Abstract:
Disclosed is an optical film. The optical film includes:
       a base film including a material having optical transmittance and a thermal resistance;   a matrix layer disposed on the base film and comprising a fluorescent material; and   a protective layer disposed on the matrix layer and including a material having adhesive property.

Description:
[0001]    The present application claims priority under 35 U.S.C. §119(e) of Korean Patent Applications Nos. 10-2009-0099292, 10-2009-0099293 and 10-2009-0099294 filed on Oct. 19, 2009 and 10-2010-0033023 filed on Apr. 10, 2010, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    This embodiment relates to a lighting device. 
         [0004]    2. Description of the Related Art 
         [0005]    A light emitting diode (hereinafter, referred to as LED) is a semiconductor element for converting electric energy into light. As compared with existing light sources such as a fluorescent lamp and an incandescent electric lamp and so on, the LED has advantages of low power consumption, a semi-permanent span of life, a rapid response speed, safety and an environment-friendliness. For this reason, many researches are devoted to substitution of the existing light sources with the LED. The LED is now increasingly used as a light source for lighting devices, for example, various lamps used interiorly and exteriorly, a liquid crystal display device, an electric sign and a street lamp and the like. 
       SUMMARY 
       [0006]    One embodiment is an optical film. The optical film includes: 
         [0007]    a base film including a material having optical transmittance and a thermal resistance; 
         [0008]    a matrix layer disposed on the base film and comprising a fluorescent material; and 
         [0009]    a protective layer disposed on the matrix layer and including a material having adhesive property. 
         [0000]    Another embodiment is an optical film. The optical film includes: 
         [0010]    a base film having a thickness between about 10 μm and about 500 μm; 
         [0011]    a matrix layer disposed on the base film and comprising a fluorescent material and having a thickness between about 20 μm and about 500 μm; and 
         [0012]    a protective layer having an optical transmittance on about 80% and/or a viscosity between about 2,000 cp and about 10,000 cp disposed on the matrix layer. 
         [0000]    Further another embodiment is an optical film. The optical film includes: 
         [0013]    a light emitting chip; and 
         [0014]    an optical film including at least one sort of a fluorescent material excited by light emitted from the light emitting chip, wherein light passing through the optical film has a color rendering index (CRI) between 85 and 100. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross sectional view of an optical film according to a first embodiment. 
           [0016]      FIGS. 2 to 5  are views for describing a method fabricating for the optical film according to the first embodiment. 
           [0017]      FIG. 6  is a cross sectional view of an optical film according to a second embodiment. 
           [0018]      FIG. 7  is a flowchart showing a method for fabricating the optical film according to the first embodiment. 
           [0019]      FIG. 8  is a cross sectional view of an optical film according to a third embodiment. 
           [0020]      FIGS. 9 to 11  are views for describing a method for fabricating the optical film according to the third embodiment. 
           [0021]      FIG. 12  is a flowchart showing a method fabricating for the optical film according to the third embodiment. 
           [0022]      FIG. 13  is a view showing a light emitting device according to the embodiment. 
           [0023]      FIG. 14  is a table showing kinds and amounts of fluorescent materials based on color temperatures of the light emitting device. 
           [0024]      FIGS. 15 to 20  are graphs showing a color rendering index (CRI) change of the light emitting device. 
           [0025]      FIG. 21  is a view showing a light unit including the light emitting device. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. 
         [0027]    It will be understood that when an element is referred to as being ‘on’ or “under” another element, it can be directly on/under the element, and one or more intervening elements may also be present 
       First Embodiment 
       [0028]      FIG. 1  is a cross sectional view of an optical film  1  according to a first embodiment. 
         [0029]    Referring to  FIG. 1 , the optical film  1  includes a base film  10 , a matrix layer  20  on the base film  10 , a protective layer  30  on the matrix layer  20 , a protective film  40  on the protective layer  30 , an adhesive member  50  on the protective film  40  and a release film  60  on the adhesive member  50 . 
         [0030]    The matrix layer  20  includes a fluorescent material. The fluorescent material is excited by a first light emitted by a light source and emits a second light. 
         [0031]    That is, the optical film  1  has a function capable of changing the wavelength of light emitted from the light source and externally emitting the light. 
         [0032]    Therefore, the optical film  1  is applied to light sources of various lighting devices, a backlight unit, a light emitting element, a display device and the like and is used to generate light having various wavelengths or to improve a color rendering index (CRI) of the light source. 
