Note: Descriptions are shown in the official language in which they were submitted.
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FIRE-SAFE HALOGEN TORCHIERE LAMP
BACKGROUND OF THE INVENTION
This invention relates to the field of halogen torchiere
lamps and, more particularly, to safety measures for halogen
torchiere lamps having horizontally installed bulbs.
A typical halogen torchiere lamp ha9 an upward-facing
lampshade mounted atop a long, upright stem. Most halogen
torchiere lamps for home use have a~double-ended, horizontally-
mounted halogen bulb set within the lampshade. Typically, as
shown in FIG. 1, a partly cross-sectional view o~ the head of a
traditional halogen torchiere lamp, a horizontal halogen bulb 4 is
mounted on two lampholders 3, which are installed on two tabs of a
U-shaped bracket 2. The bracket 2 i9, in turn, mounted on the
threaded screw brushing 7 of the stem about its central hole. Two
mounting tabs of U-shaped bracket 2 are used to install lampholder
3/reflector 26 assembly beneath bulb 4. The double-ended halogen
bulb 4 is installed in the lampholders 3 above reflector 26. A
half cylindrical glass shield 6 is held in position above the bulb
4 by means of two clips 17,18 to prevent contact by the user with
the bulb 4 and to guard against the scattering of particles of
bulb 4, should it shatter. Under reflector 26, there are lead
wires, terminal blocks or wire connectors (not shown).
Most halogen torchiere lamps for home use utilize a 300 watt
halogen bulb mounted within the lampshade. Naturally, the 300
watt halogen bulb generates intense heat, and generally has a
working temperature of 500~-600~C. The upwardly-directed heat is
further intensified by the upward reflection of the bulb's heat
and luminescence by the top surface of reflector 26 and by the
inside of lampshade 10. The half-cylindrical glass bulb shield 6,
while intended to protect the bulb 4, unfortunately impedes air
circulation and thereby contributes to the heat surrounding ~he
bulb 4. These factors all contribute to a serious problem during
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indoor use where halogen torchiere lamp9 are often placed near
draperies, curtains or other window treatments. These window
treatments or other materials such as clothing, paper or toy~, all
of which are often made from flammable material9, could cover the
upwardly-facing lampshade opening or could otherwise contact or
come close enough to shield 6, which i9 almost as hot as the bulb
4 itself and has a working temperature of 400-500OC, such that
such materials would then be caused to ignite from the intense
heat of the shield 6 and of its immediately surrounding area.
Unfortunately, there have been many instances in which this has in
fact occurred, causing severe burns, loss of life and extensive
property damage.
There have been many attempts to solve this problem by
guarding the shield 6 against contact with flammable materials.
Most of such attempts have concentrated on providing some sort of
protective covering for the torchiere lampshade, such as by
providing a transparent or wire mesh guard over the lampshade. In
one of such de~igns, for example, a convex wire a~sembly is
positioned on the opening of the shade (as shown in FIG. 2) to
form a grid 13. These prior art design9 intend to use the grid 13
to keep the ~lammable material a considerable di9tance ~rom the
hot glass shield 6. The purpose for such a arrangement is to mee~
a forthcoming Underwriters Laboratories' (UL) standard, according
to which two layers of cheese-cloth must not ignite after having
been draped over the lampshade opening for seven hours.
Although the prior art constructions mentioned above can pass
the UL safety test, there are still several shortcomings. One of
these shortcomings is that these designs often resulted in
unsightly shadows being cast on the ceiling abo~e the torchiere
lamp because of the light shining through the net or grid 13. A
second shortcoming is that, even if these shields were to be
configured in a convex fashion so as to be further away from the
bulb, the profile of the halogen torchiere lamp is thereby
degraded and made less appealing by an unsightly and protrusive
domed grid or convex wire net.
