LONG LIFE TRAFFIC CONTROL LAMP AND SOCKET INSERT

Technical Field

The present invention relates generally to traf¬ fic control lamps, and more particularly, to a long-life incandescent traffic control lamp and a socket insert for use with a conventional traffic control lamp that will func¬ tion with solid state electronic traffic controllers having conflict monitors.

Background Art

Whenever a traf f ic control lamp used in stop lights and other traffic control devices burns out or other-* wi se needs replacement , a maintenance crew must be dis¬ patched to replace the lamp. The cost involved in changing such a lamp far exceeds the value of the lamp itself , often requiring lifting equipment to lif t personnel to the traf¬ fic s ignal which may be far above the street level , and the services of several persons to operate the lift, change the lamp , and direct traff ic . During the time period when the traffic control lamp is inoperative, traffic congestion and confusion of drivers and pedestrians may occur and an acci¬ dent may result. Until the maintenance crew arrives and the traffic control lamp is replaced , the services of traf¬ fic police are many times required, placing a burden on the police department. If the life of the traffic control lamp can be extended and fewer replacements required , substan¬ tial .savings will be realized and traffic flow will not be interrupted so frequently due to inoperative lamps.

I t i s we l l known that the use of a d i ode i n series with the f ilament of an incandescent lamp operated on alternating current significantly increases the li fe of the lamp , only requiring an increase in the lamp ' s wattage

rating to produce a lumen output equivalent to the lamp previously used. The diode provides half-wave rectified direct current to the lamp filament.

One approach to using a diode with a lamp is to install the diode in a disc-shaped support which is posi- tionable within the lamp socket with one contact surface in electrical contact with the center contact of the socket and another contact surface in electrical contact with the center contact of the lamp. The diode is positioned within the diode disc and is connected between the two contact surfaces. To facilitate proper alignment of the diode disc contact surfaces with the lamp and socket center contacts, the disc is sometimes provided with an adhesive which may be used to glue the disc to the base of the lamp and allows the disc to travel with the lamp as it is screwed into the socket.

Another approach is illustrated in U.S.. Patent No. 3,869,631, in which a diode is mounted within the lamp between the lamp base and the stem press of the lamp, exter- nal of the gas-filled glass envelope containing the lamp filament.

The use of such a diode disc or lamp will extend the life of a traffic control lamp? however, it has been found that the addition of the diode causes solid state electronic traffic controllers having conflict monitors to malfunction and indicate an error condition. When an error condition is indicated, the traffic controller for a stop light enters a conflict mode and automatically switches a red or yellow flashing signal to the entire intersection. it will therefore be appreciated that there has been a need for a long-life incandescent traffic control lamp and for a socket insert which may be used with conven¬ tional traffic control lamps to provide long life, but which are operable with solid state electronic traffic con- trollers having conflict monitors. The traffic control lamp and socket insert should provide for extended lamp

life with minimal energy loss, should be inexpensive t manufacture, and should use readily available component without unduly high power rating requirements. The presen invention fulfills this need and further provides othe related advantages.

Disclosure of the Invention

The present invention resides in a long-life in candescent lamp and a socket insert for use with convention- al lamps to provide long life. The lamp includes a sealed glass envelope, a first electrical contact external of the glass envelope, a second electrical contact external of the glass envelope and electrically insulated from the first contact, an illuminable filament disposed within the glass envelope and electrically connected between the first and second contacts, a rectifier means for rectifying current to the filament, and a resistive means for providing a re¬ sistive bridge between the first and second contacts. The resistive means has a resistance substantially in excess of the resistance of the filament.

More specifically, one of the first or second contacts is a base fixedly attached to the glass envelope and sized to be received in a socket, while the other of the first or second contacts is a center contact fixedly attached to the base and electrically insulated therefrom. A pair of lead wires extend within the glass envelope and the filament is electrically connected between the lead wires. The rectifier means is a diode electrically connec¬ ted between one of the pair of lead wires and one of the base or center contacts in series with the filament, with the other one of the pair of lead wires being electrically connected to the other one of the base or center contacts. The resistive means is a resistor.

In one embodiment of the invention, the resistor is electrically connected between the center contact and the base in parallel with the in-series combination of the

filament and the diode. In another embodiment of the inven¬ tion, the resistor is electrically connected between the anode and the cathode of the diode in parellel with the diode. When used with presently available solid state elee- tronic traffic controllers, the resistor has a resistance of no greater than 27K ohms. The diode rectifies the alter¬ nating current to provide a direct drive current to the filament to improve lamp life, and the resistor provides a low-current electrical bypass of the diode to avoid indica- tion of an error condition by the conflict monitor.

An alternative embodiment of the invention is a socket insert for use with a conventional incandescent lamp having a center base contact and operating on alternating current in order to extend the life of the lamp. The in- sert includes a support body positionable within a lamp socket between the incandescent lamp and the center contact of the socket. The support body has a first contact for electrical contact with the center contact of the lamp and a second contact for electrical contact with the center contact of the socket. A diode is electrically connected between the first and second contacts, and a resistive ele¬ ment is also electrically connected between the first and second contacts in parallel with the diode.

Other features and advantages of the invention will become apparent from the following detailed descrip¬ tion, taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a schematic drawing of an incandes- cent lamp embodying the present invention.

Figure 2 is a schematic drawing of an alternative embodiment of the lamp shown in Figure 1.

Figure 3 is a schematic drawing of a socket in¬ sert embodying the present invention for use with a conven- tional incandescent lamp, showing the insert position be-

tween the base of a lamp and a lamp socket prior to place ment of the insert within the socket.

