A heat-sensitive variable-resistance insert device for use with a light bulb and socket including: a thin, heat-sensitive variable-resistance wafer and a perimetrical insulation member surrounding the edge of the wafer and electrically insulating it from the wall of the socket. The wafer has a contact area on one side for engaging the central contact of the socket and on the other side thereof for engaging the central contact of the light bulb, and an adhesive paste on that other side within the perimetrical member for adhering the device to the base of a light bulb.

FIELD OF INVENTION 
This invention relates to a heat-sensitive variable-resistance insert 
device for use with a light bulb and socket. 
BACKGROUND OF INVENTION 
When an electric light bulb is turned on, a sudden incoming surge of 
electrical current encounters the relatively low resistance (e.g. 3 ohms) 
typically exhibited by the cold bulb filament. The resistance of the 
filament may be only 1/41 that of its resistance at operating temperature 
(e.g. 125 ohms), and in such a case the initial current surge is forty-one 
times that of the operating current. Consequently, a weak or worn filament 
will often burn out at the moment the bulb is turned on. To remedy this 
problem and extend light bulb life, various lamp socket insert devices 
have been provided. These devices typically employ a variable-resistance 
thermistor, having contact means on either side thereof, which is 
interposed between the light socket and bulb contacts. When it is cold 
(e.g. when the electricity is turned off), the insert device exhibits a 
resistance which is typically higher than the normal operating resistance 
of the bulb filament. Accordingly, when the light bulb is turned on the 
initial current surge through the filament is reduced. As the insert 
device is heated by the current, its resistance drops so that an increased 
operating current is delivered to the filament. Simultaneously, the 
filament has typically attained an operating resistance which enables it 
to withstand the increased operating current. 
Several undesirable features are often exhibited by such insert devices. 
For example, insertion of the device into the socket is often awkward and 
typically requires the use of either fingers or tools, such as pliers. At 
times the installer may neglect to electrically disconnect the lamp, and 
therefore insertion presents a grave danger of electrical shock. 
Present light socket insert devices are often relatively thick. 
Consequently, they conduct heat relatively slowly and exhibit a smaller 
than desired drop between high and low temperatures. The initial 
protective resistance may be lower than desired, and thus premature 
filament burnout may still occur. Or, the operating resistance of the 
insert may be higher than desired, thereby unduly restricting current to 
the bulb filament. Power is thus wasted and the insert device is heated to 
such a high temperature that it may be suitable for use only in porcelain 
sockets, which are rated for high wattage bulbs, and not in ordinary 
metallic light bulb sockets. High operating temperature also poses the 
hazard of arcing. The mechanical stress and high operating temperatures 
often experienced by present light socket inserts may lead to cracking and 
reduced insert life. 
The relatively large thickness exhibited by certain of the present insert 
devices may also force the metal base of the light bulb to extend above 
the top edge of the light socket. Again, a hazard of shock is presented. 
Insulating washers and other devices have been provided for wrapping about 
the exposed base in order to reduce this danger. However, use of such 
insulating devices may be inconvenient and is often neglected. 
SUMMARY OF INVENTION 
It is therefore an object of this invention to provide an improved 
heat-sensitive variable-resistance insert device for use with a light bulb 
and socket which is relatively durable, inexpensive, and both easy and 
safe to install and utilize in a wide variety of light sockets. 
It is a further object of this invention to provide a heat-sensitive 
variable-resistance insert device which may be inserted without the use of 
fingers and/or tools, thereby simplifying insertion and reducing the 
hazard of electric shock. 
It is a further object of this invention to provide a heat-sensitive 
variable-resistance insert device which is permanently attached to a light 
bulb so that any attempt to remove it from the bulb results in destruction 
of the device and prevents its re-use. 
It is a further object of this invention to provide a heat-sensitive 
variable-resistance insert device which provides increased electrical 
resistance to initial current surges in order to prolong light bulb 
filament life and decreased operating resistance in order to conserve 
energy and operate at cooler temperatures. 
