OPTICAL FILM, LIGHT-DIFFUSING FILM, AND METHODS OF MAKING AND USING THE SAME CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of U.S. Patent Application Serial No. 10/852,916, filed on May 25, 2004, which is herein incorporated by reference in its entirety. BACKGROUND In backlight computer displays or other display systems, optical film (which may also be referred to as a sheet, layer, foil and the like) materials are commonly used, for example, to direct, diffuse, or polarize light. For example, in backlight displays, brightness enhancement films (BEFs) use prismatic structures on the surfaces thereof to direct light along a viewing axis (i.e., an axis normal (perpendicular) to the display). This enhances the brightness of the light viewed by the user of the display and allows the system to consume less power in creating a desired level of on-axis illumination. Such films may also be used in a wide range of other optical designs, such as in projection displays, traffic signals, and illuminated signs. In current displays systems, for example in liquid crystal displays (LCD), it is desirable to have light-diffusing films. Light-diffusing films describe a.broad class of articles that are used within LCD backlight systems to evenly distribute light to the viewer and hide potential defects generated by a light guide, while maintaining total transmission of light. In addition to these light management properties, these diffusing films need to satisfy certain properties related to their visual appearance in a backlight display system. In particular, these films should lay flat on other films in the system. Generally, when polycarbonate films are used in this application, their high coefficient of thermal expansion may cause portions of the film near the hot lamp to expand while film further from the lamp either does not expand or does not expand to a similar extent, resulting in waviness of these portions of the film, making the entire film unsuitable for use in a backlight display system. What is needed in the art is a light-diffusing polycarbonate film that minimizes or does not result in observable waviness under the heat of a lamp in backlight system. SUMMARY Disclosed herein are optical films, e.g., light-diffusing films, methods of making optical films, and liquid crystal display devices employing optical films. One embodiment of a method of making an optical film comprises heating the optical film comprising greater than or equal to 80 wt.% polycarbonate to a sufficient temperature to stretch the optical film, wherein the weight percent is based on a total weight of the optical film; and stretching the optical film, wherein a resulting stretched optical film has a linear CTE measured in a direction parallel to a stretching direction of less than or equal to 50 x 10"6 cm/cm/°C. One embodiment of a liquid crystal display device comprises an optical source; a light guide in optical communication with the light source; and a optical film comprising polycarbonate in optical communication with the light guide, wherein the optical film has a linear CTE, measured in a direction parallel to a stretching direction of the optical film, of less than or equal to 50 x 10"6 cm/cm/°C. One embodiment of an optical film comprises greater than or equal to 80 wt.% polycarbonate, wherein weight percent is based on a total weight of the optical film, and wherein the optical film has a linear CTE, measured in a direction parallel to a stretching direction of the optical film, of less than or equal to 50 x 10"6 cm/cm/°C. The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Refer now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike. Figure 1 is a perspective view of an exemplary embodiment of a backlight display device including a light-diffusing film. Figure 2 is a perspective view of an exemplary embodiment of a brightness enhancement film with prismatic surfaces. Figure 3 is a cross-sectional view of another exemplary embodiment of a brightness enhancement film with prismatic surfaces. Figure 4 is a cross-sectional view and schematic illustration of an exemplary embodiment of a light-diffusing film receptive of light and diffusing the light emanating therefrom. Figure 5 is a perspective view of an exemplary embodiment of two brightness enhancement films oriented at an angle with respect to each other. Figure 6 is a perspective view of an exemplary embodiment of a backlight display device including a plurality of brightness enhancement films and a plurality of light-diffusing films. Figure 7 is a schematic illustration of an exemplary embodiment of a method of stretching a light-diffusing