Halogen lamp with high temperature sensing device

A lighting device including a temperature sensing device for controlling the operation of the light emitting device. The lighting device includes a housing, a reflector coupled to the housing, a bulb received in the housing, the bulb being connected to a source of electrical power, and a capillary tube thermostat received in the housing. The capillary tube is an elongated metal member having a hollow center filled with a vacuum charged fluid. The fluid is calibrated to open the thermostat between 150.degree. F. and 350.degree. F. The capillary tube thermostat is in electrical communication with the power source and is supported by the housing in thermal communication with the bulb. The thermostat extends along at least a portion of the length of the bulb. The thermostat is also in thermal communication with the reflector, and thus will open the thermostat contacts if an overheat condition is detected at either the bulb or the reflector.

FIELD OF THE INVENTION 
The present invention relates generally to a lighting device. More 
particularly, the invention relates to a lighting device having a 
temperature sensor for controlling the operation of the device. 
BACKGROUND OF THE INVENTION 
Light emitting sources used in conventional lighting devices may reach high 
levels of heat intensity. In some circumstances, the heat intensity may be 
high enough to ignite flammable materials that come into contact with the 
light emitting source. One such light emitting source is the halogen 
torchiere bulb. 
Typically the halogen torchiere lamp 10 includes a supporting member 12, a 
housing 14, a bulb 16 and a reflector 18. As illustrated in FIG. 1, the 
housing 14 includes an upwardly extending U-shaped surface supported by 
the supporting member 12. The housing 14 supports the bulb 16. Generally, 
the bulb 16 extends horizontally along the housing 14, and normally has 
electrical contacts at opposing ends. Each end of the bulb 16 supporting 
the electrical contacts is received in a socket 24, the socket 24 
supporting mating terminal contacts for electrically coupling the bulb 16 
to a power source 36, typically, via an on-off switch 38. The socket 24 is 
coupled to the housing 14 using known techniques such as spot welding or 
mechanical fasteners. 
The housing 14 also supports the reflector 18. In some prior art devices, 
the housing 14 and the reflector 18 are fabricated as a single unit. If 
the housing 14 and reflector 18 are separate components, the reflector 18 
is positioned in the housing 14 so as to direct the light from the bulb 16 
out of the housing 14. Typically a portion of the reflector 18 extends 
beneath the bulb 16, as illustrated in FIG. 1. Additionally, the housing 
14 supports a barrier member or guard 42 that prevents objects from 
falling into the housing 14 and contacting the bulb 16, shield 40 or 
reflector 18, and the bulb 16 is covered by a protective shield 40 to 
prevent inadvertent contact with the bulb 16. 
As reported in one news article, halogen bulbs tend to burn much hotter 
than incandescent and fluorescent bulbs. Halogen bulbs have been known to 
reach temperatures in excess of approximately 700.degree. F. Consequently, 
if the halogen bulb comes into contact with cloth, paper or other 
combustibles, these materials may be ignited. 
Many modern designs for the halogen lamp incorporate devices for regulating 
the operation of the halogen bulb. U.S. Pat. No. 5,733,038 describes one 
such regulating device. The device includes a sensor mounted on the 
reflector for generating a sensor light signal corresponding to the light 
intensity detected by the sensor. The sensor is electrically connected to 
a control circuit, which interconnects the lamp and a power source. The 
control circuit is capable of disconnecting the lamp from the power source 
upon detection that the sensor light signal has reached a level indicative 
of a condition that the reflector is covered by an object. The disclosed 
regulator does not measure temperature increases that may occur in the 
bulb due to malfunction or partial covering. 
U.S. Pat. No. 5,801,490 (hereinafter the '490 patent) describes another 
regulating device. The device disclosed includes a temperature sensor 
installed on the reflector, near the midpoint of the bulb. The temperature 
sensor comprises a thermostat electrically coupled to the lamp's 
electrical circuitry and a half-cylindrical mask. The mask prevents direct 
illumination of the thermostat body by the bulb, and the thermostat 
de-energizes the bulb when the sensed ambient temperature reaches a 
predetermined temperature. 
Under certain circumstances, hot spots may develop in the lamp at locations 
distant from the midpoint of the bulb. This occurrence has been the cause 
of great concern with respect to potential fire hazards associated with 
halogen lamps. As a result, the Underwriter's Laboratories, Inc. (UL), a 
widely recognized, independent, not-for-profit, testing organization, has 
implemented a safety standard designed to test for hot spots as various 
points relative to the axis of the bulb. 
The "lamp containment barrier" test, Standard 112, becomes effective Jun. 
1, 1999. In this test, the lamp is placed in a draft-free room and 
connected to a variable 120-volt power supply, and adjusted to produce the 
rated lamp wattage. The lamp is left in the "on" condition for 15 minutes. 