It is a further object of this invention to provide a heat-sensitive 
variable-resistance insert device which allows a light bulb to be fully 
inserted into a light socket, thereby reducing exposure of the base of the 
bulb above the socket and the hazard of shock created by such exposure, 
and eliminating the need for insulating devices for guarding against such 
shock. 
It is a further object of this invention to provide a heat-sensitive 
variable-resistance insert device which reduces arcing. 
This invention features a heat-sensitive variable-resistance insert device 
for use with a light bulb and socket, including a thin heat-sensitive 
variable-resistance wafer. A perimetrical insulation member surrounds the 
edge of the wafer and electrically insulates it from the wall of the 
socket. The wafer has a contact area on one side for engaging the central 
contact of the socket and on the other side thereof for engaging the 
central contact of the light bulb. An adhesive paste is provided on that 
other side of the wafer within the perimetrical member for adhering the 
device to the base of a light bulb. 
In a preferred embodiment, the adhesive paste may be a two-part 
catalytically activated adhesive with the two parts mounted adjacent each 
other on the wafer or may be a one-part heat-setting bonding paste. The 
paste may be viscid and temporarily adhere the wafer to the base of the 
bulb until the paste fully sets. The paste may be provided in an annular 
configuration on the wafer to enable the contact of the bulb to extend 
through the annular hole to contact the wafer. The insulation member may 
include a plurality of resilient elements on at least one of the surfaces 
thereof for cushioning the device against the base of a socket. The 
insulation member may be resilient and may be an elastomer material, or it 
may be a ceramic material. The wafer may be circular and the insulation 
member may be annularly disposed thereabout.

A heat-sensitive variable-resistance insert device for use with a light 
bulb and socket according to this invention may be effected using a thin 
heat-sensitive variable-resistance wafer. The wafer is typically composed 
of a thermistor ceramic which may include a mixture of manganese dioxide 
(MnO.sub.2) and nickel oxide (NiO). Preferred proportions include 85-90% 
manganese dioxide and 10-15% nickel oxide. 
A perimetrical resilient insulation member surrounds the edge of the wafer 
and electrically insulates it from the wall of the socket. The insulation 
member may be composed of a heat-resistant elastomer such as silicone 
rubber, or a ceramic or other material which is capable of withstanding 
the operating temperature of the bulb. The insulation member typically has 
a diameter which is smaller than that of the socket, thereby enabling 
interference-free insertion and removal of the insert device into and out 
of the light socket. Typically, the wafer is circular and the insulation 
member is disposed annularly thereabout. The wafer has a contact area on 
one side thereof for engaging the central contact of the socket and a 
contact area on the other side thereof for engaging the central contact of 
the light bulb. 
An adhesive paste is provided on that other side of the wafer within the 
annular insulation member for adhering the device to the base of a light 
bulb. This paste may include a two-part catalytically activated adhesive 
such as is used in auto body repairs and the like, and example of which is 
Duro DPI Auto Body Filler Putty, manufactured by Loctite Co. The two parts 
are mounted adjacent each other on the wafer. Such a paste may be viscid 
and temporarily adhere the wafer to the base of the bulb until the paste 
is mixed and fully set. Alternatively, the paste may be a single component 
heat-setting bonding paste. However, because such heat-setting bonding 
pastes often exhibit a limited shelf life (hardening after one or two 
years of non-use), the two-part adhesive is preferred. Such two-part 
pastes, which are often available in the form of two-layer ribbons, 
typically remain effective for an indefinite period because of a very thin 
skin which forms between the two layers and prevents mixing and thus 
setting thereof. In one embodiment, the paste may be applied to the wafer 
in an annular configuration so that the bulb contact extends through the 
annular hole to contact the wafer. Where the two-part adhesive is 
employed, such an annular paste may be divided into two semiannular 
halves, each comprising one of the two catalytically activated components. 