         [0033]    Hereinafter, components of the optical film  1  will be described in detail. 
         [0034]    It is desired that the base film  10  is made of a resin material having an excellent optical transmittance and a thermal resistance. For example, the base film  10  is made of materials selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), an acrylic resin, polycarbonate (PC), polystyrene (PS) and polymethyl methacrylate (PMMA), etc. 
         [0035]    More specifically, the material of the base film  10  is determined based on the use of the optical film  1 . For example, if a high optical transmittance is required, the PET having an optical transmittance over 90% can be used. If a thermal resistance and chemical resistance are required, the base film  10  can be made of polycarbonate. However, there is no limit to the material of the base film  10 . 
         [0036]    The base film  10  has a thickness within a range, for example, between 10 μm and 500 μm, and preferably, between 20 μm and 30 μm. Because while the base film  10  having a thickness between 10 μm and 500 μm is easy to handle and has an excellent optical transmittance, base film  10  having a thickness between 20 μm and 30 μm is easier to handle and has a more excellent optical transmittance. However, there is no limit to the thickness of the base film  10 . 
         [0037]    The matrix layer  20  is formed on the base film  10 . 
         [0038]    It is desired that the matrix layer  20  is made of a material having an excellent optical transmittance, a viscosity, a curing temperature and so on because the optical film  1  may be applied to a light source emitting light at the high temperature and is required to maintain the excellent optical transmittance, a viscosity and hardness even at a high temperature. 
         [0039]    More specifically, since the matrix layer  20  has an optical transmittance over 80%, is cured at a temperature lower than 120° C. and has a viscosity over 3,000 cp, the matrix layer  20  can be made of a material more adhesive to the base film  10 . For example, the matrix layer  20  is made of at least one of a resin material and a silicon material, preferably, the silicone resin. 
         [0040]    The matrix resin film  20  has a thickness within a range between 20 μm and 500 μm, and preferably, between 30 μm and 50 μm. The matrix layer  20  having such a thickness allows the following fluorescent material, a diffusing agent and an antifoaming agent to be easily mixed therewith, allows light to stably transmit and is readily applied on the base film  10 . 
         [0041]    The matrix layer  20  includes a fluorescent material. The fluorescent material is, for example, mixed with the liquefied matrix layer  20  and is agitated by using an agitator. As such, the fluorescent material is included in the matrix layer  20 . 
         [0042]    The fluorescent material is excited by a first light emitted by a light source and emits a second light. For example, at least one of a silicate based material, a sulfide based material, a YAG series and a TAG based material is used as the fluorescent material. 
         [0043]    The fluorescent material is excited by the first light emitted from a light source and includes at least one of yellow, red, green and blue fluorescent materials, each of which emits yellow, red, green and blue lights respectively. There is no limit to the kind of the fluorescent material. 
         [0044]    Meanwhile, CaS:Eu that is a kind of inorganic fluorescent material of the sulfide based material is representatively used to emit deep red light. At least one of SrS:Eu and MgS:Eu of the sulfide based material is used as an orange color fluorescent material. SrGa 2 S 4 : Eu 2 + of the sulfide based material is used as a green fluorescent material. 
         [0045]    The matrix layer  20  includes the fluorescent materials having various kinds and amounts in accordance with a light source to which the optical film  1  is applied. 
         [0046]    For example, when the optical film  1  is applied to white light source, the matrix layer  20  includes green and red fluorescent materials. With respect to 100 weight percent of the matrix layer  20 , the matrix layer  20  includes 1 to 60 weight percent of the green fluorescent material and 1 to 60 weight percent of the red fluorescent material. 
         [0047]    In addition, when the optical film  1  is applied to blue light source, the matrix layer  20  includes green, yellow and red fluorescent materials. With respect to 100 weight percent of the matrix layer  20 , the matrix layer  20  includes 1 to 60 weight percent of the green fluorescent material, 1 to 60 weight percent of the yellow fluorescent material and 1 to 60 weight percent of the red fluorescent material. 
         [0048]    As such, the kind and amount of the fluorescent material included in the matrix layer  20  varies depending on the kind of a light source. There is no limit to the kind and amount of the fluorescent material. 
         [0049]    Meanwhile, the matrix layer  20  further includes at least one of the diffusing agent, the antifoaming agent, an additive and a curing agent. 