Best Mode for Carrying Out the Invention As shown in the drawings for purposes of illustra tion, the present invention is embodied in an incandescen lamp, indicated generally by reference numeral 10. Th lamp 10 includes a sealed glass envelope 12, a metallic screw base 14 fixedly attached to the lower end of th glass envelope, a pair of lead wires 16 and 18, and an illuminable filament 20 disposed within the glass envelope and connected between the lead wires. Except as will be described hereinafter, the lamp is of conventional and well known design, and will not be described or shown in detail herein. One such incandescent lamp is shown and described in U.S. Patent No. 3,869,631, incorporated herein by reference.

In conventional manner, the lead wire 18 is con¬ nected directly to the base 14. The other lead wire 16 is connected to the cathode of a diode 22, and the anode of the diode is connected to ^' a center contact 24 of the base 14. The center contact 24 is fixedly attached to the base 14 and electrically insulated therefrom.

When the lamp 10 is screwed into a socket (not shown), the center contact of the socket engages and makes electrical contact with the center contact 24 of the lamp 10, and the base 14 engages and makes electrical contact with the correspondingly threaded portion of the socket. With alternating current provided to the lamp 10 through the socket, the diode 22 rectifies the current to the fila¬ ment 20 to produce a half-wave rectified direct current and provide the long-life characteristic of the lamp.

In accordance with the present invention, the lamp 10 also includes a bypass resistor 26 electrically connecting the center contact 24 with the lamp base 14. In the embodiment of the invention shown in Figure 1, the by-

pass resistor 26 is electrically connected between the anode and the cathode of the diode 22 in parallel with the diode. In the alternative embodiment of the invention shown in Figure 2, the bypass resistor 26 is connected in parallel with the in-series combination of the filament 20 and the diode 22. The bypass resistor 26 and the diode 22 are positioned within the lamp 10, external of the sealed glass envelope 12 containing the heated filament 20.

In both embodiments, the bypass resistor 26 has a resistance substantially in excess of the resistance of the filament 20 and provides a low-current bypass of the diode 22. In such fashion, the conflict monitor sensing circuits of the traffic controller with which the lamp 10 is used will sense a current path through the lamp 10 at all times. The bypass resistor 26 provides a continuous electrical path to the conflict monitor which is necessary to avoid the monitor indicating a specious error condition and entering a conflict mode. The current flow through the bypass resistor 26 when the diode 22 is back-biased will be at a substantially lower level than the current through the diode and filament when the diode is forward-biased with a drive current supplied to the filament.

It has been found that with many of the solid state electronic traffic controllers, a lamp 10 with a fixed resistance for the bypass resistor 26 of approximate¬ ly 22K to 27K ohms or less will operate satisfactorily and avoid malfunctioning of the traffic controller. The bypass resistor 26 should be selected with as high a resistance value as will operate satisfactorily with the traffic con- troller with which the lamp 10 is used to avoid any unneces¬ sary dissipation of energy during the portion of the alter¬ nating current cycle when the diode 22 is reverse-biased.

In the embodiment shown in Figure 1, the diode 22, and in the embodiment shown in Figure 2, the in-series combination of the diode 22 and the filament 20, have rela¬ tively low resistance and effectively short-circuit the

bypass resistor 26 when the diode is forward-biased t supply a drive current to the filament.

It is noted that while the lamp 10 has been des cribed as a traffic control lamp, the lamp of the presen invention may be used in other situations, such as security light monitored by a sensing circuit which wil not function when a diode is used in the conventional man ner to achieve long life for the lamp. It is also noted that the orientation of the diode 22 may be reversed or th diode may be connected between the lead wire 18 and the base 14, while still achieving the benefit of the present invention. Although an arrangement is shown and described using a single diode 22 for half-wave rectification, the present invention may be used when the alternating current powering the lamp is rectified to a greater or lesser _r ex¬ tent.

The bypass resistor 26 of the present invention may be a resistor of fixed value or may have the necessary resistance supplied by a variable resistor or other device having a resistive element, such as a thermistor. The by¬ pass resistor 26 and the diode 22 may be fabricated as dis¬ crete components, as an integrated circuit, or otherwise. Of course, the bypass resistor 26 can be produced by a com¬ bination of resistive elements in series or parallel produc- ing the desired resistance.

With the present invention, the bypass resistor 26 may be a discrete component of conventional design and will typically have a standard power rating which makes the component readily available and inexpensive. Using an al- ternating current with a line voltage of 110 volts and a resistance of 22K ohms for the bypass resistor 26, the maxi¬ mum power dissipated by the resistor is only slightly in excess of one-half watt.

While the lamp 10 of the present invention has been shown and described with the diode 22 and the bypass resistor 26 positioned within the lamp, the diode and by-

pass resistor may be located at any desirable location with¬ in or outside of the lamp, as dictated by manufacturing economics or design choice.

Another alternative embodiment of the invention is shown in Figure 3 and includes a socket insert, indica¬ ted generally by reference numeral 28. The insert 28 has a support body 30 with a disc shape sized for insertion into a lamp socket 32. The insert 28 is positioned within the socket 32 between a center contact 33 of the socket and a center contact 34 of a conventional lamp 36.

The insert 28 is provided with a first contact surface 38 positioned on one face of the disc body 30 for engagement and electrical contact with the center contact 34 of the lamp 36, and a second contact surface 40 position- ,ed on the opposite face of the disc body for engagement and electrical contact with the center contact 33 of the socket 32. Electrically connected in parallel between the first and second contact surface ^' s 38 and 40 is a diode 22' and a bypass resistor 26'. As described above for the first two embodiments of the invention, the bypass resistor 26* pro¬ vides a continuous electrical path through the lamp 36 even when the diode 22* is reverse-biased to prevent the traffic controller with which the conventional lamp 36 is being using from indicating an error condition and entering a conflict mode.

It will be appreciated, that although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the inven- tion. Accordingly, the invention is not limited except as by the appended claims.