please refer to fig1 and fig2 . fig1 is a schematic diagram illustrating a lighting device 1 of a preferred embodiment according to the invention . fig2 is a sectional view of the lighting device 1 in fig1 along the line x - x . the lighting device 1 includes an insulation carrier 12 , a first light source 14 , and a second light source 16 . the insulation carrier 12 has a package space 122 and a light - out side 124 . the light - out side 124 thereon defines a first light - out area 124 a and a second light - out area 124 b ( shown by hatched lines in fig1 ). the insulation carrier 12 includes a positioning groove structure 126 for a reflection sheet 2 ( shown by dashed lines in fig2 ) to be positioned thereon such that the reflection sheet 2 divides the light - out side 124 into the first light - out area 124 a and the second light - out area 124 b . the first light source 14 is disposed in the package space 122 corresponding to the first light - out area 124 a . the second light source 16 is disposed in the package space 122 corresponding to the second light - out area 124 b . thereby , light emitted from the first light source 14 emitting through the first light - out area 124 a out of the lighting device 1 ; light emitted from the second light source 16 emitting through the second light - out area 124 b out of the lighting device 1 . therein , bold lines with arrow show the primary light paths . in other words , in logic , the light passing through the two side of the reflection sheet 2 comes mainly from the first light source 14 and the second light source 16 respectively . therefore , in practice , the light - out quantity by the lighting device 1 for each side of the reflection sheet 2 depends on the light - out quantity of either the first light source 14 or the second light source 16 correspondingly . it is added that , in practice , light emitted by the first light source 14 travels in a plurality of directions , so it is possible that a very few portion of the light may emit through the second light - out area 124 b out of the lighting device 1 . however , the light - out quantity of the portion of the light is obviously much less than the light - out quantity of the light emitting through the first light - out area 124 a out of the lighting device 1 , so the light - out quantity of the portion of the light can be regarded as being with an allowable tolerance so as to be ignored in practice . furthermore , if the first light source 14 is designed properly in structure for convergence of the divergence angle of the first light source 14 , the extent of the light from the first light source 14 emitting through the second light - out area 124 b out of the lighting device 1 can be reduced effectively . the above explanation is also applicable to the second light source 16 , which will be not repeated . in the embodiment , the insulation carrier 12 includes an insulation cup 128 , a lead frame 130 embedded in the insulation cup 128 , and a sealing gel 132 accommodated in the package space 122 . the positioning groove structure 126 is formed on the cup rim of the insulation cup 128 . the first light source 14 and the second light source 16 are disposed on the lead frame 130 . the sealing gel 132 covers the first light source 14 and the second light source 16 . therein , the lead frame 130 can include electrode frames and a heat - conduction structure required for the first light source 14 and the second light source 16 . in practice , the positioning groove structure 126 is formed for example by cutting , after the first light source 14 and the second light source 16 are packaged by the sealing gel 132 , but the invention is not limited thereto . for example , the insulation cup 128 with the positioning groove structure 126 is directly formed by injection . furthermore , in the embodiment , the positioning groove structure 126 includes two indentations disposed oppositely on the cup rim of the insulation cup 128 . the bottom of the indentation is coplanar with the top surface of the sealing gel 132 . but the invention is not limited thereto . for example , in a manufacturing design of forming the positioning groove structure 126 by a secondary working , the positioning groove structure 126 can be formed also on the sealing gel 132 , as shown by fig3 . in this case , the reflection sheet 2 can further extend into the sealing gel 132 for separating the light emitted by the first light source 14 and the second light source 16 more effectively . please also refer to fig4 . fig4 is a top view of the lighting device 1 ; therein , the positions of the first light source 14 and the second light source 16 are indicated by dashed lines , and the first light - out area 124 a and the second light - out area 124 b are still shown by hatched lines . in the embodiment , the lighting device 1 shows a rectangular solid appearance ; that is , the insulation cup 128 has a rectangular profile at the light - out side 124 . the first light source 14 and the second light source 16 are disposed in a short side direction of the rectangular profile . in practice , each of the first light source 14 and the second light source 16 includes at least one light - emitting diode chip , but the invention is not limited thereto . in a common case , the first light source 14 and the second light source 16 usually use light - emitting diode chips in same size