         [0050]    The diffusing agent scatters and diffuses light incident on the matrix layer  20 . The diffusing agent includes, for example, at least one of SiO 2 , TiO 2 , ZnO, BaSO 4 , CaSO 4 , MgCO 3 , Al(OH) 3 , synthetic silica, glass beads and diamond. However, there is no limit to the kind of the diffusing agent. 
         [0051]    The particle of the diffusing agent is determined to have an appropriate size for diffusion of light, for example, a diameter of from 5 μm to 7 μm. 
         [0052]    The antifoaming agent removes the foams in the matrix layer  20  and improves the reliability of the optical film  1 . Particularly, the antifoaming agent is able to solve the problem of the foams generated during the process of applying the matrix layer  20  on the base film  10  by a screen printing method. 
         [0053]    The antifoaming agent includes at least one of octanol, sikeulroheksanol, ethylene glycol or various surface active agents. However, there is no limit to the kind of the antifoaming agent. 
         [0054]    The curing agent cures the matrix layer  20 . The additive is used for uniformly dispersing the fluorescent material in the matrix layer  20 . 
         [0055]    The protective layer  30  is formed on the matrix layer  20 . 
         [0056]    The protective layer  30  is made of a resin material or/and a silicon material having an excellent optical transmittance, a thermal resistance and adhesiveness. 
         [0057]    In particular, it is desired that the protective layer  30  is made of a material more adhesive to the protective film  40  formed on the protective layer  30 . For example, the protective layer  30  is formed of a silicone resin having an optical transmittance over 80%, an excellent thermal resistance and adhesiveness. 
         [0058]    The protective layer  30  has a thickness within a range, for example, between 20 μm and 50 μm. However, there is no limit to the thickness of the protective layer  30 . 
         [0059]    If the protective film  40  is formed directly on the matrix layer  20 , there is an insufficient adhesive strength between the matrix layer  20  and the protective film  40 . As a result, the two layers are separated from each other and water permeates a space between the two layers. This may be a factor causing the reliability of the optical film to be degraded. 
         [0060]    Accordingly, in the embodiment, the protective layer  30  is formed between the matrix layer  20  and the protective film  40 , allowing the matrix layer  20  to be strongly adhered to the protective film  40  and improving the reliability of the optical film  1 . 
         [0061]    More specifically, first, the protective layer  30  in a B-stage state is applied on the matrix layer  20 . Then after the protective film  40  is adhered on the protective layer  30  in a B-stage state, the protective layer  30  is cured. Consequently, the protective film  40  is securely adhered on the protective layer  30  and the reliability of the optical film  1  is improved. 
         [0062]    Moreover, when the protective layer  30  is formed in the same manner as that of the embodiment, there is an effect of protecting the fluorescent material included in the matrix layer  20 . That is, the protective layer  30  performs a function of mitigating the transfer of the heat generated by the light source to the fluorescent material, allowing the fluorescent material to be less degraded by the heat. Particularly, since red fluorescent material is generally vulnerable to heat, it is possible to more surely protect the fluorescent material by means of the protective layer  30 . 
         [0063]    The protective film  40  is formed on the protective layer  30 . The protective film  40  protects the matrix layer  20 , improving the reliability of the optical film  1 . 
         [0064]    The protective film  40  is made of the same material as that of the base film  10 . For example, the protective layer  40  is made of materials selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), an acrylic resin, polycarbonate (PC), polystyrene (PS) and polymethyl methacrylate (PMMA), etc. 
         [0065]    In addition, the protective film  40  has a thickness within a range, for example, between 10 μm and 500 μm, and preferably, 25 μm. 
         [0066]    The adhesive member  50  is formed on the protective film  40 . 
         [0067]    The adhesive member  50  includes a body layer  51 , a first adhesive layer  52   a  and a second adhesive layer  52   b.    
         [0068]    The second adhesive layer  52   b  is formed between the body layer  51  and the protective film  40  and allows the two layers to be adhered to each other. 
         [0069]    Additionally, the first adhesive layer  52   a  is formed on the body layer  51  and allows the optical film  1  to be adhered to an external light source. 
         [0070]    The adhesive member  50  can be separately provided and adhered to the protective film  40 . Otherwise, the adhesive member  50  can be formed by stacking the second adhesive layer  52   b , the body layer  51  and the first adhesive layer  52   a  in the order specified. There is no limit to a method of forming the adhesive member  50 . When the adhesive member  50  is not required, the adhesive member  50  may not be formed. There is no limit to a method of forming the adhesive member  50 . 
