You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     The invention relates to a covering for a suspended ceiling grid system, and more particularly, to a cap to retrofit onto an existing suspended ceiling grid system. 
     BACKGROUND OF THE INVENTION 
     Ceiling grid systems for supporting tile panels, such as acoustical ceiling tiles, are used extensively in both new and remodeled building and room structures. Grid systems typically consist of main runners and cross-tees, having lateral supporting shoulders, that are arranged perpendicular to each other to form a rectangular pattern. After the grid is installed, the tile panels are placed onto the supporting shoulders of the runners and cross-tees. Such a grid system offers many advantages such as increasing a room&#39;s energy efficiency, improving a room&#39;s acoustics, enhancing the aesthetic value of a room, providing a means for lowering a ceiling, and allowing for the installation of electrical fixtures, pipes and duct work. 
     Ceiling grid systems are relatively inexpensive and easy to install as compared to a plaster ceiling. As a consequence, there is a continuing need to improve on the design and integrity of grid systems, particularly in light of the fact that many such systems are installed in commercial buildings requiring years of service, or installed by the do-it-yourself home owner. 
     In particular, there is a need to extend the life of the ceiling grid system. After a period of use, a suspended ceiling grid system, such as made from metal, may begin to degrade in that the components may start to rust or to flake, chip or peel paint or may be damaged such as by denting. Further, the color of the grid system as seen by a room&#39;s occupant may become discolored or faded over time. For example, in a food processing plant, flaking paint from a suspended ceiling grid system may be a safety and/or health hazard. In general, such a degraded ceiling grid system is also not aesthetically pleasing. Typically, such a degraded ceiling grid system had to be either repainted or removed/replaced with a new ceiling grid system, both at a high cost in labor and materials. Repainting may also be a temporary fix in that it is likely the paint will begin to flake or peel again. 
     Aesthetically, the color of a suspended ceiling grid system as seen by a room&#39;s occupants may also be outdated or there may be a need to change the decor of the room. Typically, suspended ceiling grid systems would have to be either repainted or replaced with the new desired colored ceiling grid system in order to change the color of the ceiling, again both at a high cost in labor and materials. 
     Accordingly, there exists a need for a device to cover a suspended ceiling grid system, such as an existing metal ceiling grid system, to change or retroactively change the appearance of the grid system without having to repaint or replace the grid system. 
     SUMMARY OF THE INVENTION 
     The invention provides a covering or cap for a suspended ceiling grid system. The covering is particularly suited to fit or retrofit onto an existing installed suspended ceiling grid system. The covering is preferably a plastic cap that can be snap fit onto the main runners and cross-tees of the grid system. The covering is comprised of an elongate body having a flange and a lip which are opposed and which facilitate easy assembly and disassembly from the suspended ceiling grid system. 
     It is a feature of the present invention to provide a covering for a suspended ceiling grid system. 
     It is another feature of the present invention to provide a covering for a suspended ceiling grid system to change the appearance of such a grid system. 
     It is another feature of the present invention to provide a covering for an installed ceiling grid system to change the appearance of such a grid system. 
     It is another feature of the present invention to provide a covering for an installed metal suspended ceiling grid system to change the appearance of such a grid system. 
     It is another feature of the present invention to provide a covering for a suspended ceiling grid system to change the color of the visible portions of the main runners and cross-ties. 
     It is another feature of the present invention to provide a covering for a degraded suspended ceiling grid system. 
     It is another feature of the present invention to provide a covering for an installed suspended ceiling grid system to eliminate rust, paint or the like from peeling or flaking from the grid system. 
     It is another feature of the present invention to provide a covering for an installed suspended ceiling grid system to cover the discolored or faded portion of the system visible to a room&#39;s occupant. 
     It is another feature of the present invention to provide a covering for a suspended ceiling grid system that is easy to install. 
     It is another feature of the present invention to provide a covering for a suspended ceiling grid system that is more cost effective than repainting or replacing the grid system. 
     It is another feature of the present invention to provide a covering for an installed suspended ceiling grid which can be snap fit onto the installed grid system. 
     It is another feature of the present invention to provide a cap for a suspended ceiling grid system that includes an elongate body having a flange and a lip that engage the grid system. 
     It is another feature of the present invention to provide a covering for a suspended ceiling grid system that is made from an extruded plastic. 
    
    
     Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end view of a covering for a suspended ceiling grid system embodying the invention; 
     FIG. 2 is a top view of the covering; 
     FIG. 3 is a cross-sectional end view of a runner of a suspended ceiling grid system; 
     FIG. 4 is a cross-sectional end view of the covering partially installed onto the runner of FIG. 3; and 
     FIG. 5 is a cross-sectional end view of the covering fully installed onto the runner of FIG.  3 . 
