Abstract:
A legacy-type fluorescent lamp fixture involves a magnetic ballast and a starter unit socket. Power savings are realized by using a retrofit fluorescent lamp assembly in place of the fluorescent lamp that would ordinarily by held in the fixture. The retrofit assembly may, for example, have a smaller fluorescent lamp. A digitally controlled electronic ballast within the retrofit assembly drives the smaller fluorescent lamp efficiently, thereby achieving power savings. In addition, an RF-enabled switch is installed in the starter unit socket. The RF-enabled switch communicates multi-bit digital control signals in serial fashion from the starter socket, through existing wires of the fixture, through the lamp holders of the fixture, and into the retrofit assembly. The electronic ballast receives these signals, decodes them, and in response turns on or turns off its lamp as commanded. Additional power savings are thereby achieved by keeping the lamp off when it is not needed.

Description:
TECHNICAL FIELD 
     The described embodiments relate to fluorescent lamp fixtures, to retrofit fluorescent lamp assemblies, and to associated methods. 
     BACKGROUND INFORMATION 
       FIG. 1  (Prior Art) is an exploded perspective view of an assembly involving one type of fluorescent lamp fixture referred to here as an old-fashioned or a “legacy” fluorescent lamp fixture.  FIG. 2  (Prior Art) is a circuit schematic of the assembly of  FIG. 1 . Legacy fixture  1  includes a base portion  2 , a transparent cover or lens  3 , and a starter unit  5 . Base portion  2  of the fixture includes a pair of T8 lamp holders  6  and  7 , a starter socket  8 , a magnetic ballast  9  that is disposed under a removable metal cover or tent  10 , and other parts not shown. A fluorescent lamp  4  is installed in the fixture. Fixture  1  receives AC power via electrical cord  11 . In one example, the fluorescent lamp  4  is a so-called T8 tubular fluorescent lamp having opposing G13 bi-pin bases  12  and  13 . The T8 lamp is installed in the fixture so that the two pins of G13 bi-pin base  12  fit into lamp holder  6  and make contact with two corresponding electrical contacts in lamp holder  6 . Similarly, the two pins of G13 bi-pin base  13  fit into lamp holder  7  and make contact with two corresponding electrical contacts in lamp holder  7 . When starter unit  5  is installed, the two terminals of the starter unit fit up and into corresponding holes in starter socket  8  and make electrical connections to two corresponding electrical contacts in the socket. 
     As is known in the art, a starter unit is required to turn on the lamp. In a first step, when AC power is applied to the fixture via cord  11 , a switch in starter unit  5  closes and forms an electrical connection between the filament  14  at one end of lamp  4  and the filament  15  at the other end of lamp  4 . An alternating current can then flow from an AC power source  16 , through inductive ballast  9 , through filament  14 , through the closed switch of the starter unit  5 , and through the second filament  15 , and back to the AC power source  16 . This flow of this current causes the filaments to heat. The heating of the filaments causes gas surrounding the filaments to ionize. Once the gas is ionized in this way, then the switch in the starter unit is opened. The opening of the switch cuts current flow through magnetic ballast  9 , thereby causing a large voltage spike to develop due to the inductive nature of the ballast. Due to the circuit topology, this large voltage is present between filaments  14  and  15 . The voltage is large enough to strike an arc between the filaments through the gas within the lamp. Once the arc is established, the resistance between the two filaments through the gas decreases. This allows current to continue to flow through the gas without a large voltage being present between the filaments. The switch of the starter unit is left open, the current continues to flow, filaments continue to be heated, the arc is maintained, and the magnitude of current flow is limited by the ballast. The fluorescent lamp is then said to be on. The arc generates UV light that then strikes a phosphor coating on the inside surface of the glass of the lamp. The phosphor coating captures energy of the UV light and reemits visible light. 