         [0071]    The release film  60  is formed on the adhesive member  50 . The release film  60  prevents the first adhesive layer  52   a  from being dried by air, etc., and from losing the adhesive strength. After removing the release film  60 , the optical film  1  is adhered to a light source and the like. 
         [0072]    Hereinafter, a method for fabricating the optical film  1  will be described in detail. However, the repetitive description of the foregoing description will be briefly described or omitted. 
         [0073]      FIGS. 2 to 5  show a method for fabricating the optical film  1 .  FIG. 7  is a flowchart showing a method for fabricating the optical film  1 . 
         [0074]    Referring to  FIG. 2 , the base film  10  is provided (S 101  of  FIG. 7 ). The matrix layer  20  is formed on the provided base film  10  (S 102  of  FIG. 7 ). 
         [0075]    The material and size of the base film  10  is determined according to the kind of a light source to which the optical film  1  is applied. 
         [0076]    The matrix layer  20  is formed on the base film  10 . The matrix layer  20  is formed, for example, by forming a liquefied matrix resin formed through the mixture and agitation of a silicone resin and a fluorescent material and by applying the liquefied matrix resin on the base film  10 . 
         [0077]    The matrix layer  20  is formed, for example, by applying and curing the liquefied matrix resin on the base film  10  through use of a screen printing method, a slit coating method and a roll coating method, etc. The matrix layer  20  is dried and cured at a temperature of about 100° C. by using a microwave and an infrared drier, etc., or is cured by adding the curing agent. 
         [0078]    Referring to  FIGS. 3 and 4 , the protective layer  30  is formed on the matrix layer  20  (S 103  of  FIG. 7 ). The protective film  40  is formed on the protective layer  30  (S 104  of  FIG. 7 ). 
         [0079]    The protective layer  30  in a B-stage state is applied on the matrix layer  20 . Then after the protective film  40  is adhered on the protective layer  30  in a B-stage state, the protective layer  30  is cured. Consequently, the protective film  40  is securely adhered on the protective layer  30  and the reliability of the optical film  1  is improved. 
         [0080]    The protective layer  30  is cured by adding the curing agent or is dried at a temperature of about 100° C. by using a microwave and an infrared drier, etc. 
         [0081]    The protective layer  30  is made of a resin material or/and a silicon material having an excellent optical transmittance, a thermal resistance and adhesiveness. The protective layer  30  has a thickness within a range between 20 μm and 50 μm. 
         [0082]    The protective film  40  is made of the same material as that of the base film  10 . The protective film  40  has a thickness within a range, for example, between 10 μm and 500 μm. 
         [0083]    Referring to  FIG. 5 , the optical film  1  according to the embodiment is provided by forming the adhesive member  50  and the release film  60  on the protective film  40  (S 105  of  FIG. 7 ). 
         [0084]    The adhesive member  50  can be separately provided and adhered to the protective film  40 . Otherwise, the adhesive member  50  can be formed by stacking the second adhesive layer  52   b , the body layer  51  and the first adhesive layer  52   a  in the order specified. There is no limit to a method of forming the adhesive member  50 . When the adhesive member  50  is not required, the adhesive member  50  may not be formed. There is no limit to a method of forming the adhesive member  50 . 
         [0085]    The release film  60  prevents the first adhesive layer  52   a  from being dried by air, etc., and losing the adhesive strength. After removing the release film  60 , the optical film  1  is adhered to a light source and the like. 
         [0086]    In the meantime, for the purpose of improving the reliability of the optical film  1 , it is possible to perform a post-treatment process of heating the optical film  1  at a temperature of from 50° C. to 100° C. for one hour to twenty four hours. 
       Second Embodiment 
       [0087]    Hereinafter, an optical film  2  according to a second embodiment and a method for fabricating the same will be described in detail. In the description of the second embodiment, repetitive descriptions thereof will be omitted. 
         [0088]      FIG. 6  is a cross sectional view of the optical film according to the second embodiment. The optical film  2  according to the second embodiment is different from the optical film  1  according to the first embodiment in that the optical film  2  does not include the protective film. 
         [0089]    Referring to  FIG. 6 , the optical film  2  includes a base film  10 , a matrix layer  20  on the base film  10 , a protective layer  30  on the matrix layer  20 , an adhesive member  50  on the protective layer  30  and a release film  60  on the adhesive member  50 . 