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is shown in FIG. 1 a covering or cap  10  for a suspended ceiling grid system embodying the invention. The covering  10  includes a central web portion  12  having two edges. A flange  14  is preferably integral with one edge and a lip  16  is preferably integral with the other edge. The flange  14  and the lip  16  are opposed and extend inwardly over the web portion  12  toward one another. The flange  14  cooperates with the web portion  12  to define a channel  18 . The channel  18  is configured so as to house a portion of a main runner or a cross-tee as will be more fully explained below. The lip  16  cooperates with the web portion  12  to define a channel  20 . The channel  20  is configured so as to house a portion of a main runner or a cross-tee as will be more fully explained below. At this point, it should be noted that the flange  14  and the lip  16  have lengths that extend inwardly over the web portion  12  and toward each other, with such lengths being unequal. 
     Preferably, the covering  10  is extruded from a plastic such as PVC. The longitudinal length of the covering  10  can be varied to accommodate varying dimensions of suspended ceiling grid systems or the covering  10  can be provided in bulk coiled form then cut by the installer to fit in a particular installation. Further, the covering  10  can be produced in varying colors to accommodate varying color schemes in the environment into which the covering  10  will be installed. 
     Referring now to FIG. 2, the covering  10  preferably includes notches  22  along its longitudinal length. The notches  22  allow perpendicularly adjacent coverings  10  to mate at an intersection of a main runner and a cross-tee, as is conventional in the art. 
     Turning now to FIG. 3, a runner  24 , such as a main runner or a cross-tee, of a typical suspended ceiling grid system is shown. The runner  24  includes two sheets  26  and  28 , typically metal, that are bent or folded to the configuration shown in FIG.  3 . The sheet  26  is folded to a generally T-shaped configuration and the sheet  28  is bent around the T-shaped portion  30  of the sheet  26  so as to be generally C-shaped. Conventionally, a bottom face  32  of the sheet  28  had been painted or coated as this would have been the face that was visible to occupants of the room where it will be installed. It is this painting or coating that could degrade with time and flake, peel or rust. The runner  24  includes edges  34  and  36 . 
     Turning now to the installation of the covering  10  and FIG. 4, the edge  34  of the runner  24  is positioned in the channel  18  of the flange  14 . Upward pressure is then applied to the covering  10  on the web portion  12  near the lip  16  in the direction of the arrow in FIG. 4 such as by an installer&#39;s thumb. The upward pressure deforms the lip  16  enough to allow the covering  10  to snap into its installed position as is shown in FIG. 5 wherein the edge  36  is housed in the channel  20 . In its installed position, the covering  10  is securely but removeably positioned on the runner  24  by the flange  14  and the lip  16 . It should be noted that the ease of installation of the covering  10  onto the runner  24  is particularly advantageous when installing the covering  10  on an existing suspended grid system where the installer is working overhead to install the covering  10 . The snap fit covering  10  is both time efficient and installer friendly. If necessary, the covering  10  can be removed from the runner  24  by the application of downward pressure in the direction of the arrow in FIG.  5 . 
     Turning back to FIG. 1, the flange  14  has a first portion  40  having a height dimension H 1  and a second portion  42  having a length dimension L 1 . The lip  16  has a first portion  44  having a height dimension H 2  and a second portion  46  having a length dimension L 2 . The height dimension H 1  and H 2  of the portions  40  and  44 , respectively, are preferably equal so as to accommodate the typically uniform height dimension of the edges  34  and  36  of the runner  24 . However, and as noted above, the length dimension L 1  and L 2  of the portions  42  and  46 , respectively, are not equal. This is to enable the releasable snap fit action of the covering  10  onto the runner  24 . 
     More specifically, the length dimension L 2  of the first portion  44  of the lip  16  must enable the releasable snap fit action for ease of installation of the covering  10 . The length dimension L 2  is chosen so that the first portion  42  of the lip  16  is able to travel upwardly in the direction of the arrow in FIG.  4  and outwardly in a direction away from the web portion  12  thus allowing the lip  16  to travel around the edge  36 . The lip then deforms or snaps back to its original non-deformed position when it has cleared the edge  36  to result in the edge  36  being housed in the channel  20 . 
     An advantage of the covering  10  being preferably manufactured of a plastic is that health and safety regulations may be more easily met as opposed to repainting a degraded grid system. 
     Although particularly suited for a retrofit application, the covering  10  can also be provided with new or uninstalled ceiling grid systems to provide the consumer greater color options. For example, a new ceiling grid system could be sold in a standard color, such as white, then the consumer could select a covering  10  for the grid system in a color suitable for its installed environment.

Summary:
A covering for a suspended ceiling grid system, the covering is particularly suited to be retrofitable onto an installed suspended ceiling grid system, the covering is preferably a plastic cap that can be snap fit onto the main runners or cross-tees of the installed suspended ceiling grid system, and the covering is comprised of an elongate body having an opposed flange and lip which facilitate easy assembly and disassembly from a suspended ceiling grid system.