film. DETAILED DESCRIPTION Disclosed herein are optical films, more particularly light-diffusing films (which may also be referred to as a "diffusers") comprising polycarbonate, wherein the light-diffusing films are capable of being employed in a liquid crystal display device (e.g., a backlight display device) without resulting in waviness of the light-diffusing film as a result of heat from an optical (light) source (e.g., a florescent lamp). Furthermore, it is noted that the optical films, more particularly the light-diffusing films are desirably unitary or monolithic films characterized by the absence of coatings. While it is noted that reference is made to a light-diffusing film throughout this disclosure, this reference is made merely for convenience in discussion and it is to be understood that the discussion is equally applicable to other types of optical films. The term "total" in relation to reflection is used herein to refer to the combined reflectance of all light from a surface. It is noted that the terms "bottom" and "top" are used herein, unless otherwise noted, merely for convenience of description, and are not limited to any one position or spatial orientation. The term "about" as used herein refers to values within ±10% of the specified value. It should further be noted that the terms "first," "second," and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Furthermore, all ranges disclosed herein are inclusive and combinable (e.g., ranges of "up to about 25 weight percent (wt.%), with about 5 wt.% to about 20 wt.% desired, and about 10 wt.% to about 15 wt.% more desired," is inclusive of the endpoints and all intermediate values of the ranges, e.g., "about 5 wt.% to about 25 wt.%, about 5 wt.% to about 15 wt.%," etc.). Several embodiments of backlight display devices are discussed hereunder with reference to individual drawing figures. One of skill in the art will easily recognize that many of the components of each of the embodiments are similar or identical to the others. Each of these elements is introduced in the discussion of Figure 1, but is not repeated for each embodiment. Rather, distinct structure is discussed relative to each figure/embodiment. Referring now to Figure 1, a perspective view of a backlight display device generally designated 100 is illustrated. The backlight display device 100 comprises an optical source 102 for generating light 104. A light guide 106 in optical communication with optical source 102 guides the light 104 by total internal reflection (TIR) of the light 104 within the light guide 106. A reflective film 108 in physical and/or optical communication with a first surface 110 of light guide 106 reflects the light 104 out of the light guide 106. A brightness enhancement film (BEF) 112 located in physical and/or optical communication with a second surface 114 of light guide 106 is receptive of the light 104 from the light guide 106. More particularly, the BEF 112 comprises a planar surface 116 in physical and/or optical communication with the second surface 114 of light guide 106, and a prismatic surface 118 in physical and/or optical communication with a light-diffusing film 120. Still further, it will be appreciated that the prismatic surfaces 118 may have a peak angle, a, a height, h, a pitch, p, and a length, 1 (see Figures 2 and 3). These parameters of peak angle, a, a height, h, a pitch, p, and a length, 1, may have prescribed values or may have values that are randomized or at least psuedo-randomized. Films with prismatic surfaces with randomized or pseudo-randomized parameters are described for example in U.S. Patent Application No. 10/150,958 to Olcazk filed on May 20,2002. The BEF 112 is receptive of the light 104 and acts to direct the light 104 in a direction that is substantially normal to the BEF 112 as indicated schematically by an arrow representing the light 104 being directed in a z-direction shown in Figure 1. The light-diffusing film 120 is receptive of the light 104 from the BEF 112 and diffuses (e.g., scatters) the light as illustrated schematically in Figure 4. The light 104 proceeds from the light-diffusing film 120 to a liquid crystal display (LCD) 122. Further, it is noted that in various embodiments a backlight display device may comprise a plurality of brightness enhancement films (BEF) and a plurality of light-diffusing films in optical communication with each other. The plurality of brightness enhancing films and light-diffusing films may be arranged in any configuration to obtain the desired results in the LCD. For example, the brightness enhancement films may be arranged in physical and/or