Abstract:
An apparatus and method for cycling power to a HID ballast and amp in order to reduce the possibility of arc tube rupture or non-passive end of life light source failure with a warning indicator indicating impending momentary power outage. The apparatus comprises a lamp, a ballast, and a microcontroller operable to generate a warning indicator after expiration of a pre-selected period of time. The warning indicator indicates termination of power to the lamp for a predetermined period of time, by alternatively dimming and increasing the light output of the lamp. After expiration of the pre-determined period of time, the microcontroller restores the power to the ballast. The above described process is repeated periodically in order to reduce the risk of arc tube rupture.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a system and method that cycles a luminaire, such as one containing a metal-halide lamp, on and off at designated intervals in order to reduce the risk of arc tube rupture. More particularly, the present invention relates to a system and method that repeatedly switches the lamp from a high to low power output state before causing the lamp to extinguish, for a brief period of time, in order to provide a warning to anyone in the general vicinity of the luminaire that the lamp is about to be extinguished.  
         BACKGROUND OF THE INVENTION  
         [0002]    High intensity discharge (HID) lamps such as metal halide (MH) and high pressure sodium (HPS) lamps have increasingly gained acceptance over incandescent and fluorescent lamps for commercial and industrial applications. HID lamps are more efficient and more cost effective than incandescent and fluorescent lamps for illuminating large open spaces such as construction sites, stadiums, parking lots, warehouses, and so on, as well as for illumination along roadways. An HID lamp comprises an arc-tube containing at least two electrodes, chemical compounds and a fill gas. The fill gas can comprise one or more gases. To initiate operation of the lamp, the fill gas is ionized to facilitate the conduction of electricity between the electrodes. However, these light sources have been found to be susceptible to non-passive lamp failure, or, arc tube rupture.  
           [0003]    Non-passive lamp failures generally occur in response to crack propagation of the associated arc tube. Specifically, when the internal arc tube ages and develops minute faults, the arc tube may fracture allowing high pressure to force hot arc tube fragments through the outer glass jacket. If the associated luminaire is not suitably enclosed, falling arc tube fragments may pose a danger to personnel and property. Many luminaires are not enclosed, and accordingly, non-passive end-of-life light source failure is of concern to lamp and luminaire manufacturers.  
           [0004]    To prevent the above described situations, high intensity discharge lamp manufacturers recommend periodic cycling of lamps. Where lamps are used in applications that run continuously, lamp manufacturers require regular cycling, typically once a week. In operation, the high wattage light source such as, for example a HID lamp, is periodically cycled off and then back on. As mentioned above, an arc tube that has developed a weakness will most likely fail passively during the cool down and possibly the subsequent warm up cycle. To accomplish the required cycling of these lamps, the lamps should be de-energized and re-energized, per the lamp manufacturer&#39;s recommendations.  
           [0005]    Accordingly, an end user could extinguish the lighting from the panel-board on a regular basis, for example, weekly, but there are two flaws in using this method. First, an end user that would operate a facility 24 hours a day/seven days a week would most likely not want to monitor the lighting and whether or not it had been cycled once a week. Secondly, if the end user were to de-energize the luminaire from the panel-board many luminaires would be off at once, probably in the same area, which could become a separate safety issue, in addition to the arc tube failure mentioned above. Although individual timers could be attached to each circuit such an arrangement is a cumbersome solution.  
           [0006]    A proposed solution is found in U.S. Pat. No. 6,247,187 to Green, entitled “System for Promoting Passive End of Life Light Source Failure.” The Green patent discloses a system which automatically energizes and de-energizes a HID light source, however, no warning system is given of the impending power outage. In many applications the lamps are running continuously and an unexpected power outage could be extremely dangerous. For example, suppose a lift truck operator is 15 feet above the ground, for instance in a warehouse environment, and suddenly the luminaire that they are working under goes dark, the operator can experience momentary disorientation or severe enough confusion that could lead to an unfortunate accident.  
           [0007]    Accordingly, a need exists for a warning sequence before a luminaire is cycled off to prevent arc tube failure. The high to low cycling of the lamp is much subtler than an abrupt shutdown of the luminaire and would warn people in the area so that they could prepare mentally and physically for the upcoming outage.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a luminaire assembly that comprises a warning sequence before the luminaire de-energizes and energizes in order to reduce the risk of non-passive end of life failure or arc tube rupture.  