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The most important shortcoming of these de9igns from a safety
standpoint i3 the fact that a fire could still occur on a halogen
torchiere lamp that was tested and approved according to the UL
safety test if any material that accidentally covers the lamp is
thicker, denser or allows less air infiltration than the two
layers of cheese-cloth used in the UL safety test. This is due to
the fact that the heat produced by tlle halogen bulb cannot be
quickly dissipated by the lampshade surface lO and the cover 13,
and the temperature gradient from bulb 4 to cover 13, to shade lO,
and to reflector 26 will be gradual. In normal condition, the
temperature of the reflector will exceed 100~C. In covered
condition, however, the temperature~of the reflector exceeds
200~C. Therefore, the insulation of the wiring system (including
the lead wire, the terminal block, the wire connector and the
sleeving) in the area surrounding the reflector 26 and U-shaped
bracket 2 and touching same will be degraded such that a fire
caused by a short-circuit will take place. In addition, if the
material that covers the lamp is flammable, i.e., it ha~ a
temperature limit of 200~C, it will become charred and will then
ignite due to the intense heat above the bulb.
It is desirable, therefore, to avoid conflagrations caused by
contact or proximity of flammable material to a halogen torchiere
lamp shield, but without degrading either the appearance of the
lamp or the light cast by the lamp.
It is also desirable to guard a halogen torchiere lamp
against causing fires through contact with nearby material or
through being covered thereby by providing an additional safety
measure to prevent excessive temperatures in the vicinity of the
halogen bulb.
It is further desirable to provide an apparatus for turning
the halogen torchiere lamp o~f when the temperature inside the
lampshade reaches a point at which fires could be caused by the
high-temperature region about the bulb.
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SUMMARY OF T~E INVENTION
According to the invention, a flat grid formed by plurality
of parallel wires with a circular border is installed flush with
or slightly below the opening of the 9hade in order to prevent
flammable materials from contacting the glass shield. A
temperature sensor i9 installed within the lampshade on the
re~lector, near the midpoint of the bulb. ~hen the lampshade
opening is covered by any material, the upper portion of the
lamp~hade acts as a greenhouse, i.e., the ambient temperature of
the upper portion rises gradually. The temperature sensor located
in the path of hot air flow passes the temperature sensed to a
connected shut-off circuit. When t~e ambient temperature inside
the covered lampshade exceeds a partlcular preset threshold value,
the power circuit of the lamp i9 automatically triggered to shut
the lamp off before the high temperature causes a fire.
Another embodiment of the invention utilizes the dimmer
circuit that is already present in many halogen torchiere lamps.
A control circuit with a thermistor circuit is coupled to the
dimmer circuit within the prior art circuitry inside the halogen
lamp for automatically adjusting the output power. When the
ambient temperature sensed by the sen90r exceed9 the particular
preset threshold value, the power of the lamp will be reduced,
rather than shut off, so that the bulb shines le~s brightly and
thereby emit~ less heat. The ambient temperature within the lamp
is thereby maintained at a safe level, and the lamp continues to
provide light for the user. As described above, this invention
avoids fires being caused by the lamp~hade opening being
unintentionally covered by any kind of material.
Accordingly, it i9 one object of this invention is to provide
a safety construction for traditional halogen torchiere lamps to
prevent a fire that could occur when the lampshade is covered by
any material.
It is another object of this invention to avoid fires caused
by contact or proximity o~ fabrics to 9hield 6 of a halogen
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torchiere lamp without degrading either the appearance o~ the lamp
or t:hc light cast by ~he lan~p.
It is a further object of this invention to guard a halogen
torchiere lamp against causing fires through contact with or
through bein~ covered by nearby materials by providing an
additional safety measure to prevent excessive temperatures in the
vicinity of the halogen bulb.