and light - emitting efficiency , so for simple illustration in the description , the ratio of the light - out quantity of the light - emitting diode chips of the first light source 14 to that of the second light source 16 is directly indicated by the ratio of the size of the rectangle by dashed lines for the first light source 14 to that for the second light source 16 . in other words , the above ratio also indicates the ratio of the light - emitting power of the first light source 14 to that of the second light source 16 , as well as the ratio of the light - out quantity of the first light source 14 to that of the second light source 16 . in the embodiment , the first light source 14 is equivalent to the second light source 16 . please refer to fig5 , which is a top view of a lighting device according to another embodiment . the lighting device 3 is substantially identical in structure to the lighting device 1 . except for the difference , the lighting device 3 still uses the same denomination as the lighting device 1 . the main difference between the lighting device 3 and the lighting device 1 is the disposition of the first light source 34 and the second light source 36 of the lighting device 3 . as shown by fig5 , the light - emitting power of the first light source 34 is larger than the light - emitting power of the second light source 36 , so the light - out quantity from the first light - out area 324 a is larger than the light - out quantity from the second light - out area 324 b . it is added that if the first light source 34 and the second light source 36 are disposed in the same disposition of light - emitting diode chips ( for example , in disposition density ), the light - emitting power of the first light source 34 and the second light source 36 can be reflected by the sizes of the areas of the first light - out area 324 a and the second light - out area 324 b respectively . for example , in the embodiment , the area of the first light - out area 324 a corresponding to the first light source is larger than the area of the second light - out area 324 b corresponding to the second light source 36 . for other description about the lighting device 3 , please refer to the relevant description of the lighting device 1 . it will not be repeated . please refer to fig6 , which is a top view of a lighting device according to another embodiment . the lighting device 4 is substantially identical in structure to the lighting device 1 . except for the difference , the lighting device 4 still uses the same denomination as the lighting device 1 . the main difference between the lighting device 4 and the lighting device 1 is the disposition of the first light source 44 and the second light source 46 of the lighting device 4 . as shown by fig6 , the first light source 44 and the second light source 46 are disposed in a long side direction of the rectangular profile . the light - emitting power of the first light source 44 is larger than the light - emitting power of the second light source 46 , so the light - out quantity from the first light - out area 424 a is larger than the light - out quantity from the second light - out area 424 b . for other description about the lighting device 4 , please refer to the relevant description of the lighting devices 1 and 3 . it will not be repeated . it is added that , in the above embodiments , the lighting devices 1 , 3 and 4 are illustrated to be with a top - view rectangular profile , but the invention is not limited thereto . for example , a top - view square profile , a top - view circular profile , and other top - view profiles are applicable to the invention , which will not be repeated . please refer to fig7 , which is a sectional view of a back light module 5 , which has a lighting device of the invention , of a preferred embodiment according to the invention . therein , for simple illustration , the components are shown by magnifying . the back light module 5 includes a frame 52 , a light - guiding structure 54 , and a first lighting device 56 and a second lighting device 58 disposed at two sides of the light - guiding structure 54 . for simple explanation , the embodiment uses the abovementioned lighting device 1 as the first lighting device 56 and the second lighting device 58 . thus , the denomination for the first lighting device 56 and the second lighting device 58 directly follows the denomination of the lighting device 1 , and the relevant description of the lighting device 1 is also applicable herein and is not repeated herein . the light - guiding structure 54 includes a first light - guiding part 542 , a second light - guiding part 544 disposed opposite to the first light - guiding part 542 , and a reflection sheet 546 disposed between the first light - guiding part 542 and the second light - guiding part 544 . the light - guiding structure 54 has a first light - in side 54 a and a second light - in side 54 b opposite to each other . the first lighting device 56 is disposed close to the first light - in side 54 a . a first edge 546 a of the reflection sheet 546 contacts the positioning groove structure 126 of the first lighting device 56 to divide the light - out side 124 into the first light - out area 124 a and the second light - out area 124 b of the first lighting device 56 , such that the first light - out area 124 a and the second light - out area 124 b are opposite