       FIG. 3  (Prior Art) is a circuit diagram of an assembly involving another type of fluorescent lamp fixture  20 . This type of fixture employs an electronic ballast  21 . Due to the operation of the electronic ballast, no separate starter unit is provided. Wires  23 - 26  and lamp holders  27  and  28  are parts of the fixture. Electronic ballast  21  receives 50-60 Hz AC power from AC source  16 , and then supplies a T8 fluorescent lamp  22  with an AC power signal having a higher frequency (for example, 20 kHz). Fluorescent lamps are generally more efficient in terms of converting electrical energy into visible light when they are driven at a higher frequency such as 20 kHz as opposed to when they are driven with an AC signal at 50-60 Hz. For these and other reasons, new fluorescent lamps fixtures are generally of the electronic ballast type. Legacy type fixtures as shown in  FIG. 1  still exist, but generally are older fixtures that have been installed and in use for some time. 
       FIG. 4  (Prior Art) is a circuit diagram of an assembly in which a so-called “T8-to-T5 retrofit assembly”  30  has been installed in a legacy fluorescent lamp fixture. The T8-to-T5 retrofit assembly  30  has the approximate form factor of an ordinary T8 fluorescent lamp. In this form factor, the T8-to-T5 retrofit assembly  30  provides two G13 bi-pin bases  31  and  32  mounted in opposing fashion as illustrated so that the T8-to-T5 retrofit assembly  30  can be installed in lamp holders  33  and  34  in place of a T8 lamp. In addition, retrofit assembly  30  includes an electronic ballast  35 , a T5 fluorescent lamp  36 , and two T5 lamp holders  37  and  38  configured to hold the T5 lamp. The electronic ballast  35  receives 50-60 Hz AC power from AC source  16 . A first conductive path extends from AC source  16 , through ballast  39 , through wire  40  of the legacy fixture, through contact  41  of lamp holder  33 , and into the T8-to-T5 retrofit assembly, and to a first power input of electronic ballast  35 . A second conductive path extends from AC source  16 , through wire  42  of the legacy fixture, through contact  43  of lamp holder  34 , into the T8-to-T5 retrofit assembly, through a short connection  44  within the retrofit assembly, back out of the T8-to-T5 retrofit assembly via contact  54  of lamp holder  34 , through wire  45  of the legacy fixture, through a dummy short  46  that is installed in starter socket  47 , through wire  48  of the legacy fixture, through contact  49  of lamp holder  33 , back into the retrofit assembly, and to a second power input of electronic ballast  35 . The electronic ballast receives AC power through these two conductive paths. The electronic ballast drives the T5 fluorescent lamp  36  via four conductors  50 - 53 . The existence of magnetic ballast  39  in the AC current path between AC source  16  and electronic ballast  35  does not interfere with operation of the electronic ballast. The magnetic ballast is of such an inductance that at the low 50-60 Hz frequency of the incoming AC power signal, the magnetic ballast has only a small impedance. By replacing a T8 lamp of a legacy fixture with such a T8-to-T5 retrofit assembly, power savings due to more efficient operation of the lamp can be realized. The fact that the smaller T5 lamp may output less light than the original larger T8 lamp is generally acceptable considering the improved efficiency gained. 
       FIG. 5  (Prior Art) is a circuit diagram of a proposed circuit whereby an owner of a legacy fixture  55  can achieve even more power savings as compared to using the circuit of  FIG. 4 . In the assembly of  FIG. 5 , an RF-enabled switch  56  is provided in the starter unit socket  57  of the legacy fixture. The internal wiring of the legacy fixture of the circuit of  FIG. 5  is identical to the internal wiring of the legacy fixture of  FIG. 1 . The T8-to-T5 retrofit assembly  61  of  FIG. 5  is identical to the T8-to-T5 retrofit assembly  30  of  FIG. 4 . The legacy fixture is generally a fixture that has been installed and used with T8 bulbs for many years, and is now being retrofitted to improve efficiency. 