It is yet another object of this invention to provide an
apparatus for turning the halogen torchiere lamp off or for
lowering the intensity of the lamp when the temperature about the
bulb of the lamp reaches a point at~.which fires could be caused by
the high-temperature region a~out the hul~.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects of the invention will be apparent
upon consideration of the following detailed description, taken in
conjunction with the accompanying drawings, in which the reference
characters refer to like parts throughout and in which:
FIG. 1 is a partial cross-sectional view of the head of a
traditional halogen torchiere lamp head;
FIG. 2 is a side elevational view of a traditional halogen
torchiere lampshade equipped with prior art lampshade guard;
FIG. 3 is a cross-sectional view of a halogen torchiere
lampshade equipped with the invention, showing the convective
current air flow when the lampshade opening is covered by any
material;
FIG. 3a is a cross-sectional view of a halogen torchiere
lampshade equipped with the invention, showing the temperature
gradient when the lampshade opening is covered by a wooden plate;
FIG. 4 is a top perspective view of a first embodiment of
this invention, showing the location of each component;
FIG. S is a top perspective view of the sensor u3ed in.FIG.
4, showing the thermostat and the mask;
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FIG. 6 is the circuit diagram of a first embodiment of this
invention;
FIG. 7 is the circuit diagram of a second em~odiment of this
invention;
FIG. 8 is the circuit diagram of a third embodiment of this
invention; and
FIG. 9 is a schematic diagram of the third embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2, a p~ior art halogen torchiere
lamp typically has a double-ended, horizontally-mounted bulb 4 set
within the lampshade 10. Horizontal halogen bulb 4 i9 supported
within lampshade 10 by two lampholders ~, having appropriate lead
wires (not shown) and is mounted on a U-shaped bracket 2. Bracket
2 i9 installed on the threaded screw brushing 7 of stem 11 about
it~ central hole. Instead of a traditional flat reflector 26, an
optional prior art reflector assembly (not shown), which has the
~hape of a wide, low-profile rectangular or trapezoidal raised
section for reflecting light from bulb 4 upward and out of
lampshade 10, may be mounted beneath bulb 4. The double-ended
halogen bul~ 4 is installed in the lampholders 3 above the
reflector assembly 26. A half cylindrical gla99 9hield 6 i9 held
in position above bulb 4 by means of two clips 17,18 that attach
to lampholders 3 in order to prevent contact by the user with bulb
12 and to guard against scattered particles of bulb 4, should it
shatter .
In addition, prior art halogen torchiere lamps often also
include a wire or mesh grid, referred to as guard 13, as shown in
FIG. 2, that forms a dome-like convex projection above lampshade
10. When a flammable fabric falls over lampshade 10, grid 13
provides a large air space l'buffer zone" above bulb 4 in order to
prevent fires from being caused by the flamma~le material being in
too close proximity to heated bulb 4. As discussed, the profile
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o~ the torchiere lamp is thereby degraded. However, a fire may be
caused even in the event that the air space provided by guard 13
i9 sufficient to enable the halogen torchiere lamp to pass the
above-discussed UL sa~ety te~t; thi5 may occur if the ~lammable
fabric that i5 unintentionally placed over lampshade 10 is
thicker, denser or allows less air filtration than the two layers
of cheese-cloth used in the UL safety test. This is due to the
fact that the ambient temperature within the limited air space
inside lamp9hade 10 between bulb 4 and grid 1~, which i9 being
continuously heated by bulb 4, may eventually rise to the
temperature at which the flammable material combusts.
An embodiment of the invention i9 shown in FIGS. 3 and 4. In
FIG. ~, the lamp~hade opening is shown covered by any material 8,
such as a window treatment, clothing or a flammable object such as
a toy, which rests on grid 13. ~ulb 4 heat9 its surrounding air
and produces the convection air current shown by the arrows 24. A
slot 22 is cut through reflector 26 on each side of bulb 4 in
order to assist in forming the convective current loop. The
shapes and the dimensions of slots 22 can be determined by
hydrokinetics. One slot is located between bulb 4 and sensor 25,
as shown in FIG. 4, and the other slot is located on the other
side of bulb 4, opposite sensor 25.