The two parts are mixed by the process of screwing the bulb into the 
socket. 
The advantage of the device of this invention lies in the fact that it is 
inserted into and removed from a light socket without tools or fingers, 
thereby reducing the hazard of electric shock. Because the paste is 
viscid, the wafer adheres to the base of the bulb and is inserted into and 
removed from the socket with the bulb. Further, because the adhesive 
utilized in this invention typically sets after a period of time (due to 
the mixing of the two-part catalytically activated adhesive or the heating 
of the single component paste), the device becomes permanently attached to 
the base of the light bulb. Thereafter, the thin heat-sensitive wafer 
tends to readily break if an attempt is made to remove it from the bulb. 
Thus the wafer cannot be removed from the bulb and replaced by itself in a 
light socket for re-use. 
The wafer provided in this invention is very thin: in standard light bulb 
and socket applications, a typical wafer is between 0.06 and 0.07 inch in 
thickness. Due to the thinness of the wafer, and thus its relatively low 
thermal mass, the device heats up very quickly. The cold resistance may 
range from approximately 100-200 ohms and the hot resistance may drop to 
approximately three ohms. The thin wafer also allows the light bulb to be 
fully inserted (screwed into) the socket. Exposure of the light bulb base 
above the socket is eliminated, thereby reducing the electrical shock 
hazard created by such exposure and the need for insulating devices such 
as washers for wrapping about the exposed base. 
A plurality of resilient elements may be provided on at least one of the 
surfaces of the annular insulation member to enable the member to adapt to 
the contours of different sockets and accommodate rivets, screws or other 
parts. Typically, such resilient elements include fingers formed by making 
a number of crossing radial and annular serrations on the surface faced 
away from the light bulb. 
There is shown in FIG. 1 a heat-sensitive, variable-resistance insert 
device 10 which is used with a light bulb 12 and a socket 14 according to 
this invention. Device 10 includes a thin heat-sensitive 
variable-resistance circular wafer 16 which exhibits a high resistance 
when cold and drops to a low resistance as it is heated. Wafer 16 includes 
a top surface contact area 15 and a bottom surface contact area 17. An 
annular silicone rubber insulation member 18 surrounds the edge of wafer 
16. Member 18 includes a channel 20 for receiving the circumferential edge 
of wafer 16 and has a diameter which is slightly smaller than that of 
socket 14. An adhesive paste 22 is mounted on the top surface 15 of wafer 
16 within insulation member 18. Paste 22 is a two-part catalytically 
activated adhesive which includes a first part 26 and a second part 28 
separated by a thin skin 30 which prevents mixing of parts 26 and 28, 
which would cause premature setting of paste 22. 
Bulb 12 includes a threaded periphery 32 and a base 34 which has a central 
bulb contact 36 at the bottom thereof. 
Socket 14 includes a threaded inside periphery 38 and a socket base 40. A 
springy socket contact 42 is mounted in a conventional manner to base 40 
and is urged upwardly in the direction of arrow 43. The heads of rivets 
44, 46 protrude from socket base 40. Insulation member 18 includes a 
plurality of resilient elements 48 in the bottom surface thereof. Elements 
48 enhance the resilience of member 18 and when device 10 is inserted into 
socket 14 and member 18 is urged against socket base 40, the elements 48 
provide a cushion against rivets 44 and 46. 
As shown in FIG. 2, bulb 12 is screwed into socket 14 with device 10 
attached to the base 34 thereof. Before inserting bulb 10 into socket 14, 
device 10 is applied to base 34 so that paste 22 comes in contact with 
base 34. Paste 22 is viscid and temporarily adheres wafer 16 to bulb base 
34. As bulb 12 is screwed into socket 14, paste 22 is pressed and twisted 
so that the two parts of the paste are mixed in a manner more fully 
described below to enable setting of paste 22. During such insertion, 
contact 36 is pressed through paste 22 until it comes in contact with the 
top contact surface 15 of wafer 16. Bulb 12 and the attached device 10 are 
screwed fully into socket 14 until the bottom surface contact area 17 of 
device 10 engages the springy central contact 42 of socket 14. Insulation 
member 18 bears against the tops of rivets 44 and 46 and because of the 
resilient elements shown in FIG. 1, the insulation member is cushioned 
against the rivets. 