     In the assembly of  FIG. 5 , the circuitry of the RF-enabled switch  56  receives power via existing conductors  58  and  59  of the legacy fixture. A switch in the RF-enabled switch  56  can be made to open in response to receiving an RF control signal  60 . If the switch is open, then power to the retrofit assembly  61  is cut off, lamp  62  is therefore off and is not powered. The switch in the RF-enabled switch  56  can also be made to close in response to receiving another RF control signal  63 . If the switch is closed, then power is supplied through the RF-enabled switch  56  and to the retrofit assembly  61 . The retrofit assembly  61  responds in standard fashion and drives lamp  62  so that lamp  62  is illuminated. By turning the lamp off when light is not needed, additional power savings can be realized in addition to the power savings achieved by simple use of the retrofit assembly. 
     In one example, the circuit of  FIG. 5  is installed in a room. A remotely located infra-red occupancy detector circuit (not shown) detects whether there are people in the room. If no people are detected and it is determined that light from lamp  62  is not needed, then the infra-red occupancy detector circuit transmits RF control signal  60  to the RF-enabled switch  56  thereby causing lamp  62  to be turned off. If, however, people are detected to be in the room, then the infra-red occupancy detector circuit may transmit RF control signal  63  to the RF-enabled switch  56  thereby causing lamp  62  to be turned on. By keeping the lamp  62  off when it is not needed, the circuit of  FIG. 5  achieves additional power savings as compared to the circuit of  FIG. 4 . 
     SUMMARY 
     A legacy-type fluorescent lamp fixture involves a magnetic ballast and a starter unit socket. Rather than a fluorescent lamp being held between two fluorescent lamp holders of the fixture in conventional fashion, a novel retrofit fluorescent lamp assembly is installed in place of the fluorescent lamp. The retrofit fluorescent lamp assembly is held by the two fluorescent lamp holders in the same way that an ordinary fluorescent lamp would have been held. In addition, an RF-enabled switch is installed in the starter socket of the fixture. AC power from an AC power source (for example, 120 VAC @ 60 Hz wall power or 240 VAC @ 50 Hz wall power) is received onto the retrofit fluorescent lamp assembly via two conductive paths and is used to power a lamp of the retrofit fluorescent lamp assembly. A first conductive path extends from the AC power source, through the magnetic ballast, through a first contact of a first lamp holder, through a first pin of a first bi-pin base of the retrofit fluorescent lamp assembly, and to a first AC power input of a digitally controllable electronic ballast of the retrofit fluorescent lamp assembly. A second conductive path extends from the AC power source, through a first contact of a second lamp holder, through a first pin of a second bi-pin base of the retrofit fluorescent lamp assembly, and to a second AC power input of the digitally controllable electronic ballast of the retrofit fluorescent lamp assembly. The other two pins of the bi-pin bases of the retrofit fluorescent lamp assembly, namely the second pin of the first bi-pin base and the second pin of the second bi-pin base, are used to communicate multi-bit digital control signals between the starter socket and the retrofit fluorescent lamp assembly. A pair of preexisting wires of the legacy type fixture extend from these second pins of the bi-pin bases to the two contacts of the starter socket. No changing of the wiring of the legacy type fixture is required to accommodate the retrofit assembly and the RF-enabled switch in this way. 
     In one specific example, a remotely located infra-red occupancy detector and the fixture are disposed in a room to be illuminated. The occupancy detector determines that the room is occupied and that the lamp of the fixture should be illuminated. The occupancy detector therefore transmits a first RF signal to the RF-enabled switch. In response, the RF-enabled switch sends a first multi-bit digital control signal out of the starter socket and via the second pin of the second bi-pin base of the retrofit assembly into the retrofit lamp assembly and to the digitally controllable electronic ballast of the retrofit assembly. The digitally controllable electronic ballast decodes the first multi-bit digital control signal and in response turns on the lamp of the retrofit assembly. In another example, the occupancy detector determines that the room is vacant. The occupancy detector therefore transmits a second RF signal to the RF-enabled switch. In response, the RF-enabled switch sends a second multi-bit digital control signal out of the starter socket and via the second pin of the second bi-pin base of the retrofit assembly into the retrofit lamp assembly and to the digitally controllable electronic ballast. The digitally controllable electronic ballast decodes the second multi-bit digital control signal and in response turns off the lamp. The first pins of the first and second bi-pin bases of the retrofit assembly are used to receive AC power onto the retrofit assembly. These two pins are not used to communicate the multi-bit digital control signals. The second pins of the first and second bi-pin bases of the retrofit assembly are used to communicate the multi-bit digital control signals and are not used to receive AC power onto the retrofit assembly. 