Without being compressed, a specially prepared cheesecloth pad is placed 
on top of the lamp so that the cheesecloth is centered along the axis of 
the bulb. The cheesecloth pad is positioned on the lamp such that the 
cheesecloth follows the contour of the guard. As a result, the cheesecloth 
extends over the edges of the guard at both ends, and is as close to the 
bulb as the lamp's construction permits. The lamp is to be operated until 
(a) the cheesecloth ignites (flames); (b) a hole develops in any layer of 
the cheesecloth; or (c) seven hours has elapsed. To successfully pass the 
test, there shall be no (a) ignition (flaming) of the cheesecloth; or (b) 
holes developed in any layer of the cheesecloth fabric due to elevated 
temperatures. 
For lamps including an automatic temperature regulating or limiting 
control, the test is repeated with the cheesecloth positioned at 90 
degrees with respect to the axis of the bulb and in any other position 
that results in a longer time for the control to operate. The test is then 
repeated with the cheesecloth in the position that resulted in the longest 
time for the control to operate, with the unit's wattage reduced in 50 
watt increments for dimmers that are continuous by changing the input 
voltage, or selecting a lower step wattage setting for dimmers that are 
not continuous, until the unit operates for seven hours without operation 
of the control device. 
To satisfy some barrier containment tests, a high temperature limiting 
sensor capable of detecting localized hot spots that may develop at remote 
locations along the bulb or within the reflector is needed. There is also 
a need for a simplified sensor that permits sensing a temperature and 
de-energizing the lamp without the use of electric sensing components. 
SUMMARY OF THE INVENTION 
The present invention is directed to a lighting device including a 
temperature sensing device for controlling the operation of the light 
emitting device. The lighting device includes a housing, a reflector 
coupled to the housing, a bulb received in the housing, the bulb being 
connected to a source of electrical power, and a capillary tube thermostat 
received in the housing. The lighting device also includes a shield that 
covers the bulb, and a guard that extends across the bulb to prevent 
flammable materials from contacting the reflector, shield or the bulb. 
The capillary tube thermostat is in electrical communication with the power 
source and disrupts power to the lamp if a predetermined temperature is 
reached. The capillary tube thermostat is an elongated metal tube placed 
in thermal communication with the bulb, such that the thermostat extends 
along at least a portion of the length of the bulb. The thermostat is also 
in thermal communication with the reflector, and thus will open the 
thermostat contacts if an excessive temperature is detected in the 
housing, particularly in the vicinity of either the bulb or the reflector. 
The center of the capillary tube is filled with a vacuum charged fluid. The 
fluid is calibrated to open the thermostat between 150.degree. F. and 
350.degree. F. The tube is vacuum sealed to prevent ambient temperatures 
and pressures from interfering with the operation of the capillary tube 
thermostat. 
The thermostat used may be manually resettable, whereby the lighting device 
must be disconnected from the power source and reconnected, or the 
thermostat may be manually reset by depressing a reset button to 
reestablish a connection to the electrical power source by manually 
closing the open contacts. However, power is restored to the bulb only if 
the temperature in the housing has dropped below a preselected 
temperature. Alternatively, the thermostat used may be an automatic reset 
type, whereby power is automatically restored to the bulb once the 
temperature in the housing drops below a predetermined value.

DETAILED DESCRIPTION 
The lighting device is a halogen lamp 10. The embodiment of the halogen 
lamp 10 shown in FIGS. 1-8 includes common elements. It will be understood 
that common reference numerals are used to describe common features of the 
embodiment of the halogen lamp shown in FIGS. 1-8. As shown in FIGS. 2-7, 
the lamp 10 formed in accordance with the teaching of this invention 
includes a supporting member 12, a housing 14, a bulb 16, a reflector 18, 
and a capillary tube thermostat 20. As described above, these elements are 
assembled using known techniques to form the lamp 10. 
The supporting member 12 supports the housing 14 directly as shown in FIGS. 
1-5 or indirectly as shown in FIG. 6, wherein a suspension member 34 
couples the housing 14 to the supporting member 12. The supporting member 
12 may be a rod, a wall, floor, ceiling or other structural member. 
As illustrated in FIGS. 1-7, the housing 14 may be coupled to the 
supporting member 12 in various orientations, e.g., the housing 14 
extending upwards, downwards or sideways. Additionally, the housing 14 
includes openings 22, which provide an additional pathway for heat 
built-up inside the housing 14 to escape. As the primary path for heat 
dissipation is through the open portion of the housing 14, the openings 22 
may be omitted. 
