Abstract:
An improved fluorescent bulb for use in a work lamp for rough service applications. The fluorescent bulb is of the type having a fluorescent tube which emits light when energized by electric power. A base portion connects to the fluorescent tube and encloses a base cavity which supports a starter switch bulb electrically connected to the fluorescent tube. The starter switch bulb is protectively surrounded by a preferably woven glass-fabric sleeve which absorbs impacts caused by relative movement of components within the base cavity, including the starter switch bulb itself.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention generally pertains to light bulbs and lamps. The invention relates more particularly to a fluorescent bulb having a prophylactic sleeve surrounding a starter switch bulb which produces an electric discharge arc for initiating delivery of electric power through a fluorescent tube. The prophylactic sleeve helps reinforce and prevent the fluorescent bulb from breaking or otherwise malfunctioning when used with a work lamp in rough service applications. 
     Work lamps and shop lights have been developed for rough and rugged use by automotive mechanics, plumbers, technicians, etc. to durably and reliably light work areas. They commonly utilize fluorescent bulbs which must be sufficiently protected from impacts and other harsh jarring conditions which may cause the bulb to break or otherwise malfunction. Fluorescent bulbs typically include a light-emitting glass-tube connected to a base portion supporting a starter circuit. And the starter circuit typically comprises a heat sensitive switch encased in a secondary glass starter bulb. 
     Because the starter circuit functions to initially energize ionizable gas contained in the glass-tube for producing visible light, it is particularly important to keep it sheltered from harm. It is known, however, that the starter circuit, and particularly the glass starter bulb, is vulnerable to breakage or other damage from impacts caused by the relative movement of components disposed within the base portion, including the starter bulb. For example, because the starter bulb is typically suspended in the base portion only by flimsy wire conduits, the starter bulb may move and strike the inner surface of the base portion when subject to an impact. This vulnerability is aggravated when subject to rough service conditions of a demanding work environment. 
     Various measures have been developed to make fluorescent bulbs more durable by protecting, and thereby ensuring the proper operation of, the starter switch bulb. For example, in U.S. Pat. No. 5,675,941, a fluorescent lamp is disclosed having a hole along a base portion, through which an electrically and mechanically insulating material 150 is injected. As can be seen in FIG. 4′, the insulating material contacts a top portion of the glow starter switch, a portion of the fluorescent tube which extends into the base, and optionally a capacitor. 
     The arrangement of the &#39;941 patent, however, may allow a substantial portion of the starter bulb to be left exposed and unprotected (see FIG. 4′). Especially where moveable components are similarly disposed within the base of the fluorescent bulb, impacting contact with the starter bulb may be possible. Furthermore, notwithstanding the flexible nature of the injected compound, the cantilevered support arrangement at the top end of the starter bulb, as shown in FIG. 4′, may produce localized stresses in the starter bulb when, for example, the work lamp (and the fluorescent bulb) falls and strikes the floor in a lateral manner. 
     In summary, therefore, there is a need to provide a means for absorbing impacts against the starter bulb arising from the relative movement of components within the base cavity of a fluorescent bulb. In particular, padded protection of the sides of a starter bulb to impart a cushioning effect would be particularly advantageous due to the lateral direction of most impacts. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved fluorescent bulb having a protective sleeve surrounding a starter switch bulb, wherein the protective sleeve is adapted to absorb impacts caused by relative movements of components held within a base portion of a fluorescent bulb, including the starter switch bulb. 
     The present invention is for an improved fluorescent bulb for use in a work lamp for rough service applications. The prior art fluorescent bulb is of a type having a fluorescent tube adapted to emit light when energized by electric power. The fluorescent tube is connected to a base portion having a base cavity, and a starter switch bulb is supported within the base cavity. The starter switch bulb is adapted to produce an electric arc for initiating delivery of electric power through the fluorescent tube. Additionally, the improved fluorescent bulb has a prophylactic sleeve surrounding the starter switch bulb, which is adapted to absorb impacts due to relative movements of components disposed within the base cavity, especially during rough service applications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is partly cross-sectional view of the base end of the fluorescent bulb. 
     FIG. 2 shows a perspective view of the prophylactic sleeve alone. 
     FIG. 3 is a partly cross-sectional view of the prophylactic sleeve surrounding the starter switch bulb only. 
     FIG. 4 shows a partly cross-sectional view of the prophylactic sleeve surrounding both the starter switch bulb and the capacitor together. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIG. 1 shows a prior art fluorescent bulb, generally indicated at reference character  10 . It is known to use such fluorescent bulbs  10  in portable work lamps and shop lights (not shown) commonly employed by automobile mechanics, plumbers, etc. for rough service applications. The prior art design has a fluorescent tube, generally indicated at reference character  11 , and preferably has a glass construction. Moreover, the fluorescent tube  11  preferably has a U-shaped configuration (not shown) with a first end  12  and a second end  13  secured to a base, generally indicated at reference character  14 . The tube  11  is of the type having an evacuated interior into which an ionizable gas is injected, such as mercury vapor. The inner surface of the tube  11  is typically coated with a phosphorous layer by which visible light is converted from ultra-violet rays produced by ionizing mercury vapor. 