     In one specific example, the retrofit assembly sources a DC voltage through a resistance. This DC voltage is sourced out of the second pins of the first and second bi-pin bases. The DC voltage is present between the second pins of the first and second bi-pin bases provided that a switch of the RF-enabled switch is not closed and coupling the second pins of the first and second bi-pin bases together. Circuitry of the RF-enabled switch is powered by this DC voltage. If the switch of the RF-enabled switch is closed and coupling the second pins of the first and second bi-pin bases together, then the voltage on the second pin of the second bi-pin base is pulled down toward ground potential (ground potential is present on the second pin of the first bi-pin base) through the sourcing resistance. The changing voltage levels on the second pin of the second bi-pin base as the switch of the RF-enabled switch is opened and closed are detected by the digitally controllable ballast as the multi-bit digital signal. The overall assembly involving the legacy-type fluorescent lamp fixture, the novel retrofit lamp assembly, the lamp held by the retrofit lamp assembly, and the RF-enabled switch promotes power savings in driving the lamp, as compared to driving a lamp with a conventional retrofit lamp assembly, both: 1) due to driving the lamp of the retrofit assembly efficiently when the lamp is on, and 2) due to turning the lamp off when light from the lamp is not needed. These savings can be achieved with a legacy-type fluorescent lamp fixture without making any modifications to the wiring of the fixture itself. All that is required is the replacement of the conventional fluorescent lamp with the novel retrofit assembly and the installation of a suitable controllable switch (for example, the RF-enabled switch) in the starter socket of the fixture. Although in some embodiments the retrofit assembly holds and powers a fluorescent lamp as described above, in other embodiments the retrofit assembly holds and powers another type of lighting element such as, for example, an LED light emitting element or an incandescent light emitting element. Although an RF-enabled switch is described as one way of injecting digital signals into the retrofit assembly via the starter socket, other circuits and digital signaling schemes can be employed to communicate digital signals with the retrofit assembly using the starter socket as a communication port. Digital communication through the starter socket can be bidirectional. 
     Further details and embodiments and techniques and methods are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG. 1  (Prior Art) is an exploded perspective view of an assembly involving a legacy fluorescent lamp fixture having a magnetic ballast and a starter socket. 
         FIG. 2  (Prior Art) is a circuit schematic of the assembly of  FIG. 1 . 
         FIG. 3  (Prior Art) is a circuit diagram of an assembly involving a type of fluorescent lamp fixture having an electronic ballast. 
         FIG. 4  (Prior Art) is a circuit diagram of an assembly in which a retrofit assembly has been installed in a legacy fluorescent lamp fixture. 
         FIG. 5  (Prior Art) is a circuit diagram of a proposed circuit. 
         FIG. 6  is a diagram of an assembly  65  in accordance with one novel aspect. The assembly  65  involves a novel retrofit fluorescent lamp assembly and an RF-enabled switch that are installed in a legacy fixture. 
         FIG. 7  is a circuit diagram showing the digitally controllable electronic ballast of the retrofit assembly of  FIG. 6  in further detail. 
         FIG. 8  is a perspective view of the leftmost end of the retrofit assembly of  FIG. 6 . 
         FIG. 9  is an end view looking into the contacts of one of the bi-pin T8 fluorescent lamp holders of  FIG. 6 . 
         FIG. 10  is a side view of the leftmost G5 bi-pin base of the T5 fluorescent lamp  99  that is mounted in the retrofit assembly of  FIG. 6 . 
         FIG. 11  is an end view of the G5 bi-pin base of  FIG. 10 . 
         FIG. 12  is a perspective view of the RF-enabled switch of  FIG. 6 . 
         FIG. 13  is an exploded view of the RF-enabled switch of  FIG. 6 . 
         FIG. 14  is a flowchart of a method  200  in accordance with one novel aspect. 