optical communication with each other as illustrated in Figure 5. More particularly, a first BEF 212 comprises a first BEF planar surface 216 and a first BEF prismatic surface 218. A second BEF 224 comprises a second BEF planar surface 226 and a second BEF prismatic surface 228. The first BEF 212 and the second BEF 224 can be arranged such that the prismatic surfaces (218 and 228, respectively) are positioned at an angle with respect to one another, e.g., 90 degrees. Additionally, as briefly mentioned above, the arrangement and type of BEFs and light-diffusing films depends on the backlight display device in which they are employed. An increasingly common use of a backlight display device is for use in a notebook computer. While reference is made to a notebook computer throughout this disclosure, it is to be understood that one of skill in the art can readily use the light-diffusing films disclosed herein in other applications without undue experimentation. A backlight display device 300 for use in a notebook computer is illustrated in Figure 6. The backlight display device 300 comprises an optical source 302 for generating light 304. A light guide 306 in optical communication with optical source 302 guides the light 304 by total internal reflection of the light 304, as discussed above in relation to Figure 1. A reflective film 308 in physical and/or optical communication with a first surface 310 of light guide 306 reflects the light 304 out of the light guide 306. A bottom light-diffusing film 320 and a top light-diffusing film 330 are in optical communication with a first BEF 312 and a second BEF 324 disposed between the bottom light-diffusing film 320 and the top-diffusing film 330. The light 304 proceeds from the top light-diffusing film 330 to a liquid crystal display (LCD) 322. With regard to the embodiment illustrated in Figure 6, it is noted that the bottom light-diffusing film 320 functions primarily to enhance the uniformity of the light 304 and interacts with the other films (e.g., BEFs 312 and 324) to enhance on-axis luminance possible. Another function of the bottom light-diffusing film 320 is to hide optical imperfections that may be caused by the light guide 306. The top light-diffusing film 330 functions primarily to minimize glare and optical coupling (Newton Rings) between the BEFs (e.g., 312 and 324). In addition, the top light-diffusing film 330 may also function as a protective film for the BEF films (312, 324), thereby reducing the likelihood of fracturing or damaging the prismatic surfaces of the BEF films. Furthermore, it is noted that top light-diffusing films (e.g., 330), i.e., the light-diffusing film nearest to the liquid crystal display (e.g. 322), generally have a haze value of less than or equal to 85%, more particularly a haze value of less than or equal to 50%. Whereas, bottom light-diffusing films (e.g., 320), i.e., the light-diffusing film nearest the light guide (e.g., 306), generally have a haze value of greater than or equal to 90%, more particularly a haze value of greater than or equal to 95%. It is noted that the percent haze can be predicted and calculated from the following equation: Total Transmission wherein total transmission is the integrated transmission; and the total diffuse transmission is the light transmission that is scattered by the film as defined by ASTM D 1003. Optical source (e.g., 102, 302) may include any light source suitable to backlight a liquid crystal display (LCD) device, which includes both high-brightness and low brightness light sources. The high-brightness light source may include, but is not limited to, a cold cathode fluorescent lamp (CCFL), a fluorescent lamp, and the like. The low-brightness light source may include, but is not limited to, a light emitting diode (LED), and a cold cathode fluorescent lamp. Light guide (e.g., 106, 306) preferably comprises a material that assumes a low internal absorption of the light, including, but not limited to, an acrylic film and desirably transparent materials including acryl, PMMA (polymethylmethacrylate), polycarbonate, polyethylene, Selenium (Se), Silver Chloride (AgCl), and the like. The shape of the light guide may be in a shape suitable for use, such as a bar, a curved surface, a plate, a sheet, and the like. The light guide may be of a single piece or a lamination of a plurality of sheets. Reflective film (e.g. 108, 308) may be in any usable shape for reflecting light, e.g., a planar shape, such as a plate, sheet, and the like, wherein the reflective film comprises a reflective material. For example, suitable reflective materials include, but are not limited