TECHNICAL FIELD OF THE INVENTION 
   The present invention is directed, in general, to ultraviolet lamps and, more particularly, to an absorptive barrier to prevent transmission of ultraviolet light within a designated region of an ultraviolet light source. 
   BACKGROUND OF THE INVENTION 
   Indoor air can include trace amounts of contaminants: e.g., dust, smoke, carbon monoxide, as well as volatile organic compounds generated or outgassed from the living space as a byproduct of our modern building methods. Particular offenders among these are the adhesives used for installation of carpets, flooring, insulation, etc. As indoor air flows through the return ducts of a heating, ventilation and air conditioning (HVAC) system, the air first encounters the system air filter which blocks the passage of particulate contaminants, and allows the return air to enter the portion of the HVAC system where it is heated, cooled, humidified, or dehumidified. A drawback to employing filters is that they simply block the passage of particulate contaminants and do not destroy them. However, they are essential in removing particulate contaminants from the air prior to conditioning. 
   It is known to use ultraviolet (UV) radiation alone in HVAC systems to kill airborne bacteria and viruses. Additionally, photocatalytic oxidation (PCO) air purification systems employ a photocatalytic coating, e.g., titanium dioxide, in combination with an activating photonic light source of a particular wavelength to destroy indoor airborne contaminants including volatile organic compounds such as formaldehyde, toluene, propanal, butene, and acetaldehyde. The system arrangement commonly includes one or more ultraviolet lamps, and a photocatalytic monolith, such as a honeycomb, coated with the photocatalytic coating. Titanium dioxide is well known as a photocatalyst in a fluid purifier to destroy such contaminants. When the titanium dioxide is illuminated with UV light, photons are absorbed by the titanium dioxide, promoting an electron from the valence band to the conduction band, thus producing a hole in the valence band and adding an electron in the conduction band. The promoted electron reacts with oxygen, and the hole remaining in the valence band reacts with water, forming reactive hydroxyl radicals. When a contaminant adsorbs onto the titanium dioxide photocatalyst, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances. 
   UV lamps in PCO applications are customarily tubular in form, and emit ultraviolet-wavelength photons within 360° around the longitudinal axis of the lamps. While UV light is extremely useful in the air purification and PCO applications, UV light is also very harmful to certain materials commonly found in the HVAC system, e.g., the air filter, electrical insulation, other polymers, etc. Exposure of these components to UV radiation results in early degradation and decreased system performance. 
   Accordingly, what is needed in the art is a device that protects vulnerable system components from UV light while not interfering in the air purification and PCO applications. 
   SUMMARY OF THE INVENTION 
   To address the above-discussed deficiencies of the prior art, the present invention provides, in one aspect, a heating, ventilating and air conditioning (HVAC) system, comprising a heat exchanger plenum having a surface located therein that is susceptible to degradation upon exposure to light, and a light bulb located within the plenum. In one embodiment, the light bulb has a side directed toward the surface and a light-absorptive barrier coupled to the side. The light-absorptive barrier is configured to reduce direct light transmission from the light bulb to the surface to thereby inhibit degradation of the surface. The invention further provides an HVAC system comprising a light bulb configured to emit photonic energy, and an absorptive barrier coupled to at least a portion of an outside of the bulb. The absorptive barrier is configured to substantially reduce transmission of the emitted photonic energy beyond the portion of the bulb. 
   The foregoing has outlined features of the present invention so that those skilled in the pertinent art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the pertinent art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the pertinent art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
       FIG. 1  illustrates a schematic view of a conventional heating, ventilation and air conditioning (HVAC) system having a photocatalytic oxidation (PCO) subsystem and constructed according to the principles of the present invention; 
       FIG. 2  illustrates an enlarged elevation view of the photocatalytic oxidation subsystem of  FIG. 1 ; 
       FIG. 3  illustrates a plan view of the photocatalytic oxidation subsystem of  FIG. 1 ; and 
       FIG. 4  illustrates an exploded isometric view of an alternative embodiment of a UV absorptive shield and UV light source constructed according to the principles of the present invention. 