         FIG. 15  is a flowchart of a method  300  in accordance with one novel aspect. 
         FIG. 16  is a flowchart of a method  400  in accordance with one novel aspect. 
         FIG. 17  is a flowchart of a method  500  in accordance with one novel aspect. 
         FIG. 18  is a flowchart of a method  600  in accordance with one novel aspect. 
     
    
    
     DETAILED DESCRIPTION 
     The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
       FIG. 6  is a diagram of an assembly  65  in accordance with one novel aspect. Overall assembly  65  includes a RF-communicating remote device  66  (such as an infra-red occupancy detector having an RF communicating capability), an AC power source  67 , a light fixture  68 , a novel T8-to-T5 retrofit assembly  69 , and a novel RF-enabled switch  70 . Light fixture  68  is a legacy-type fluorescent lamp fixture that includes a magnetic ballast  71 , a starter socket  72  for accommodating a conventional starter unit, two T8 lamp holders  73  and  74  positioned to hold a T8 fluorescent lamp, and associated wires or connections  64 ,  75 ,  76 ,  77  and  78 . The legacy fixture  68  is identical to the legacy fixture  1  of  FIG. 1  and includes a base portion, a removable cover for the ballast, and a transparent cover or lens as pictured in  FIG. 1 . The legacy fixture can take on many different forms. The form of  FIG. 1  is just one example. 
     Rather than a T8 fluorescent lamp being installed in conventional fashion in the T8 lamp holders  73  and  74 , the novel T8-to-T5 retrofit assembly  69  is installed in the place of the T8 fluorescent lamp. Pins  79  and  80  of a first G13 bi-pin base  81  of the retrofit assembly make electrical contact with corresponding electrical contacts  82  and  83  of T8 lamp holder  73 , respectively. Similarly, pins  84  and  85  of a second G13 bi-pin base  86  of the retrofit assembly make electrical contact with corresponding electrical contacts  87  and  88  of T8 lamp holder  74 , respectively. The novel T8-to-T5 retrofit assembly  69  includes the two G13 bi-pins bases  81  and  86 , a supporting base member  130 , a novel digitally controllable electronic ballast  141 , wires or connections  89 - 96 , and two T5 lamp holders  97  and  98 . A T5 fluorescent lamp  99  is installed in the retrofit assembly so that it is held by T5 lamp holders  97  and  98 . The bi-pin bases  81  and  86  and ballast  141  are mounted to the base member  130 . All these components are interconnected as illustrated in  FIG. 6 . 
     The novel digitally controlled electronic ballast  141 , along with its associated wiring, properly interconnected, is an example of what is referred to here as a lamp drive circuit. The digitally controllable electronic ballast  141  drives leftmost filament  100  via wire or conductor  91 , contact  101 , a first pin of the leftmost G5 bi-pin base of the T5 lamp  99 , the filament  100 , a second pin of the leftmost G5 bi-pin base of the T5 lamp  99 , contact  102 , and wire or conductor  92 . Digitally controllable electronic ballast  141  drives filament  103  via wire or conductor  93 , contact  104 , a first pin of the rightmost G5 bi-pin base of the T5 lamp  99 , the filament  103 , a second pin of the rightmost G5 bi-pin base of the T5 lamp  99 , contact  105 , and wire or conductor  94 . 