If no slot 22 is made in reflector 26, when the shade opening
is covered by a wooden plate 30, as shown in FIG. 3a, the air
convection inside the limited space formed by said plate,
reflector 26 and shade 10 will stop quickly. Once the air ;
convection stops, the temperature gradient chart will be as shown
in FIG. 3a. The wooden plate (just above bulb 9) has the highest
temperature (600~C), and reflector 26 at the location just below
bulb 4 also has a rather high temperature (at least 2500C).
Sensor 25 will reach temperature beyond its action point ~150~C)
and, as will be discussed below, will restrict the bulb output.
However, the components of the wiring system abovetbeneath
reflector 26/U-shaped bracket 2, which components have safety
temperature limit~ as follows: wire connector-150~C; sleeved
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power cord-150~C; lead wire-200~C; terminal block-150Oc; and nylon
binder-~C, may be touchin~ r~lector 26 or bracket 2, perhap~
causing their temperatures to rise beyond their respective ~afety
limits. Thu~, the insulation of the wiring 9y3tem will be
degraded and a fire caused by short-circuit will take place.
In general, the top of sensor 25 should be no higher than
bulb 4 in order to prevent a shadow from being cast by sensor 25
outside lampshade 10. Sensor 25 may consist of a thermostat 31 as
shown in FIG. 5. Sensor 25 may be fit into any halogen torchiere
lamp using the simplest control circuit, a9 shown in ~IGS 6 and
7. Sensor 25 may also consist of a thermistor 34, which has a
more complicated control circuit diagram, a9 9hown in FIG. 8. The
internal lampshade arrangement in each embodiment has the same
configuration as shown in FIG. 3 except for the electrical
function of sensor 25.
FIG. ~ shows lampshade ~uard 13 having a circular shape.
Uowever, any border shape of guard 13 can be used, such as
rectangular, square, elliptical, etc. Lampshade guard 13 should
be formed of wires that extend across the top of the lampshade in
such a way as not to cast shadows. Several parallel wires extend
across the lampshade in a direction that i9 not co-planar with,
but is preferably perpendicular to, that of halogen bulb 4 and in
a convex profile. Thus, because the wires are not co-planar with
the bulb, shadows are not cast.
In the first embodiment of this invention, sensor 25
comprises a thermostat 31, as shown in the controlling circuit
diagram of FIG. 6. Thermo3tat 31 is u9ed because automatically
resetting thermostats are common and are widely used in primary
circuits for automatically breaking/connecting the circuit based
on ambient temperature. If thermostat 31 is chosen with its
current rating, ~ay 1 A, 2 A, etc., thermostat 31 can replace the
original fuse used in the lamp. FIG. 5 show9 that the sensor 25
of this invention consists of two main parts, the first of which
is the automatically-resetting thermostat 31 and the second of
which is a half-cylindrical mask 30. It is preferred that mask 30
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extend slightly higher in height than thermostat 31 in order to
~revent direct illumination of the thermo~tat body 31 by bulb ~,
as this would cause thermostat 31 to read an artificially high
temperature. The air buffer space formed between mask ~0 and
thermostat 31 is intended to allow for air flow to prevent the
temperature sensed by thermostat 31 from being affected by the
proximity to mask 30, which is illuminated'directly by bulb 4.
Mask ~0 is preferably formed of an aluminum sheet, the
thickness of which has no limit but in normal use i9 preferably
0.4 mm to 0.7 mm. Mask 30 can be attached to thermostat 31 by
fir9t being clipped to the thermo5tat 31 and then being glued to
it by epoxy resin. Ma~k 30 can the~ be fixed on reflector 26 by
its extended portion, which has an eyelet 27 through which a rivet
i9 passed to form a mechanical attachment. Other means of
attachment can also he used. Insulating sleeve9 9hould be used on
the leads of thermostat 31 according to safety requirements. For
a halogen torchiere lamp with a 300 watt bulb and a lampshade
opening diameter of twelve inches, a 130~C rating thermostat 31 is
used .