   


   DETAILED DESCRIPTION 
   Referring initially to  FIG. 1 , illustrated is a schematic view of a conventional heating, ventilation and air conditioning (HVAC) system  100  having a photocatalytic oxidation (PCO) subsystem  110  and constructed according to the principles of the present invention. The photocatalytic oxidation (PCO) subsystem  110  may also be considered to be an air purifier. The HVAC system  100  comprises an outdoor portion  101 , i.e., above line  160 , and an indoor portion  102 , i.e., below line  160 . The outdoor portion  101  comprises a conventional electric motor-driven compressor  112  connected via a conduit  114  to a heat exchanger  116  disposed outdoors, typically, and comprising a refrigerant fluid primary condenser  116 . In the embodiment illustrated in  FIG. 1 , heat exchange between refrigerant fluid flowing through the condenser heat exchanger  116  and ambient air  119  is controlled by a fan  118  having plural fixed-pitch blades  118   a  and which is driven by a variable speed electric motor  120 . The electric motor  120  may be an electrically-commutated type operating on variable frequency and voltage AC electric power as supplied to the motor via a suitable controller  122 . Fan  118  propels a heat exchange medium, such as ambient outdoor air  119 , through the condenser heat exchanger  116  in a known manner. The condenser heat exchanger  116  may also operate with other forms of heat exchange media at controlled flow rates thereof. Control of heat exchange medium  119  flowing over condenser heat exchanger  116  may take other forms such as a constant speed variable pitch fan, air flow control louvers, or control of a variable flow of a liquid heat exchange medium. The condenser heat exchanger  116  is also operably connected to a conventional refrigerant fluid filter and dryer  124  disposed in a conduit  126  for conducting condensed refrigerant fluid to a conventional refrigerant fluid expansion device  140 . A temperature sensor  134 , disposed within a conditioned space  132  to be conditioned by the system  100 , is also operably connected to the controller  122 . Controlled/conditioned space  132 , as well as a return air path  155  from space  132 , are represented schematically in the drawing figures. 
   The indoor portion  102  comprises the controller  122 , a heat exchanger plenum  150 , a system filter  170 , the photocatalytic oxidation subsystem  110 , a drive motor  152 , a motor-driven blower  154 , the refrigerant fluid expansion device  140 , a heat exchanger  144 , and the temperature sensor  134 . While this discussion is directed to a photocatalytic oxidation subsystem, the conditions are substantially the same as for those installations wherein only a UV lamp is used to kill bacteria and viruses without benefit of a photocatalyst. Conduit  126  is operable to deliver refrigerant fluid to the conventional refrigerant fluid expansion device  140  and to the heat exchanger  144  or so called evaporator  144 , respectively. The expansion device  140  includes a remote temperature sensor  140   a  which is adapted to sense the temperature of refrigerant fluid leaving the heat exchanger  144  by way of a conduit  146 . Conduit  146  is commonly known as the suction line leading to the compressor  112  whereby refrigerant fluid in vapor form is compressed and recirculated through the system  100  by way of condenser heat exchanger  116 . Heat exchangers  116 ,  144  may be conventional multiple fin and tube type devices, for example. One who is of skill in the art will understand the functioning of the HVAC heretofore described. 
   The PCO subsystem  110 , within the heat exchanger plenum  150 , comprises a photocatalytic monolith  121 , a photocatalytic coating  121   a , and a photocatalytic light bulb  122 . The PCO subsystem  110  may comprise one or more ultraviolet lamps having an electrical circuit  125  therein, and the photocatalytic monolith  121 , such as a honeycomb, may have a titanium dioxide coating  121   a . In one embodiment, the photocatalytic light bulb  122  may comprise a UV light bulb. In a preferred embodiment, the photocatalytic light bulb  122  emits photons of a particular wavelength to cause the photons to be absorbed by the titanium dioxide coating  121   a , promoting an electron from the valence band to the conduction band, thus producing a hole in the valence band and adding an electron in the conduction band. The promoted electron reacts with oxygen, and the hole remaining in the valence band reacts with water, forming reactive hydroxyl radicals. When a contaminant adsorbs onto the titanium dioxide photocatalyst, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances. 
   Referring now to  FIG. 2 , illustrated is an enlarged elevation view of the photocatalytic oxidation subsystem  110  of  FIG. 1 . For simplicity, only one photocatalytic light bulb  122  is shown. In the presently depicted embodiment, the photocatalytic light bulb  122  is constructed according to the principles of the present invention, and comprises an ultraviolet lamp  210  having a transparent tubular bulb  220  with a longitudinal axis  225 , and a light-absorptive barrier  230 . Note that the light-absorptive barrier  230  is positioned on a side of the transparent tubular bulb  220  proximate a surface  171  of the system filter  170  and is thus between the ultraviolet lamp  210  and the system air filter  170 . For the purposes of this discussion, a light-absorptive barrier is defined as one that primarily absorbs photonic energy rather than one that reflects photonic energy, e.g., at least 51 percent of the photonic energy is absorbed versus not more than 49 percent of the photonic energy is reflected. In the illustrated embodiment, the light-absorptive barrier  230  is applied to an outside of the transparent tubular bulb  220 . 