     Rather than the RF-enabled switch trying to turn on and off the lamp by supplying AC power or not supplying AC power to the retrofit assembly as in the proposed circuit of  FIG. 5 , AC power for the retrofit assembly does not pass through RF-enabled switch  70 . Heating problems and reliability problems are avoided by not conducting high currents through switch  70 . Switch  70  is therefore made less expensively. To accomplish this, one of the pins  79  of G13 bi-pin base  81  is coupled by wire or conductor  89  to a first power input of electronic ballast  141  and one of the pins  84  of G13 bi-pin base  86  is coupled by wire or conductor  90  to a second power input of electronic ballast  141 . AC power to the retrofit assembly  69  therefore can be supplied by the fixture and to the retrofit assembly  69  without the AC power that drives the lamp  99  flowing through pins  80  and  85 , through wires or conductors  76  and  77 , through starter socket  72 , or through RF-enabled switch  70 . Within retrofit assembly  69 , pin  80  of G13 bi-pin base  81  is coupled by wire or conductor  95  to a first digital signal input of electronic ballast  141 , and pin  85  of G13 bi-pin base  86  is coupled by wire or conductor  96  to a second digital signal input of electronic ballast  141 . Pins  80  and  85  are not needed to supply AC power to the retrofit assembly. In the example of  FIG. 6 , pins  80  and  85  are used: 1) to supply a relatively small amount of power from retrofit assembly  69  to RF-enabled switch  70  to power circuitry in switch  70 , and 2) to receive multi-bit digital control signals  106  and  107  from RF-enabled switch  70 . The multi-bit digital control signals  106  and  107  are communicated in serial fashion from RF-enabled switch  70 , through a contact of starter socket  72 , through wire or conductor  77 , through contact  88  of lamp holder  74 , through pin  85  of G13 bi-pin base  86  of the retrofit assembly, through wire or conductor  96  to the second digital signal input of electronic ballast  141 . Wire or conductor  76  in this example is used as a ground connection, both for power purposes and for signaling purposes. Wires or conductors  76  and  77  are pre-existing wires or conductors of the legacy fixture. No changing of the wiring of the legacy fixture is required to provide the communication path for communicating multi-bit digital control signals between socket  72  and electronic ballast  141 . 
     In one example, remote infra-red occupancy detector  66  detects motion and determines that lamp  99  is to be turned on. It therefore transmits an RF control signal  108  to RF-enabled switch  70 . RF-enabled switch  70  in turn sends multi-bit digital control signal  106  through socket  72  and wire or connection  77  to the digitally controlled electronic ballast  141 . The digitally controlled electronic ballast  141  receives the multi-bit digital control signal  106 , decodes the multi-bit digital control signal and determines that the signal is an ON command, and in response turns lamp  99  on. Later, remote infra-red occupancy detector  66  determines that lamp  99  is to be turned off. This may, for example, be due to the occupancy detector not detecting motion for a period of time. Occupancy detector  66  transmits an RF control signal  109  to RF-enabled switch  70 . RF-enabled switch  70  in turn sends multi-bit digital control signal  107  through socket  72  and wire or connection  77  to the digitally controlled electronic ballast  141 . The digitally controlled electronic ballast  141  receives the multi-bit digital control signal  107 , decodes the signal and determines that the signal is an OFF command, and in response turns off lamp  99 . Occupancy detector  66  can cause lamp  99  to be turned on and turned off in this way. 
     Although in this illustrated example the communication path through the starter socket  72  is used to communicate ON and OFF commands in unidirectional fashion, in other examples the communication path between starter socket  72  and the ballast  141  is usable to communicate other digital information and other commands, both into the retrofit assembly and/or out of the retrofit assembly. One of many different serial protocols and error detecting schemes can be used. RF-enabled switch  70  is but one way of communicating multi-bit digital signals through socket  72 . A circuit other than an RF-enabled switch can be employed for this purpose. The circuit that communicates signals through the socket need not be RF-enabled, and need not have the form factor of a starter unit. Although single-ended signaling is described in the example of  FIG. 6  as the way that the multi-bit digital signals are communicated, differential signaling may be employed to communicate the multi-bit digital signals in other examples. Although power is supplied through the socket  72  in the example of  FIG. 6  to power RF-enabled switch  70 , in other examples the circuit that communicates through socket  72  is not powered through the socket. Although the retrofit assembly  69  involves driving a fluorescent lamp in the example of  FIG. 6 , the retrofit assembly in other examples may have other functions. In one example, the retrofit assembly does not power a fluorescent lamp, but rather has a lighting element involving LEDs (Light Emitting Diodes). Power electronics for supplying the proper supply voltage to the LEDs receives AC power through pins  79  and  84 , whereas the other pins  80  and  85  of the retrofit assembly are used to send and/or to receive digital signals to/from the retrofit assembly via existing wires  76  and  77  and socket  72 . 