         [0090]    The adhesive member  50  is formed directly on the protective layer  30 . In other words, the protective film shown in the first embodiment is not formed. 
         [0091]    Since the separate protective film is not formed, the protective layer  30  is formed thicker than that of the first embodiment. Therefore, the reliability of the optical film  2  can be obtained. For example, the protective layer  30  has a thickness within a range between 20 μm and 100 μm. There is no limit to the thickness of the protective layer  30 . 
       Third Embodiment 
       [0092]      FIG. 8  is a cross sectional view of an optical film  3  according to a third embodiment. 
         [0093]    Referring to  FIG. 8 , the optical film  3  includes a base film  10 , a matrix layer  20  on the base film  10 , a viscous layer  30   a  on the matrix layer  20 , and a release film  60  on the viscous layer  30   a.    
         [0094]    Since the base film, the matrix layer and the release film have been already described in the optical film of the first embodiment, descriptions thereabout will be omitted. 
         [0095]    The viscous layer  30   a  is formed on the matrix layer  20 . The viscous layer  30   a  has an excellent optical transmittance and thermal resistance, and particularly is made of a resin material or/and a silicon material having an excellent viscosity. 
         [0096]    For example, the viscous layer  30   a  may be formed of a silicone resin, more preferably, a solvent type silicone resin including toluene. Since the silicone resin including the toluene has not only excellent viscosity but also high optical transmittance, another adhesive member for adhering the optical film  2  to a light source, etc., is not required. 
         [0097]    In other words, through the formation of the viscous layer  30   a , it is possible to simplify the manufacturing process of the optical film  1 , to allow the optical film  2  to be thinner, and to hereby reduce the amount of loss of light transmitting the optical film  2 . The optical transmittance of the silicone resin including the toluene may be at least more than 90%, and viscosity of the silicone resin may be between 2,000 cp (centipoises) and 10,000 cp. 
         [0098]    Meanwhile, it is preferable that the thickness of the viscous layer  30   a  is, for example, from 20 μm to 100 μm. 
         [0099]    The viscous layer  30   a  having such a thickness functions to absorb heat which is generated by the light source and is transferred to the fluorescent material included in the matrix layer  20 , thus reducing the degradation of the fluorescent material. In particular, since a red fluorescent material is vulnerable to heat, the red fluorescent material can be more clearly protected by the viscous layer  30   a.    
         [0100]    Regarding the viscous layer  30   a  including volatile toluene, after the viscous layer  30   a  is formed in a state of B-stage on the matrix layer  20 , the viscous layer  30   a  can be cured by heating and drying through the use of a microwave, an infrared drier, etc., instead of a separate curing agent. Further, the viscous layer  30   a  can be cured by adding the curing agent. However, there is no limit to a method of curing the viscous layer  30   a.    
         [0101]    The release film  60  is formed on the viscous layer  30   a . The release film  60  is able to prevent the viscous layer  30   a  from being exposed to the air, etc., and losing an adhesive strength. The optical film  2  can be adhered to a light source and the like after removing the release film  60 . 
         [0102]    Hereinafter, a method for fabricating the optical film  3  will be described in detail. However, the repetitive description of the foregoing description will be briefly described or omitted. 
         [0103]      FIGS. 9 to 11  are views for describing a method fabricating for the optical film  3  according to the third embodiment.  FIG. 12  is a flowchart showing a method fabricating for the optical film  3 . 
         [0104]    Referring to  FIG. 9 , the base film  10  is provided (S 101  of  FIG. 12 ). The matrix layer  20  is formed on the base film  10  (S 102  of  FIG. 12 ). 
         [0105]    The material and size of the base film  10  is selected and provided according to the kind of a light source to which the optical film  3  is applied. 
         [0106]    The matrix layer  20  is formed on the base film  10 . 
         [0107]    For example, the matrix layer  20  is formed, for example, by forming a liquefied matrix resin formed through the mixture and agitation of a silicone resin and a fluorescent material, etc., and then by applying the liquefied matrix resin on the base film  10 . 
         [0108]    The matrix layer  20  is formed, for example, by applying and curing the liquefied matrix resin on the base film  10  through use of a screen printing method, a slit coating method and a roll coating method, etc. The matrix layer  20  is dried and cured at a temperature of about 100° C. by using a microwave and an infrared drier, etc., or is cured by adding the curing agent. 