to, an aluminum deposited film, a silver deposited film, and the like. In other embodiments, the reflective film may comprise a thermoplastic material, e.g., Spectralon® (available from Labsphere, Inc.) or titanium-oxide pigmented Lexan® (available from General Electric Co.). As noted above, brightness enhancement films (e.g. 112) use prismatic structures to direct light along the viewing axis (i.e., normal to the display), which enhances the brightness of the light viewed by the user of the display and which allows the system to use less power to create a desired level of on-axis illumination. For example, the brightness enhancement film may include those materials discussed in U.S. Patent Application No. 20030108701 to Coyle et al. More specifically, the brightness enhancement film may comprise metal, paper, acrylics, polycarbonates, phenolics, cellulose acetate butyrate, cellulose acetate propionate, poly(ether sulfone), poly(methyl methacrylate), polyurethane, polyester, poly(vinylchloride), polyethylene terephthalate, and combinations comprising at least one of the foregoing. A light-diffusing film (e.g., 120) comprising polycarbonate is capable of being employed in a backlight display device without resulting in waviness of the light-diffusing film as a result of heat from an optical (light) source. Various techniques may be utilized to obtain films with light-diffusing capabilities. For example, physical modifications to the films may result in imprinting a texture to the surface of the film to diffuse light (e.g., textured light-diffusing films). As will be discussed in greater detail, it is desirable to texture both a top and bottom surface of the film. In other embodiments, light-diffusing particles may be imbedded into the film to give the film light-diffusing properties (e.g., bulk light-diffusing films). In yet other embodiments, a combination of both methods may be used, i.e., both imprinting a texture on the surface of the film and imbedding a light-diffusing particle in the film. In an embodiment, the light-diffusing film comprises polycarbonate, an anti-static material, and optionally, light-diffusing particles. The light-diffusing film comprises greater than or equal to 80 wt.% polycarbonate, and more particularly greater than or equal to 90 wt.% polycarbonate, wherein weight percents are based on total weight of the light-diffusing film. For example, in an embodiment, the light-diffusing film may comprises about 93 wt.% to about 99.6 wt.% polycarbonate; about 0.4 wt.% to about. 7 wt.% anti-static material, more specifically, about 0.4 wt.% to about 2 wt.% antistatic material; and optionally up to about 7 wt.% light-diffusing particles, more specifically, about 2 wt.% to 7 wt.%, wherein weight percents are based on total weight of the light-diffusing film. More specifically, the light-diffusing film may include those disclosed in U.S. Patent Application No. 10/787,158, which is herein incorporated by reference. The anti-static material of the light-diffusing film comprises a sufficient anti-static material in an amount sufficient to impart anti-static properties to the film. For example the anti-static material may comprise phosphonium sulfonate. More particularly, in an embodiment, the anti-static material is that described in U.S. Patent 6,194,497 to Henricus et al. More specifically, the phosphonium sulfonate can be a fluorinated phosphonium sulfonate and comprises a fluorocarbon containing an organic sulfonate anion and an organic phosphonium cation. Examples of such organic sulfonate anions include, but are not limited to, perfluoro methane sulfonate, perfluoro butane sulfonate, perfluoro hexane sulfonate, perfluoro heptane sulfonate, and perfluoro octane sulfonate. Examples of the phosphonium cation include, but are not limited to, aliphatic phosphonium such as tetramethyl phosphonium, tetraethyl phosphonium, tetrabutyl phosphonium, triethylmethyl phosphonium, tributylmethyl phosphonium, tributylethyl phosphonium, trioctylmethyl phosphonium, trimethylbutyl phosphonium trimethyloctyl phosphonium, trimethyllauryl phosphonium, trimethylstearyl phosphonium, triethyloctyl phosphonium and aromatic phosphoniums such as tetraphenyl phosphonium, triphenylmethyl phosphonium, triphenylbenzyl phosphonium, tributylbenzyl phosphonium. More specifically, the fluorinated phosphonium sulfonate may be obtained by any combination of any of these organic sulfonate anions and organic cations. Furthermore, even more specifically, the phosphonium sulfonate employed herein can be a fluorinated phosphonium sulfonate having the general formula: {CF3(CF2)n(S03)}e {P(R,)(R2)(R3)(R4)}