       FIG. 7  is a more detailed diagram of one specific example of the digitally controlled electronic ballast  141  of  FIG. 6 . Ballast  141  includes an EMI filter  110 , a rectifier stage  111 , a DC boost supply stage  112 , a lamp control bridge stage  113 , and digital control signal communication circuitry  114 . Rectifier stage  111  converts 85 VAC to 250 VAC incoming AC wall power into a rectified DC supply voltage of a corresponding magnitude of 120 VDC to 353 VDC. DC boost supply stage  112  is a DC-to-DC switching power supply that converts the 120 volt to 353 volt DC supply voltage from the rectifier stage into a DC supply voltage of a higher voltage such as, for example, 400 volts DC. Lamp control bridge  113  switches the 400 volt DC signal onto the contacts of the T5 lamp holders as appropriate to drive the T5 fluorescent lamp. The composition and design of stages  110 - 113  are understood by those of skill in the art. There are variations of the circuitry that can be used in the various stages. Often several or all of the stages are provided with digital on/off control so that the various stages can be powered up and/or down in a particular sequence. In the example of  FIG. 7 , digital control signal communication circuitry  114  uses the on/off control mechanisms of the stages to turn on and to turn off lamp  99 . A low output power linear regulator  115  converts a larger voltage DC supply voltage as output by rectifier stage  111  into a regulated 5.0 volt DC supply voltage on voltage supply conductor  116 . Bypass and storage capacitor  117  is coupled between supply conductor  116  and ground conductor  118  across the outputs of the linear regulator. The 5.0 volt DC supply voltage output by the linear regulator powers a voltage reference circuit  119 , a comparator  120 , and a digital control circuit  121 . The 5.0 volt DC signal is also sourced out of the retrofit assembly onto pin  85  through resistor  123 . If switch  122  in RF-enabled switch  70  is open, then there is no voltage drop across resistor  123  and 5.0 volt DC is present on wire or conductor  96 . If, on the other hand, the switch  122  in RF-enabled switch  70  is closed then the voltage on wire or conductor  96  is lower than 5.0 volts DC. Signaling voltages are relative to the voltage on wire or conductor  95 . The state of switch  122  in the RF-enabled switch  70  therefore controls the voltage on the non-inverting input lead of comparator  120 . Comparator  120  compares the voltage on its non-inverting input lead to a reference voltage. The reference voltage is supplied by voltage reference circuit  119  onto the inverting input lead of comparator  120 . Comparator  120  outputs a digital signal  124  indicative of the state of switch  122 . Digital control circuit  121  (which may be a microcontroller) receives digital signal  124 , deserializes and decodes it to determine its information content, and then turns on or off lamp  99  as appropriate by sending ON/OFF digital controls signals to one or more of the stages  111 - 113  via one or more of conductors  125 - 127 . Reference numerals  128  and  129  identify contacts in the starter socket  72  that are coupled to wires or conductors  76  and  77 , respectively. 
       FIG. 8  is a perspective view of the leftmost end of the T8-to-T5 retrofit assembly  69  of  FIG. 6 . 
       FIG. 9  is an end view looking into the contacts of the bi-pin T8 fluorescent lamp holder  73  of the legacy fixture of  FIG. 6 . An end view looking into the contacts of the bi-pin T5 fluorescent lamp holder  97  of the retrofit assembly is similar but it is a smaller dimension to accommodate the smaller pin spacing between the bi-pins of a T5 lamp. 
       FIG. 10  is a side view of the leftmost G5 bi-pin base of the T5 fluorescent lamp  99  of the retrofit assembly of  FIG. 6 . 
       FIG. 11  is an end view of the G5 bi-pin base of  FIG. 10 . 
       FIG. 12  is a perspective view of the RF-enabled switch  70  of  FIG. 6 . 