   In those applications wherein a UV light source is used without benefit of a photocatalytic coating, other components of the HVAC system, e.g., electrical insulation, or other polymers, may be susceptible to damage from UV light. In those cases, the orientation of the UV light source would be such that the absorptive barrier  230  is positioned proximate the susceptible system component. 
   The electrical circuit  125  of the ultraviolet lamp bulb  210  emits photons  240  within 360° around the longitudinal axis  225 . Those photons  240  exiting the bulb  210  on a side opposite the barrier  240  impact the photocatalytic monolith  121  and cause the subsystem  110  to operate as intended to clean the air by oxidizing and removing contaminants. In one embodiment, the absorptive barrier  240  comprises at least a portion of the transparent tubular bulb  220 . In one embodiment, the absorptive barrier  240  comprises substantially 50 percent of the surface of the transparent tubular bulb  220 . In another embodiment, the absorptive barrier  240  comprises substantially 180° of the circumference of the transparent tubular bulb  220 . 
   Referring now to  FIG. 3 , illustrated is an enlarged plan view of the photocatalytic oxidation subsystem  110  of  FIG. 1 . In one embodiment, the absorptive barrier  230  comprises a material that absorbs UV light. In a preferred embodiment, the absorptive barrier  230  forms an arc  250  that ranges from about 180° to about 200° of a circumference of the transparent bulb  220 . In one embodiment, the absorptive barrier  230  comprises a film applied to an exterior of the transparent tubular bulb  220 . In one embodiment, the film  230  comprises a black paint that absorbs the photons  240 . The paint  230  may comprise: HiHeat Bar-B-Que Black paint, a product of Rust-Oleum® Corporation of Vernon Hills, Ill. In an alternative embodiment, the paint  230  may comprise a heat-resistant black paint product of Sheffield Bronze Paint Corp. of Cleveland, Ohio titled: Pot Belly Black, Item #906. 
   In one embodiment, the absorptive barrier  230  may comprise a UV absorptive film  230 . The UV absorptive film  230  may comprise UVShield™, a product of CPFilms Inc., of Filedale, Va. UVShield is a clear film that absorbs 99.9% of UVA and UVB manufactured by a patent pending process. Of course, UV light absorbing films may also have a color, i.e. silver, bronze, etc. Thus, UV light transmission is substantially reduced beyond the UV absorptive-covered portion of the transparent tubular bulb  220 . 
   Referring now to  FIG. 4 , illustrated is an exploded isometric view of an alternative embodiment of a UV absorptive shield  400  and UV light source  450  constructed according to the principles of the present invention. The UV absorptive shield  400  comprises a rigid semi-circular cover  410 , first and second clips  421 ,  422 , and an absorptive layer  430 . In a preferred embodiment, the semi-circular cover  410  is sized to fit snugly around the light source  450  which may be a UV lamp as previously described. The absorptive layer  430  may be applied to an inside of the cover  410 , or the cover  410  may be integrally molded of UV absorptive material. The first and second clips  421 ,  422  snap around the ends  451 ,  452  of the UV lamp  450  in a manner similar to household broom holders, holding the UV absorptive shield  400  to the UV lamp  450 . The first and second clips  421 ,  422  may be made of any suitable material having the requisite spring, e.g., metal, plastic, etc. UV radiation is thus prevented from passing outside of the UV lamp  450  in the portion where the lamp surface is covered with the substantially semi-circular cover  410 . 
   Thus, a light source has been described that prevents UV radiation from impinging on components of a HVAC system, e.g., the system filter, electrical insulation, etc., that could be damaged by the UV radiation. 
   Although the present invention has been described in detail, those skilled in the pertinent art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.
A heating, ventilating and air conditioning (HVAC) system, comprising a heat exchanger plenum having a surface located therein that is susceptible to degradation upon exposure to light, and a light bulb located within the plenum. In one embodiment, the light bulb has a side directed toward the surface and a light-absorptive barrier coupled to the side. The light-absorptive barrier is configured to reduce direct light transmission from the light bulb to the surface to thereby inhibit degradation of the surface. The invention further provides an HVAC system comprising a light bulb configured to emit photonic energy, and an absorptive barrier coupled to at least a portion of an outside of the bulb. The absorptive barrier is configured to substantially reduce transmission of the emitted photonic energy beyond the portion of the bulb.