The capillary tube thermostat 20 is received in the housing 14, and 
includes a capillary tube 26 filled with a fluid under pressure, a switch 
housing 28, switch contacts 30 and a diaphragm (not shown). The capillary 
tube 26 is a thin elongated metal tube having a high coefficient of heat 
transfer. It will be appreciated that nonmetal materials having heat 
conductive properties similar to metals may be used to construct the 
capillary tube 26. 
The capillary tube 26 is placed in the vicinity of the bulb 16 in a manner 
that permits detection of a temperature increase in the housing 14, with 
particular emphasis on sensing temperature increases near the bulb 16 and 
the reflector 18. Generally, conductive and radiant heating of the 
capillary tube 26 are insignificant and pose little concern due to the 
tube's 26 small diameter. 
As shown in FIG. 7, the capillary tube 26 is placed in a circular 
configuration above bottom surface of the reflector 18 and the adjacent 
bulb 16. The capillary tube 26 is positioned so as to encircle the bulb 
16. This arrangement approximates two-dimensional temperature sensing. 
Here, temperature rises within the housing 14, particularly in the 
vicinity of the bulb 16 and the reflector 18, are sensed from at least two 
locations for each point along the axis of the bulb 16 located within the 
loop formed by the capillary tube thermostat 20. FIGS. 1-6 show another 
configuration of the capillary tube thermostat 20, wherein the capillary 
tube 26 extends linearly along at least a portion of the length of the 
bulb 16. 
The switch housing 28 retains the diaphragm (not shown) and supports the 
switch contacts 30 at the housing's 28 outer surface. The diaphragm is 
retained in the switch housing 28 in a manner that permits the diaphragm 
to cause the activation of the switch contacts 30 and the disruption of 
power to the lamp 10 (discussed below). 
The switch contacts 30 are electrically coupled to the electrical circuitry 
supplying power to the bulb 16 using known techniques. An electrical 
wiring housing 32 supported by the housing 14 retains the electrical 
connections for both the lamp 10 and the capillary tube thermostat 20. 
OPERATION 
As illustrated in FIG. 8, the capillary tube thermostat 20 is connected in 
electrical series with the bulb 16 and the on/off switch 38. The capillary 
tube thermostat 20 contains no live electrical sensing parts for detecting 
a rise in temperature. Instead, the capillary tube thermostat 20 is a 
hollow elongated metal member, wherein the hollow center is filled with a 
fluid under pressure. 
In the preferred embodiment, the capillary tube thermostat 20 is vacuum 
charged with selected fluids to give specific calibrations. When the fluid 
inside the capillary tube 26 reaches a preselected temperature, the 
calibrated setting, an increase in the fluid's vapor pressure results. 
This increase in vapor pressure induces a force on the diaphragm, causing 
the diaphragm to snap. This causes the switch contacts 30 to open, 
creating an open circuit between the lamp 10 and the electrical power 
source 36. The power to the lamp 10 will remain disrupted until the 
temperature of the fluid in the capillary tube thermostat drops below a 
preselected level. 
The capillary tube thermostat 20 used in this invention may be a 
conventional linear capillary tube thermostat. Examples of capillary tube 
thermostats that may be used are Model Nos. 10H11 (automatic reset) and 
10H14 (manual reset) available from Therm-O-Disc, Incorporated, 1320 South 
Main Street, Mansfield, Ohio 44907-0538. The automatic reset thermostat 
permits current to be restored to the lamp 10 once the temperature in the 
vicinity of the thermostat 20 drops below a preselected temperature, and 
the manual reset device continues to disrupt current flow to the lamp 10 
until the temperature in the vicinity of the thermostat 20 drops below a 
certain preselected temperature and the user manually resets the 
electrical circuit to the lamp 10 by either pressing a reset button or 
unplugging the lamp and reconnecting the lamp 10 to the source of 
electrical power. 
The thermal characteristics of the capillary tube thermostat 20 are 
dependent upon various criteria and, thus, may vary given the desired 
operating constraints to be imposed on the lighting device. For example, 
the 10H11 and 10H14 models can be set to open at a temperature rise 
between 150.degree. F. and 350.degree. F..+-.15.degree. F. The Model No. 
10H11, the automatic reset version, permits resetting of the contacts at 
approximately 40.degree. F. below the opening temperature. The 10H14, the 
manual reset thermostat, may automatically reset when exposed to 
temperatures below -31.degree. F. It will be appreciated that other 
capillary tube thermostats having opening temperatures in excess of 
350.degree. F. may be used, particularly since halogen bulbs may operate 
at temperatures in excess of 500.degree. F. 
There are a variety of configurations that may be employed to fabricate the 
lighting device 10. Thus, the disclosed embodiments are given to 
illustrate the invention. However, the disclosed embodiments are not 
intended to limit scope and spirit of the invention. Therefore, the 
invention should be limited only by the appended claims.