Thus, when the lamp is turned ON and any material covers the
lampshade opening, thermo~tat 31 will disconnect the electrical
power to the bulb before the covering material reaches 250~C and
ignites. In this case, the temperature of the central wire grid
is set to reach approximate maximum temperatures of 150~C
uncovered and 250~C covered, respectively. In normal use, when
the halogen torchiere lamp is turned ON at its full output wattage
(generally 300 watts), i~ the shade opening is covered by any
material, thermostat 31 will automatically cut off power to bulb 4
within approximately twenty seconds, as the maximum allowed
temperature is quickly achieved. Then, after approximately twenty
minutes, the cooled halogen torchiere lamp will turn back ON.
Since the life expectancy of the thermostat is approximately
l0,000 ON/OFF cycles, the lifetime of this inventive device is
acceptable.
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FIG. 7 shows the circuit diagram of the 9econd embodiment of
this invention. In this case, the halogen torchiere lamp is
equipped with an electronic dimmer, and thermostat 31 can be put
in series with said dimmer so that the dimmer will automatically
adjust the output power. When the dimmer is adjusted to the full
ON position, the output of the halogen lamp is 300 watts. The
re~ulting ON/OFF cycle will he the same a9 .that di5cu99ed above
with respect to the first embodiment. When the dimmer i8 adjusted
to any position other than the full ON position, the lamp's output
will be less than 300 watts and the re9ult will be safer than that
mentioned in the first embodiment. In this lower power po9ition,
for example, 150 watts, thermostat 31 will not act to shut the
power off since the ambient temperature within lamp~hade 10 does
not exceed the action point of the thermostat 31. Thus, ~ecause
the ambient temperature within lampshade 10 does not get too high,
the flammable material will not combust.
However, over an extended period of time during which
lampshade 10 is covered, the ambient temperature within lampshade
10 sensed by thermostat 31 will rise and exceed the preset
threshold value. In this in~tance, the dimmer will automatically
lower the bulb output. Thus, the brightness of bulb 4 and the
heat emitted is reduced, while the am~ient temperature within
lampshade 10 is maintained at a safe level. During the time that
the ~ulb output is reduced, bulb 4 is allowed to cool somewhat
while still providing light to the user.
In the two embodiments described above, in order to pr~vent
thermostat 31 from having an endles~ ON/OFF cycle caused by the
covered lampshade opening, a resistor Rp packed by 0.2 mm thick
insulation taper and rated 2 K Ohm/5 Watt can be connected in
parallel to thermostat 31, as shown by the wiring with dotted
lines in both FIGS. 6 and 7. Resistor Rp is bound to thermostat
31 by suitable means. Therefore, once thermostat 31 is OFF,
electric current will pass through resistor Rp, and the heat
produced hy resistor Rp will keep thermostat 31 on its OFF
condition until the user unplugs the lamp. After the lamp is
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unplugged, there will be no current in resistor Rp, and the
temperature of resistor Rp as well as thermostat 31 will revert
thermostat 31 to the ON position. Thi9 add5 an additional safety
feature for preventing fires from taking place by requiring the
user to unplug and then re-plug the lamp in order for the lamp to
function further. Besides this function, the user i9 also
required to remove the covering of the lampshade opening before
turning ON the lamp, otherwise this cycle will repeat.
Alternatively, this additional safety feature can be
accomplished simply by using a thermo9tat having the property
that, once it is OFF, the lamp must be unplugged in order to reset
it. Thus, in this version, re9isto~r Rp can be omitted in favor of
this specific type of thermostat.
FIG. 8 shows the circuit diagram of the third embodiment of
this invention. In this case, sensor 25 consists of a thermistor
34, preferably SDT1000 rating. Additionally, a photocell,
preferably S740 rating, is installed in order to supply DC current
to thermistor 34 so that there is sufficient bias to control the
transistor, preferably MJE 13003, which in turn control~ the
triac, preferably Q4010L4. Installation of thermi9tor 34 onto
mask 30 is similar to installation of thermostat 31 onto mask 30,
a~ discussed above. Photocell 15 can be installed in a location
within the lampshade which is cooler, for example, at a location
farther from the bulb than the location of thermistor 34. As
shown in FIG. 8, capacitor Cl i9 preferably rated 4.7 1IF/16 V,
capacitor C2 is preferably rated 0.068 ~F/250 V, and rheost~t R1
is rated 1 K Ohm.