           [0009]    It is a further object of the present invention to have a self-contained, relatively small circuit that allows the warning function to be retrofit into a conventional metal-halide lamp.  
           [0010]    It is yet a further object of the present invention to provide a luminaire assembly that is able to withstand high instantaneous power level changes.  
           [0011]    It is still a further object of the present invention to provide a luminaire assembly with a warning feature as well as ae cycling feature for a HID lamp employing either a constant wattage ballast or a magnetically regulated ballast.  
           [0012]    These and other objects are substantially achieved by a luminaire assembly comprising a lamp, a ballast, and a microcontroller circuit operable to generate a warning indicator after expiration of a pre-selected period of time. The warning indicator indicates the impending termination of power to the lamp for a pre-determined period of time. Upon expiration of the pre-determined period of time, the microcontroller then restores the power to the lamp and resets the internal timing function. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    These and other aspects, advantages and novel features of the invention will be more readily appreciated from the following detailed description when read in conjunction with the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a first embodiment of a HID luminaire employing a parallel capacitive relay contact arrangement constructed in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a second embodiment of a HID luminaire employing a series resistive and bypass relay contact arrangement coupled to the primary winding of a ballast constructed in accordance with an embodiment of the present invention;  
         [0016]    [0016]FIG. 3 is an additional embodiment of a HID luminaire employing a series resistive and bypass relay contact arrangement coupled to the secondary winding of a ballast constructed in accordance with an embodiment of the present invention; and  
         [0017]    [0017]FIG. 4 is another embodiment of a HID luminaire employing a magnetically regulated ballast and a series resistive and bypass relay contact arrangement constructed in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    [0018]FIG. 1 depicts the ballast circuit  10  provided in accordance with an embodiment of the present invention. The ballast circuit  10  is employed with a metal halide lamp  12  to cycle power via relay contact  14  thus promoting passive end of life light source failure. In addition, the ballast circuit  10  employs an additional relay contact  16  which by action gives anyone in the vicinity of the light source a warning of the impending power outage, via a momentary high to low cycling of the lamp power. The high to low cycling of the lamp  12  is much subtler than an abrupt shutdown and would warn people in the area so that they could prepare mentally and physically for the upcoming outage.  
         [0019]    The ballast circuit  10  comprises a power source  11 , a conventional constant-wattage ballast  18 , described in detail below, two single-pole normally closed relay contacts  14  and  16  controlled by a microcontroller  20 , to achieve temporary removal of power as well as the warning indicator, as mentioned above.  
         [0020]    The starting and operating characteristics of HID lamps require the lamps to be operated from a ballast which limits the lamp operating current and wattage. One common type of ballast employed to operate HID lamps is a constant wattage autotransformer ballast  18  comprising a magnetic core  30  having two windings, a primary winding  26  and a secondary winding  28  coupled to series capacitors  22  and  24 , and a 120 Volt tap  19 .  
         [0021]    In the first embodiment of the present invention, the ballast circuit  10  employs a constant-wattage autotransformer ballast  18 , as detailed above. However, as discussed further below, a magnetically regulated ballast is also employed in an additional embodiment of the present invention. A capacitor  22  is serially coupled to the secondary winding  28 , along with a parallel capacitor  24  (C p ) and relay contact  16 . The lamp  12  is connected across the ballast  18  and coupled serially to parallel capacitors  22  and  24 .  
         [0022]    Turning to the operation of the ballast circuit  10 , the microcontroller  20  is typically programmed to act as a weeklong timer that performs two different functions at the end of the timing cycle. First, for the purpose of safety, it causes the lamp  12  to switch repeatedly from high to low to high for a pre-set period of time in an effort to communicate to anyone in the vicinity that the lamp is about to be extinguished. The switching is accomplished by relay contact  16 , which is controlled by microcontroller  20 . It should also be noted that the microcontroller  20  is programmable to set the timing cycle to any desired length.  
         [0023]    In order to operate the lamp in a reduced power mode from a magnetic ballast  18 , the ballast circuit  10  is employed to effect a power reduction provided by the ballast to the lamp. As mentioned above, one type of ballast commonly employed to operate HID lamps is the constant wattage auto-transformer  18  where the two windings  26  and  28  and the core  30  are capacitively coupled to the lamp via capacitors  22  and  24 .  