to the first light - guiding part 542 and the second light - guiding part 544 respectively . therefore , light emitted by the first light source 14 emitting through the first light - out area 124 a out of the first lighting device 56 to enter the first light - guiding part 542 through the first light - in side 54 a ; light emitted by the second light source 16 emitting through the second light - out area 124 b out of the second lighting device 58 to enter the second light - guiding part 544 through the second light - in side 54 b . similarly , the second lighting device 58 is disposed opposite to the first lighting device 56 and close to the second light - in side 54 b , such that a second edge 546 b of the reflection sheet 546 contacts the positioning groove structure 126 of the second lighting device 58 to divide the light - out side 124 into the first light - out area 124 a and the second light - out area 124 b of the second lighting device 58 . other detailed disposition of the second lighting device 58 is the same as the first lighting device 56 , which will not be repeated . in the embodiment , the back light module 5 is applied to a bi - directional display apparatus , so in fig7 , each of the first light - guiding part 542 and the second light - guiding part 544 thereon disposes a liquid crystal panel 72 and 74 . each of the first light - guiding part 542 and the second light - guiding part 544 is a light - guiding plate for providing required back light to the liquid crystal panels 72 and 74 correspondingly . the first light - guiding part 542 , the second light - guiding part 544 , and the reflection sheet 546 are stacked in a sandwich structure . it is added that , in practice , the back light module 5 includes a plurality of the lighting devices 56 and 58 at the first light - in side 54 a and the second light - in side 54 b respectively . each group of the lighting devices 56 and the lighting devices 58 is arranged and soldered in a row on a circuit board 60 and 62 to form a bar light source module . furthermore , in the above embodiment , the back light module 5 uses the first lighting device 56 and the second lighting device 58 disposed opposite to each other ; that is , the first light - in side 54 a is opposite to the second light - in side 54 b . the light - out uniformity of the first light - guiding part 542 and the second light - guiding part 544 is therefore improved . however , the invention is not limited thereto . for example , if the intensity of the back light provided by the first lighting devices 56 is sufficient , the second lighting devices 58 can be omitted ; in practice , the first light - in side 54 a and the second light - in side 54 b can be disposed to be adjacent ; even lighting devices can be disposed at several sides of the light - guiding structure 54 . in addition , in the embodiment , the back light module 5 includes reflection plates 64 and 66 at the lighting devices 56 and 58 respectively , which provides effect of fixing the lighting devices 56 and 58 and the light - guiding structure 54 and preventing light leakage thereby . the frame 52 can directly support the liquid crystal panels 72 and 74 ; the reflection plates 64 and 66 support the light - guiding structure 54 and the lighting devices 56 and 58 . in the above embodiments , each of the first light - guiding part 542 and the second light - guiding part 544 is a flat plate , but the invention is not limited thereto . please refer to fig8 , which is a sectional view of a back light module 8 according to another embodiment . the back light module 8 is substantially identical in structure to the back light module 5 . except for the difference , the back light module 8 still uses the same denomination as the back light module 5 . the main difference between the back light module 8 and the back light module 5 is that each of the first light - guiding part 842 and the second light - guiding part 844 of the first light - guiding part 842 of the light - guiding structure 84 of the back light module 8 is a wedge light - guiding plate , which is conducive to the light - out uniformity of the first light - guiding part 842 and the second light - guiding part 844 , so the back light module 8 is provided with the lighting device 56 only at one side of the light - guiding structure 84 . in addition , it is added that the lighting device of the invention can provide different light - out quantities ; that is , the back light module provides different the light - out quantities by different light - guiding parts , so the back light intensity provided by the first light - guiding part and the second light - guiding part can be controlled by way of designing the light - out quantities provided by the lighting device through the first light - out area and the second light - out area respectively , so as to be adapted to different requirements of different products . for an example of a foldable mobile phone with dual screens , the outside screen thereof is usually small and used for indication display , so the back light intensity therefor is usually not high and the back light - out quantity is less . for this case , the lighting device 3 in fig5 is applicable . those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention . accordingly , the above disclosure should be construed as limited only by the metes and bounds of the appended claims .