The difference between the third embodiment and the first and
second embodiments is the electronic circuit diagram and their
functions. In first and second embodiments, sensor 25 senses that
the ambient temperature within lampshade 10 exceeds a
predetermined value and either simply cuts off the power supply to
the lamp and thereby shuts the lamp OFF or utilizes the dimmer to
reduce the power output o~ bulb 4. But in the third embodiment
(see FIG. 8), thermistor 34 senses the ambient temperature within
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lampshade 10 and thus varies the bias on the gate of the transis-
tor. The resistance (R c-e) of 9aid transistor will continuously
be changed accordingly and, therefore, the charging current on the
left side of the trigger diode will be controlled accordingly.
This in turn controls the dimness degree of the triac.
Photocell 15 can be arranged so that, when bulb 4 i9 in its
half output condition, the output of photocell 15 can still make
the transistor work.
Thermistor 34 can be packed with several layer~ of sleeves in
order to increase the thermal capacity of the whole sensor 25.
That is, when the ambient temperature within the lampshade reaches
130~C, the thermal gradient of the sleeve layers must be at least
10~C. Then, thermistor 34 senses a temperature of 120~C and the
transistor functions to dim bulb 4 slightly. But, 9ince the
sleeve layers still pas~ some thermal energy to thermistor 34,
~ulb 4 will be dimmed further. Even if bulb 4 i3 completely
turned off, the sleeve layers will maintain the bulb's temperature
at no less than 120~C for at least ten minutes. This arrangement
prevents the length of the period of the ON/OFF cycle of the bulb
4 from being too short, such as less than ten minutes. This
arrangement can be used in all embodiments of this invention,
especially if a low-rating (say, 120~C or less) thermostat/ther-
mistor i9 used. In doing so, mask 30 can be replaced by an
enclosure of any suitable ~hape. This method is used e~pecially
when thermostat 31/thermistor 34 has a lower temperature rating,
such as 120~C, instead of the original 130~C rating.
In FIG. 8, switch SWl, switch SW2 and the potentiometer VR
(preferably 500K, l~ Watt) are coaxial. When the common axis is
turned clockwise, SWl is ON first, the potentiometer is then from
the low voltage to the high voltage, and SW2 is ON. Since
initially bulb 4 (preferably 300 watt and 230 volt) is dim, the
photocell does not have enough output to push the transistor.
Thus, the triac will not work and bulb 4 will remain dim.
Therefore, SW2 must be always in its ON position in order to make
the whole circuit a traditional one, since the two leads of the
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bridge B ~4 x lN4007) are short-circuited by SW2. When the common
axis is turned to the mid point, for example, the half output of
bulb 4, SW2 is arranged OFF since now the brightne9s of bulb 4 has
enough energy to push whole inventive circuit to work.
In practice, SW2 can be replaced by a separate switch such as
a push-button switch, rock switch or a dip switch, etc. SWl can
also be separate from the potentiometer. In FIG. 9, rock
switches SWl and SW2 together with the potentiometer VR are all
installed in the stem of the lamp. One button PN i9 used to
control all three. When button PN i9 pu9hed downward, knob El
pushes ON the SWl first. When button PN continues further down
and reaches its middle point, knob ~2 pu9he9 the SW2 OFF. If
button PN i9 now pushed upward, SW2 will be pushed ON first, after
which SWl will be pushed OFF. Such an arrangement is preferred
when a sliding potentiometer i9 used.
Thus, a fire-safe halogen torchiere lamp is provided. One
skilled in the art will appreciate that the present invention can
be practiced by other than the described embodiments, which are
provided for purposes of illustration and not limitation, and that
the present invention is limited only by the claims that follow.
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