         [0024]    The high to low cycling of the lamp  12  is accomplished via the parallel capacitors  22  and  24  and relay contact  16  which alters the net impedance of the ballast  18 . Altering the impedance of the ballast  18  effects a change in the power provided to the lamp  12  which thereby effects a change in the luminaire provided by the lamp  12 . Specifically, the capacitance of the parallel combination of capacitors  22  and  24  is at a higher value of either capacitor alone. Accordingly, together with the primary winding  26  and secondary winding  28  this parallel capacitance created by capacitors  22  and  24  enables a higher current to be supplied to lamp  12 , thereby causing it to operate at a normal energy consumption level or in its full light mode.  
         [0025]    Relay contact  16  is activated by microcontroller  20  causing an open circuit condition and removing capacitor  24  from the circuit. Accordingly, capacitor  22  together with the primary winding  26  and secondary winding  28  of ballast  18 , however without capacitor  24 , supply lamp  12  with substantially lower levels of current to produce a reduced light output from lamp  12 . The lamp operates in this mode until the relay contact  16  is activated by microcontroller  20  to put the conditions back into full energy consumption mode again. Accordingly, the microcontroller  20  operates the relay contact  16  in an alternating sequence such that to those in the vicinity it would appear that the lights dim and brighten repeatedly for a pre-determined period of time.  
         [0026]    After the above described series of events has occurred, the microcontroller  20  interrupts the power supply  11  connection to the ballast  18  via relay contact  14  thus causing the lamp  12  to extinguish. The microcontroller  20  resets since the voltage source  11  is momentarily disconnected from the ballast  18  thus removing voltage from the microcontroller  20 , via the 120 Volt tap  19 . Upon closure of relay contact  14  the power supply  11  is again connected to the ballast  18  and microcontroller  20 , and the lamp will restart after it cools, beginning the process over again. In the event that the power is interrupted during the timing cycle, the microcontroller  20  resets and proceeds as if from time zero. That is, the microcontroller  20  begins timing the week, for example, from the time the power is restored. Typically, if the microcontroller  20  loses power on a Thursday, and power is restored on Thursday, the microcontroller  20  now cycles the lamp  12  on each successive Thursday, despite the original timing being set for cycling each Saturday. The Saturday cycle schedule can be reacquired manually, however, by momentarily interrupting the supply  11  at, for example, 10 A.M. Saturday, if desired.  
         [0027]    Accordingly, as long as the lamp  12  is cycled once a week, not on any particular day, this satisfies all of the safety recommendations currently being made by manufacturers of metal halide lamps. If this system were a standard 400 Watt metal-halide lamp, then an appropriate value for capacitor  24  is 7.0 microfarads to complement the series capacitor having a value of 17.0 microfarads.  
         [0028]    [0028]FIG. 2 is illustrative of an additional embodiment of the present invention. In this case, the microcontroller  20  controls the normally closed relay contacts  14  and  16  as in the first embodiment of the present invention, as detailed above. However, in this additional embodiment, the relay contact  16  is placed across a series resistor  32  which is in turn coupled to the primary winding  26  of the ballast  18 . Additionally, the relay contact  14  is used to interrupt the power being drawn by the ballast  23  thus causing the lamp  12  to extinguish, via the 120 Volt tap  19 . Specifically, when the relay contact  16  is cycled from closed to open, the resistor  32  is placed in series with the primary winding  26  of ballast  18  reducing the effective supply voltage available to the ballast  23 . This, in turn, reduces the power delivered to the lamp  12  and causes the lamp&#39;s luminous output to drop. The opening and closing of the relay contact  16  continues for a period of time causing the lamp  12  to dim and brighten, in an alternating fashion, as described in connection with FIG. 1. The increasing and decreasing light output is adequate to indicate that the lamp  12  is soon to be extinguished. Additionally, relay contact  14  serves the same function as described in connection with FIG. 1. That is, upon expiration of the warning indicator, or high and low cycling of the lamp  12  output, via relay contact  16 , microcontroller  20  activates the normally closed relay contact  14  to interrupt power to the lamp  12  for an adequate amount of time to allow the lamp to extinguish.  
         [0029]    It is important to note that an advantage of an embodiment of the present invention of FIG. 2 over the embodiment illustrated in FIG. 1 is that the ballast circuit  21  of FIG. 2 is entirely self-contained in a relatively small volume without the need for a special dual capacitor arrangement of ballast  18  (e.g., capacitors  22  and  24 ) as shown in FIG. 1. Accordingly, the embodiment of the present invention depicted in FIG. 2 can be retrofit into an existing HID luminaire by modifying the wiring to the primary winding  26  of the ballast  23 .  