     As shown in FIG. 1, the base  14  has an upper base portion  16  with an upper base sidewall  17  and an upper deck  18  extending transversely from the upper base sidewall  17 . The upper base portion  16  is preferably constructed of a rigid metallic material, such as aluminum, but is not limited only to such. The two tube ends  12 ,  13  extend into a pair of holes  19  located on the upper deck  18 , and are preferably rigidly affixed to the upper base portion  16  with an adhesive  27 . The upper base portion  16  is connected to a lower base portion  20  preferably constructed of a rigid polymeric material. The lower base portion  20  has a lower base sidewall  21 , a switch cavity sidewall  23 , and a lower deck  22  transversely connecting the lower base sidewall  21  with the switch cavity sidewall  23 . The switch cavity sidewall  23 , together with a lower endwall  23 ′, encloses a switch cavity  24  which houses a starter circuit (see discussion below). The upper base portion  16  and the lower base portion  20  together enclose a base cavity  15  which includes, and is continuous with, the starter switch cavity  24 . As shown in FIG. 1, the tube ends  12 , 13  extend partially into the base cavity  15 . Along the lower deck  22  of the lower base portion  20 , a pair of electrical metal contacts  25  and  26  are externally mounted for connection to electrodes of an electric power source (not shown). As shown in FIG. 1, the first contact  25  connects to the left tube end  12  by means of an electrical wire conduit  28 . Likewise, the second contact  26  is electrically connected to the right tube end  13  by means of an electrical wire conduit  29 . More particularly, the electrical wire conduits  28  and  29  extend into the evacuated interior of the respective left  12  and right  13  tube ends and connect to filaments (not shown) which are heated during ignition of the fluorescent tube  11 . 
     A starter circuit is shown in FIGS. 1,  3 , and  4  positioned within the switch cavity  24  formed by the switch cavity sidewall  23  and the lower endwall  23 ′. The starter switch circuit comprises a starter switch bulb  29 , preferably having a glass shell  30  and heat-sensitive contacts  31 . The starter switch bulb  29  is electrically connected to the filaments of the respective left and right tube ends  12 ,  13  by means of electrically conducting starter wires  32  and  32 ′. Moreover, a capacitor  33  may be electrically connected in parallel with the starter switch bulb  29  as a radio frequency suppression device. The capacitor  33  is connected in parallel to the starter switch bulb via capacitor wires  34 . With this arrangement, the starter circuit operates to produce an electric arc in a manner known in the industry, which ignites the mercury vapor contained within the fluorescent tube  11  to produce ultra-violet light. The ultra-violet light is then converted by the phosphorous coating in the tube  11  to produce visible light. Once ignited by the starter circuit, gas ionization and light emission continues while electric power is supplied by the electric power source via the electrical contacts  25 ,  26 . 
     FIG. 2 shows an improvement upon the fluorescent bulb  10  shown in FIG.  1 . The improvement comprises a prophylactic sleeve, generally indicated at reference character  35 , which protectively surrounds the glass shell  30  of the starter switch bulb  29 . The sleeve  35  is particularly adapted to absorb impacts directed against the starter switch bulb  29 , and thereby provide a cushioning effect against damage or breakage. The prophylactic sleeve  35  preferably has a generally cylindrical configuration with a cylindrical sidewall  36 , an open upper end  37 , and an open lower end  38 . It is appreciated however, that the upper and lower ends  37 ,  38  may be opened or closed since it is estimated that the vast majority of impacts are directed laterally against and absorbed by the cylindrical sidewall  36 . The prophylactic  35  is preferably composed of a woven glass-fabric material, which is both heat resistant and provides electrical and mechanical insulation. 
     FIG. 3 shows a cross-sectional view of a portion of the switch cavity  24 , incorporating the prophylactic sleeve  35  of FIG.  2 . As can be seen in FIG. 3, the sleeve  35  preferably surrounds the starter switch bulb  29 , with the capacitor  33  located ulterior to the sleeve  35 . Alternatively, as can be seen in FIG. 4, the sleeve  35  may surround both the starter switch bulb  29  and the capacitor  33  together to provide combined protection from impacts. Furthermore, it is preferred that the sleeve  35  surround the starter switch bulb  29  in a snug manner enabling movement together as a single unit. However, a marginal clearance between the sleeve  35  and the glass-shell  30  of the starter switch bulb  29  is also contemplated. 
     In any case, the sleeve  35  operates to absorb impacts against the starter switch bulb  29  caused by the relative movements of components in the base cavity  15 , such as the starter switch bulb  29  and the capacitor  33 . Relative movements are possible due to the flexible wire-suspended arrangement of those components in the base cavity  15 . It is notable that, unlike the injected compound in the &#39;941 patent, the prophylactic sleeve  35  does not contact, stabilize, or fixedly secure the starter circuit components to the tube ends  12  or  13 . Rather the effects of relative movement of the components within the base  14  during rough service is ameliorated by absorbing the impacts experienced during use in rough service applications. It is appreciated that by utilizing the sleeve  35  to protectively surround the starter switch bulb  29  (and optionally the capacitor  33 ), this arrangement provides greater uniform coverage around the body of the starter switch bulb  29  without exposing any part and leaving it vulnerable to impacting contact. Moreover, the uniform coverage of the starter bulb provided by the sleeve  35  may prevent localized stresses from forming in the glass-shell  30  of the starter switch bulb  29 , unlike a cantilever attachment at one end of the starter switch bulb. 
     The present embodiments of this invention are thus to be considered in all respects as illustrative and not restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.