to stop rotating until the master reference pulse is generated. When the color wheel  36  resumes its rotation, it will be correctly aligned with the master reference pulse. 
     It should also be appreciated that, to conserve power, the sensor  34  and the driver circuit  200  are supplied power by 5 volt output  122 , instead of output  128 , so that when no power is being supplied by transformer  54  to power supply circuit  120 , the sensor  34  and the driver circuit  200  do not unnecessarily draw power from the capacitor C 3  and exhaust the limited supply of current from the capacitor C 3  too quickly.