         [0109]    Referring to  FIG. 10 , the viscous layer  30   a  may be formed on the matrix layer  20  (S 103  of  FIG. 12 ). 
         [0110]    The viscous layer  30   a  has an excellent optical transmittance and thermal resistance, and particularly is made of a resin material or/and a silicon material having an excellent viscosity. For example, the viscous layer  30   a  may be formed of a silicone resin, more preferably, a solvent type silicone resin including toluene. 
         [0111]    It is preferable that the viscous layer  30   a  is formed having a thickness of 20 μm to 100 μm. The viscous layer  30   a  having such a thickness functions to absorb heat which is generated by the light source and is transferred to the fluorescent material included in the matrix layer  20 , thus reducing the degradation of the fluorescent material. 
         [0112]    Regarding the viscous layer  30   a  including volatile toluene, after the viscous layer  30   a  is formed in a state of B-stage on the matrix layer  20 , the viscous layer  30   a  can be cured by heating to about 10° C. and drying through the use of a microwave, an infrared drier, etc., instead of a separate curing agent. However, there is no limit to a method of curing the viscous layer  30   a.    
         [0113]    Through the formation of the viscous layer  30   a , the optical film  3  according to the embodiment has a small thickness, an improved optical transmittance and its simplified manufacturing process. 
         [0114]    Referring to  FIG. 11 , the optical film  3  according to the embodiment can be provided by forming the release film  60  on the viscous layer  30   a  (S 104  of  FIG. 12 ). 
         [0115]    The release film  60  is able to prevent the viscous layer  30   a  from being exposed to the outside and losing a viscosity. The optical film  3  is adhered to a light source by removing the release film  60 . 
         [0116]    In the meantime, for the purpose of improving the reliability of the optical film  3 , it is possible to perform a post-treatment process of heating the optical film  3  at a temperature of from 50° C. to 100° C. for one hour to twenty four hours. 
         [0117]      FIG. 13  is a view showing a light emitting device according to the embodiment. 
         [0118]    Referring to  FIG. 13 , the light emitting device includes a light emitting chip  100  and any one of the optical films  1 ,  2  and  3  which have been described in the first to the third embodiments and include at least one sort of a fluorescent material excited by light emitted from the light emitting chip  100 . 
         [0119]    The light emitting chip  100  may include, for example, a light emitting diode (hereinafter, referred to as LED). However, there is no limit to the kind of the light emitting chip  100 . 
         [0120]    The LED may include, for example, red, green, blue or white light emitting diode, each of which emits a red light, a green light, a blue light or a white light respectively. 
         [0121]    In general, the LED is a kind of a semiconductor device generating light in accordance with an energy band gap difference between nitride semiconductor layers. Since the LED generates only light having a predetermined wavelength band according to the energy band gap difference, the LED has a low color rendering index (CRI) and is difficult to be applied to generate high-quality light. 
         [0122]    Therefore, in the embodiment, a high color rendering index (CRI), for example, a color rendering index (CRI) between 85 and 100 may be obtained by transmitting light emitted from the light emitting chip  100  to the optical films  1 ,  2  and  3 . 
         [0123]    In other words, the light transmitting through the optical films  1 ,  2  and  3  excites at least one kind of the fluorescent material included in the optical film  1  and generates an excited light. The excited light may cause the color rendering index (CRI) of the light emitted from the light emitting chip  100  to be improved. 
         [0124]    Meanwhile, the kind and amount of the fluorescent material included in the optical films  1 ,  2  and  3  may be selected based on a color temperature of the light generated by the light emitting chip  100 . 
         [0125]      FIG. 14  is a table showing kinds and amounts of fluorescent materials included in the optical film  1  in accordance with color temperatures of the light emitting chip  100 .  FIGS. 15 to 20  are graphs showing a color rendering index (CRI) change of the light emitting device when the optical film  1  is applied. 
         [0126]    Referring to  FIGS. 14 ,  15  and  16 , when the color temperature of the light emitting chip  100  is 3,000 K, with respect to 100 weight percent of the matrix layer  20 , the optical film  1  may include 30 to 40 weight percent of the red (R) fluorescent material having a dominant wavelength of 650 nm and 30 to 40 weight percent of the green (G) fluorescent material having a dominant wavelength of 515 nm. 