       FIG. 13  is an exploded view of the RF-enabled switch  70  of  FIG. 6 . RF enabled switch  70  includes a plastic cap  131  through which propagating RF electromagnetic signals can pass, a printed circuit board  132 , and terminals  133  and  134 . Terminals  133  and  134  of RF-enabled switch  70  are positioned to make electrical contact with contacts  128  and  129  of socket  72 . Circuitry on the printed circuit board  132  includes switch  122 , a power supply  135 , a microcontroller  136 , an RF transceiver  137 , an antenna  138 , and other components. Power supply  135  receives power from terminals  133  and  134  (due to ballast  141  supplying 5.0 volt DC between wires  76  and  77 ), generates a regulated DC supply voltage, and supplies the regulated DC supply voltage to microcontroller  136  and to transceiver  137 . Microcontroller  136  controls the state of switch  122  via one of the signal lines  139 . Microcontroller  136  communicates wirelessly via signal lines  140 , RF transceiver  137  and antenna  138 . For additional background information on such an RF-enabled switch, see: U.S. patent application Ser. No. 12/803,308, entitled “Alternating Turn Off Timing Of A Fluorescent Lamp Starter Unit”, filed Jun. 22, 2010, by Tran et al. (the entire contents of which is incorporated herein by reference). Rather than controlling switch  122  to turn off and to turn on a fluorescent lamp directly as described in application Ser. No. 12/803,308, the switch  122  in the circuit of  FIG. 7  is turned off and on by the same microcontroller controlled mechanism but the turning on and off of switch  122  modulates digital information in serial fashion onto wire  77  of  FIG. 7 . Wire  76  is considered to carry a relative ground potential for the signal on wire  77 . 
       FIG. 14  is a flowchart of a method  200  in accordance with one novel aspect. A multi-bit digital signal is received (step  201 ) in serial fashion onto a contact of a fluorescent lamp holder. 
       FIG. 15  is a flowchart of a method  300  in accordance with one novel aspect. A multi-bit digital signal is received (step  301 ) in serial fashion onto a pin of a fluorescent lamp base. 
       FIG. 16  is a flowchart of a method  400  in accordance with one novel aspect. A multi-bit digital signal is sent (step  401 ) in serial fashion out of a contact of a fluorescent lamp holder. 
       FIG. 17  is a flowchart of a method  500  in accordance with one novel aspect. A multi-bit digital signal is sent (step  501 ) in serial fashion out of a pin of a fluorescent lamp base. 
       FIG. 18  is a flowchart of a method  600  in accordance with one novel aspect. Power is supplied (step  601 ) to a circuit via two conductive paths. In one example, a first conductive path extends from a first bi-pin fluorescent lamp base pin, through a first fluorescent lamp holder contact, through a first contact of a starter unit socket, and to the circuit. A second conductive path extends from a second bi-pin fluorescent lamp base pin, through a second fluorescent lamp holder contact, through a second contact of the starter unit socket, and to the circuit. A multi-bit digital signal is received (step  602 ) in serial fashion from the circuit via at least one of the two conductive paths. In response to the multi-bit digital signal, a corresponding indicated action is performed (step  603 ). The action corresponds to a value of the multi-bit digital signal. In one example of the method  600 , the supplying of step  601 , the receiving of step  602 , and the performing of step  603  are performed by the T8-to-T5 retrofit assembly  68  of  FIG. 6 . 
     Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Although embodiments are described above in which the legacy fixture has T8 lamp holders, the legacy fixture into which the novel retrofit assembly and RF-enabled switch are installed may have fluorescent lamp holders of another type or another size. The legacy fixture may be fashioned to hold any one of many different styles and types of fluorescent lamps. The novel retrofit assembly may likewise be of an appropriate form factor and may have suitable connections so that the retrofit assembly can be used in place of any such fluorescent lamp. Although an embodiment of the novel retrofit assembly is described above in which the lighting element of the retrofit assembly is removable and is a fluorescent lamp, the lighting element of the retrofit assembly in some embodiments is not be removable and is not a fluorescent lamp. Moreover, the use of an existing starter socket of a legacy fixture as a communication port through which multi-bit digital control information is communicated into and/or out of the fixture in serial fashion is not limited to use with a retrofit assembly. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.