Electric lamp and discharge devices: systems – Plural series connected load devices – Christmas lights
Reexamination Certificate
2002-12-16
2004-10-19
Tran, Thuy Vinh (Department: 2821)
Electric lamp and discharge devices: systems
Plural series connected load devices
Christmas lights
C362S236000, C362S259000
Reexamination Certificate
active
06806656
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a twinkle light set, and more particularly to a fuse bulb twinkle light set which meets the safety objectives of the Underwriters Laboratory (UL) standards for safety.
UL Standard 588 distinguishes between the flasher bulb (LAMP, FLASHING) and the twinkle bulb (LAMP, INDIVIDUAL FLASHING) as follows:
5.16 LAMP, FLASHING—A series-or parallel-connected lamp that automatically cycles on and off by means of a bimetallic strip connected in series with the filament. For series-connected strings, the flashing lamp causes all lamps connected in series with it to flash. For parallel-connected strings, only the flashing lamp is intended to flash.
5.17 LAMP, INDIVIDUAL-FLASHING—A series-connected lamp that automatically cycles on and off by means of a bimetallic strip connected in parallel with the filament. The cycling of the bimetallic strip causes only the individual-flashing lamp to flash by momentarily placing a short across the filament to turn the lamp on and off.
It is well-known to provide a flasher light set wherein a flasher bulb (according to “5.16 LAMP, FLASHING”) contains a thermally sensitive element which opens and closes the electrical illumination circuit through the bulb according to its “hot” or “cold” state. When the circuit containing the thermally sensitive element opens, there is no electricity supplied to any other bulb in series electrical communication therewith, so that each such series-connected bulb is temporarily extinguished until the element cools and the circuit again closes. Thus, use of even a single flasher bulb causes an entire light set or a section thereof in series communication to have its bulbs flash on and off with the flasher bulb. The appearance of a light set in which all of the bulbs or a section of the bulbs flashes on and off in unison presents an aesthetic attraction to a viewer.
However, an even more appealing aesthetic effect is produced by a twinkle light set. Instead of a flasher bulb, the twinkle light set uses a twinkle bulb (according to “5.17 LAMP, INDIVIDUAL-FLASHING”). The twinkle bulb is similar to the flasher bulb in that a thermally sensitive element opens and closes the electrical illumination circuit which provides illumination of the bulb. However, whereas in the flasher light set no current passes through the bulb when the illumination circuit through the bulb is open, in the twinkle light set, each twinkle bulb has in parallel with the illumination filament a bypass or shorting circuit. The bypass circuit (when closed) presents a low resistance, whereas the illuminating circuit (when closed) presents a high resistance. As the twinkle bulb is illuminated through the illumination circuit, it heats up the normally open switch in the bypass circuit, thereby to close the switch and provide an alternative low resistance path through which the current will preferentially flow. This in turn terminates substantially all of the current passing through the high resistance illumination circuit and leads to cooling of the bulb. After a predetermined amount of cooling, the switch in the bypass circuit returns to its normally open state so that current must flow once again through the illumination circuit.
One major difference between a twinkle light set and a flasher light set is that each twinkle bulb acts independently of the other twinkle or standard bulbs in series therewith because the twinkle bulb always passes current therethrough (whether through the illumination circuit or through the bypass circuit). Thus, in a twinkle light set, a wide variety of aesthetic effects may be obtained dependent upon the placement of the twinkle bulbs. For example, a twinkle light set may consist of a plurality of substantially vertical light strings, with each bulb in a given light string being in series. A set of light strings (at least one light string being in each light string set) may contain only ordinary or standard steady burning bulbs, while an alternate set of light strings (at least one light string being in each light string set) may contain only twinkle bulbs. The standard bulbs remain on constantly, while the twinkle bulbs twinkle on and off independently of each other, seemingly at random, as a counterpoint to provide an enhanced aesthetic appearance. Clearly any given light string(s) may include both standard and twinkle bulbs for providing a more startling aesthetic experience.
In a conventional twinkle light set typically a large or major proportion of the bulbs (at least 50% thereof) are ordinary or standard steady burning bulbs. Thus, even if all of the illumination circuits of all of the twinkle bulbs were, through happenstance, to open at the same time, so that each of the twinkle bulbs presented only the low resistance bypass path to the current, the standard bulbs (with their high resistance illumination circuits) would dissipate the current sufficiently to ensure safety of the light set and prevent a dangerous burn-out.
However, it is known that some twinkle light set users prefer for aesthetic reasons to modify the purchased twinkle light set and convert it to an exclusively twinkle bulb light set by replacing each standard bulb of the light set with a twinkle bulb. As a result, when, by happenstance, all of the illumination circuits of all of the twinkle bulbs are open, the current passes substantially unchecked and undiminished through the low resistance bypass circuits in a decidedly unsafe manner which can lead to melting of conductors, burning of insulation, fires, and the like. While twinkle light sets are usually sold with instructions cautioning against the replacement of standard bulbs with twinkle bulbs, users do not always heed this caution.
Accordingly, recently enacted Underwriters Laboratory (UL) regulations, Section
588
, requires that a series-wired twinkle light set have a minimum of 35 (thirty five) bulbs per circuit (to minimize the current passing through any given bulb) and that at least eighteen of 35 (thirty five) bulbs be standard steady burning bulbs (as opposed to non-standard twinkle bulbs). This ensures that in each circuit of a series-wired twinkle light set there are an adequate number of ordinary bulbs to dissipate the current, even if by happenstance all of the twinkle bulbs are passing the current through the low resistance bypass circuits rather than the high resistance illumination circuits.
Commonly owned U.S. Pat. No. 6,474,841 describes a twinkle light set which meets the UL requirements by providing a plurality of standard bulb sockets which can operatively receive only a standard bulb (e.g., a conventional steady burning bulb or a flasher bulb) and a plurality of non-standard bulb sockets which can operatively receive a non-standard twinkle bulb or optionally a standard bulb. Thus, by limiting the number of non-standard bulb sockets, the manufacturer limits the number of twinkle bulbs which can be used in the light set.
Notwithstanding the safety of the twinkle light set according to the above patent, there are those who prefer relying on a fuse or fuse bulb such as that disclosed in U.S. Pat. No. 4,223,248. Fuse bulbs are well-known and, when properly used, clearly meet the safety objectives of the UL standards. However, this requires that the fuse bulb either be non-removable from the fuse bulb socket or, if removable, be replaceable only a like fuse bulb. Clearly the entire purpose of having a fuse bulb would be defeated if a blown fuse bulb could be replaced by a non-fuse bulb such as a steady burning bulb, a flasher bulb or a twinkle bulb since none of these alternative bulbs would protect against excessive current in the circuit.
Accordingly, it is an object of the present invention to provide a twinkle light set which in one preferred embodiment meets the safety objectives of the UL standards, and in particular Section
588
thereof, without regard to the relative numbers of standard and twinkle bulbs in an electrical circuit.
Another object is to provide such a twinkle light set which in one preferred embodimen
Amster Rothstein & Ebenstein
Sienna LLC
Tran Thuy Vinh
LandOfFree
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