         [0030]    Further, it is important to note that the value of the resistor  32  is large enough to provide a sufficiently visible effect to any one in the vicinity of the luminaire, upon high and low cycling of the lamp  12  output via relay contact  16  during the warning period. However, the resistor value should be small enough to ensure heat dissipation is minimal. Accordingly, if the total period of cycling (e.g., cycling of power to indicate termination of lamp operation) is kept under a minute, and the duty cycle is kept to approximately 50%, then the heat dissipated by a 20 Watt or higher wire wound resistor is not large enough to result in component failure. Although the resistor  32  has to withstand high instantaneous power levels, the above described conditions (e.g., length of cycling time, and duty cycle&lt;50%) allow the components to function within acceptable limits.  
         [0031]    Turning now to the ballast circuit  31  of FIG. 3 which is illustrative of an additional embodiment of the present invention. This embodiment comprises similar components to FIGS. 1 and 2, for example, microcontroller  20 , power source  11 , the relay contact  14  and relay contact  16  controlled by microcontroller  20 , and lamp  12 . However, in FIG. 3, the ballast  33  comprises a core  30  with windings  26  and  28 , and resistor  32  in series with capacitor  22 . The relay contact  16  is in parallel with resistor  32 . Additionally, the resistor  32  is in series with the secondary winding of the ballast  33 , thus when relay contact  16  is open the impedance of the ballast circuit  21  is increased. This in turn reduces the power delivered to the lamp  12  and causes the lamp output to drop. Resistor  32  has a value of 30 ohms in this configuration, providing a sufficient reduction in lamp power and lumen output.  
         [0032]    Accordingly, in operation, microcontroller  20  operates relay contact  16  from a normally closed position to an open position, momentarily. Opening of relay contact  16  changes the impedance of the ballast circuit  31  thereby reducing current flowing to lamp  12 . This produces a visible dimming of the lamp  12  noticeable to anyone in the vicinity of the lamp  12 . The microcontroller repeats this process (e.g., opening and closing the relay contact  16 ) for a predetermined amount of time. After the expiration of this predetermined amount of time or warning period, the microcontroller  20  activates the normally closed relay contact  14 , thus disconnecting the power source  11  from the ballast  33  and extinguishing power to the lamp  12 , via a 120 Volt tap  19 . After a selected period of time, the microcontroller energizes contact  14  into a closed position and allows the lamp to begin to resume operation, until the next cycling period, for example, one week later. Although the ballast circuits of FIGS. 2 and 3 are similar, ballast circuit  31  of FIG. 3 is less likely to be retrofit due to the placement of the relay contact  16  and resistor  32  in series with the secondary winding  28 .  
         [0033]    The ballast circuit  40  of FIG. 4 is yet an additional embodiment of the present invention. The main difference between the ballast circuit  40  of FIG. 4 and that of FIG. 3, for example, is the use of a magnetically regulated ballast  34  in FIG. 4. The regulating ballast  34  comprises a 120 Volt tap  19  connected to the primary coil  36 , a secondary winding  38 , and a tertiary winding  37 . Further, the tertiary winding  37  has a capacitor  22  connected in parallel, along with a resistor  32  and a relay contact  16  coupled in parallel to the resistor  32 . The three windings are coupled together by a laminated core  42 .  
         [0034]    Accordingly, in operation when the time out period is attained, the microcontroller  20  activates the normally closed relay contact  16  into an open position. The current flows through a current limiting resistor  32  and reduces the current to the tertiary winding  37 . This, in turn, limits the current flow to the secondary winding  38 , and therefore causing lamp  12  to dim. The microcontroller  20  repeatedly activates and de-activates relay contact  16  for a predetermined period of time in order to give the effect of a dimming lumen output alternating with an increasing lumen output to anyone standing in the vicinity of the lamp  12 . As mentioned above, after expiration of the predetermined period of time, the microcontroller  20  operates the normally closed relay contact  14  in order to disconnect the power supply  11  from the ballast  34 , via a 120 Volt tap  19 . Upon expiration of an additional pre-determined period of time, the microcontroller releases the relay contact back into a closed position to enable the lamp  12  to resume operation, until the next cycling period, typically a week later.  
         [0035]    Although only several exemplary embodiments of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.