         [0127]    As shown in  FIG. 15 , regarding the light emitted from the light emitting chip  100 , the intensities of the lights at the vicinity of 515 nm and 650 nm are relatively low, and the lights have hereby low color rendering indexes (CRI). Therefore, the optical film  1  includes the red (R) fluorescent material having a dominant wavelength of 650 nm and the green (G) fluorescent material having a dominant wavelength of 515 nm, thereby allowing the light emitting device to have a color rendering index (CRI) of about 92 as shown in  FIG. 16 . 
         [0128]    Referring to  FIGS. 14 ,  17  and  18 , when the color temperature of the light emitting chip  100  is 4,000 K, with respect to 100 weight percent of the matrix layer  20 , the optical film  1  may include 15 to 25 weight percent of the red (R) fluorescent material having a dominant wavelength of 650 nm and 15 to 25 weight percent of the green (G) fluorescent material having a dominant wavelength of 515 nm. 
         [0129]    As shown in  FIG. 17 , regarding the light emitted from the light emitting chip  100 , the intensities of the lights at the vicinity of 515 nm and 650 nm are relatively low, and the lights have hereby low color rendering indexes (CRI). Therefore, the optical film  1  includes the red (R) fluorescent material having a dominant wavelength of 650 nm and the green (G) fluorescent material having a dominant wavelength of 515 nm, thereby allowing the light emitting device to have a color rendering index (CRI) of about 90 as shown in  FIG. 18 . 
         [0130]    Referring to  FIGS. 14 ,  19  and  20 , when the color temperature of the light emitting chip  100  is 5,000 K, with respect to 100 weight percent of the matrix layer  20 , the optical film  1  may include 5 to 15 weight percent of the red (R) fluorescent material having a dominant wavelength of 650 nm and 8 to 18 weight percent of the green (G) fluorescent material having a dominant wavelength of 515 nm. 
         [0131]    As shown in  FIG. 19 , regarding the light emitted from the light emitting chip  100 , the intensities of the lights at the vicinity of 515 nm and 650 nm are relatively low, and the lights have hereby low color rendering indexes (CRI). Therefore, the optical film  1  includes the red (R) fluorescent material having a dominant wavelength of 650 nm and the green (G) fluorescent material having a dominant wavelength of 515 nm, thereby allowing the light emitting device to have a color rendering index (CRI) of about 92 as shown in  FIG. 20 . 
         [0132]    However, the kind and the amount of the fluorescent material can be changed according to the kind and the color temperature of the light emitting chip  100 . There is no limit to the kind and the amount of the fluorescent material. 
         [0133]      FIG. 21  is a view showing a light unit including the light emitting device. 
         [0134]    Referring to  FIG. 21 , the light unit includes the light emitting chip  100 , the optical films  1 ,  2  and  3  including at least one sort of a fluorescent material excited by light emitted from the light emitting chip  100 , and an optical diffuser diffusing the light passing through the optical films  1 ,  2  and  3 . 
         [0135]    Here, the optical diffuser includes a light guide plate  200  allowing the light passing through the optical films  1 ,  2  and  3  to be used as a surface light source, a diffusion sheet  400  being formed on the light guide plate  200  and diffusing the light, and a reflective sheet  300  being formed under the light guide source  200  and reflecting the light to the light emitting surface of the light guide plate  200 . 
         [0136]    As shown, the optical films  1 ,  2  and  3  are formed between the light emitting chip  100  and the light guide plate  200 . Here, the optical films  1 ,  2  and  3  are adhered to the light emitting surface of the light emitting chip  100  or to the light guide plate  200 . The object to which the optical films  1 ,  2  and  3  are adhered is not limited to this. Meanwhile, a method by which the light unit provides light is not limited to an edge method. The light unit is also able to provide light by a top view method. 
         [0137]    Since the light unit includes the light emitting chip  100  and the optical films  1 ,  2  and  3 , the light unit is able to provide light having a high color rendering index (CRI) and a high quality. Moreover, through use of the optical films  1 ,  2  and  3 , it is possible to minimize the number of the light emitting chip  100  required for implementing a high color rendering index (CRI). 
         [0138]    The features, structures and effects and the like described in the embodiments are included in at least one embodiment of the present invention and are not necessarily limited to one embodiment. Furthermore, the features, structures and effects and the like provided in each embodiment can be combined or modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, the contents related to the combination and modification should be construed to be included in the scope of the present invention. 
         [0139]    The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing embodiments is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.