When wafer 16 is cold, it exhibits a relatively high resistance (e.g. from 
approximately 100-200 ohms). When the light is turned on, incoming current 
passes from socket contact 42 through wafer 16 to bulb contact 36. The 
cold high resistance of wafer 16 reduces the initial current surge 
entering bulb 12. Insulation member 18 insulates wafer 16 from the inside 
wall 38 of socket 14 and prevents short-circuiting therebetween. 
Because of its thin dimension and low thermal mass, wafer 16 heats up 
relatively quickly and its resistance quickly drops to a low level (e.g. 
approximately three ohms). Full operating current is allowed to pass 
through filament 52, which by this point has attained its higher operating 
resistance. The low level of resistance exhibited by the heated wafer 16 
permits the full operating current to pass through the wafer, thereby 
reducing power dissipation and saving energy. Further, wafer 16 is heated 
to a lower temperature, thereby reducing arcing, prolonging the life of 
the insert device, and enabling the device to be utilized in all types of 
metal sockets. The thinness of wafer 16 also enables bulb 12 to be fully 
screwed into socket 14 so that the top of base 34 is not exposed about the 
top of socket 14. The hazard of shock is thereby reduced and the need for 
an insulation device for surrounding an exposed base is thus eliminated. 
There is shown in FIG. 3 a top view of device 10. Two-part paste 22 is 
applied to the top coated surface 15 of wafer 16. Skin 30 separates first 
part 26 and second part 28 and prevents mixing and setting of the parts 
prior to application of the device 10 to a bulb and insertion of the bulb 
and device into a light socket. 
During insertion of the bulb and device into the light socket, paste 22 is 
pressed and twisted so that the parts 26 and 28 are mixed in the manner 
shown in the sequence of FIGS. 4A-4C. The interface, originally a 
diameter, is twisted into a pinwheel configuration. Following mixture, the 
two-part adhesive paste sets, thereby permanently bonding device 10 to the 
base 34 of bulb 12, as shown in FIG. 2. 
An alternative manner of applying the two-component paste 22a to top 
surface 15a of wafer 16a is shown in FIG. 5. Therein, paste 22a is applied 
in an annular configuration comprising first and second parts 26a and 28a. 
Each part forms one half of the annular configuration, and a skin 30a once 
again separates the two bonding parts and prevents mixing thereof. Device 
10a is attached to the base of a light bulb in the same manner as device 
10 of FIGS. 1-4. In this embodiment, however, the bulb contact extends 
through the central hole 56a of the annular paste configuration, and thus 
directly engages the top contact surface 15a of wafer 16a without pressing 
through paste 22a. When the bulb and device 10a are inserted into the 
socket, the two parts 26a and 28a are mixed, similarly to the paste 22 of 
FIGS. 1-4. 
As shown in FIG. 6, a single component paste 22b may be applied to the top 
surface of a variable-resistance wafer. Paste 22b includes a heat-setting 
bonding paste. Device 10b is applied to the base of a light bulb so that 
paste 22b engages the base and temporarily adheres device 10b to the light 
bulb. The light bulb and attached device 10b are then inserted into a 
light socket. The device 10b operates similarly to the previously 
described devices 10, 10a of this invention. As wafer 16b heats up the 
paste 22b sets, thereby permanently bonding device 10b to the base of the 
light bulb. 
In either of the embodiments described herein, the wafer is made 
sufficiently thin so that once the device has become permanently bonded to 
the base of the bulb any attempt to remove the device from the base will 
result in breaking of the wafer, thereby making re-use of the insertion 
device independently of the bulb impossible. 
Other embodiments will occur to those skilled in the art: