reference will now be made in detail to the embodiments of the present disclosure , examples of which are illustrated in the accompanying drawings , wherein like reference numerals refer to like elements throughout . fig1 is a perspective view illustrating the exterior of a washing machine according to an embodiment of the present disclosure . as illustrated in fig1 , the washing machine includes a main body 10 that constitutes the exterior , a tub ( not shown ) which is installed in the main body 10 and in which washing water is stored , and a drum 12 that is rotatably disposed in the tub so as to wash laundry . a laundry port 13 through which laundry may be put into the drum 12 , is formed at a front side of the main body 10 , and a door 14 is installed to open / close the laundry port 13 . a control panel assembly 100 is disposed at an upper part of the front side of the main body 10 so that a user may control an operation of the washing machine . fig2 is an exploded perspective view illustrating a structure of the control panel assembly 100 of the washing machine illustrated in fig1 , according to an embodiment of the present disclosure , fig3 is a cross - sectional view illustrating a combined state of the control panel assembly 100 illustrated in fig2 , fig4 is an enlarged cross - sectional view of a portion a of fig3 , fig5 is a cross - sectional view of a light emitting diode ( led ) bracket , and fig6 is an enlarged view of a portion b of fig5 . as illustrated in fig2 through 6 , the control panel assembly 100 includes a control panel 110 having one side in which an opening 111 is formed and a circuit board 120 mounted at an inner side of the control panel 110 . a rotary switch 121 is installed at the circuit board 120 , and a plurality of leds 122 are installed on the periphery of the rotary switch 121 . the rotary switch 121 includes a push shaft 121 a that protrudes forward and a rotation shaft 121 b that surrounds a lower side of the push shaft 121 a . a rotary knob 160 is combined with the rotary switch 121 . the user may rotate the rotation shaft 121 b of the rotary switch 121 via the rotary knob 160 or may press the push shaft 121 a to select various operations of the washing machine , such as a washing course , a washing time , and the like . also , an led bracket 130 is installed at the circuit board 120 . the led bracket 130 includes a light guide part 131 that accommodates and protects the plurality of leds 122 and simultaneously guides light emitted from the leds 122 toward the front of the control panel 110 . a first through hole 132 through which the rotation shaft 121 b and the push shaft 121 a of the rotary switch 121 pass , is formed in the center of the led bracket 130 . the light guide part 131 includes a plurality of light guide holes 131 a that are formed on the periphery of the first through hole 132 and are spaced apart from each other by a predetermined gap in a circumferential direction of the led bracket 130 . as shown in fig3 , the plurality of light guide holes 131 a include first light guide holes 133 in which the leds 122 are accommodated and second light guide holes 134 formed to have a step height with respect to the first light guide holes 133 . the first light guide holes 133 and the second light guide holes 134 may be formed in an approximately rectangular form so as to prevent light emitted from the leds 122 from being diffused . that is , the first light guide holes 133 and the second light guide holes 134 are provided in the rectangular form . thus , when light emitted from the leds 122 passes through the light guide holes 131 a , the light is guided toward one light transmission protrusion 142 a disposed in a position corresponding to the light guide holes 131 a on a path of light emitted from the leds 122 and proceeds , thereby preventing light from being diffused to other light transmission protrusions that do not correspond to the light guide holes 131 a . furthermore , since the second light guide holes 134 are formed to have a step height with respect to the first light guide holes 133 and the cross - sectional area of each second light guide hole 134 is smaller than that of each first light guide hole 133 , there is the effect of focusing light emitted from the leds 122 . the cross - sectional area of the first light guide hole 133 may be gradually decreased and the cross - sectional area of the second light guide hole 134 may be gradually increased along the proceeding path of light emitted from the leds 122 , so as to easily remove a mold for forming the first light guide holes 133 and the second light guide holes 134 when the led bracket 130 is injection molded using plastic . the shape of the first light guide holes 133 and the second light guide holes 134 is not limited to the rectangular shape and may be all polygonal shapes in which diffusion of light emitted from the leds 122 may be prevented . also , each second light guide hole 134 may be relatively longer than each first light guide hole 133 , so as to allow light emitted from the leds 122 to be further focused when light emitted from the leds 122 proceeds forward along the second light guide holes 134 . the degree to which light emitted from the leds 122 is focused may be determined by a ratio ( l2 / l1 ) of a length l2 of the second light guide hole 134 to a length l1 of the first light guide hole 133 . the ratio ( l2 / l1 ) of the length l2 of the second light guide hole 134 to the length l1 of the first light guide hole 133 may be approximately equal to or greater than 1 . 5 and equal to or less than 5 . the reason why the ratio ( l2 / l1 ) of the length l2 of the second light guide hole 134 to the length l1 of the first light guide hole 133 has a predetermined range is that , as the length l2 of the second light guide hole 134 increases , the effect of focusing light emitted from the leds 122 increases but the thickness of the led bracket 130 in which the second light guide holes 134 are formed increases . of course , the ratio ( l2 / l1 ) of the length l2 of the second light guide hole 134 to the length l1 of the first light guide hole 133 is not limited to being equal to or greater than 1 . 5 and equal to or less than 5 and may be equal to or less than 1 . 5 or equal to or greater than 5 according to design specifications . in this way , the cross - sectional areas or lengths of the light guide holes 131 a may be properly adjusted so that light emitted from the leds 122 may reach a desired position with a desired degree of focusing . an led window 140 and a knob guide 150 are installed at the opening 111 of the control panel 110 , and the rotary knob 160 is combined with the front of a knob guide 150 . the knob guide 150 supports the rotary knob 160 and prevents movement of the rotary knob 160 . the led window 140 serves to display a function selected through a rotation or pressing operation of the rotary knob 160 , so that the user may identify the function . the led window 140 includes a ring - shaped base plate 141 coupled to a rear side of the knob guide 150 , a light transmission part 142 formed in a circumferential direction of the ring - shaped base plate 141 , and a light diffusion part 143 formed at a rear side of the base plate 141 corresponding to the front side of the led bracket 130 . the light transmission part 142 includes a plurality of light transmission protrusions 142 a that are spaced apart from each other by a predetermined gap in the circumferential direction of the ring - shaped base plate 141 and protrude from the front side of the base plate 141 so that light passing through the light guide holes 131 a of the led bracket 130 may be transmitted to the front of the control panel 110 . the light diffusion part 143 is configured in many uneven forms formed in units of approximately several micrometers to several hundreds of micrometers at the rear side of the base plate 141 . the uneven forms may be formed by performing corrosion treatment on the rear side of the base plate 141 or by mechanical processing and may be pre - formed on a mold for injection - molding the led window 140 . also , instead of forming protrusions in the uneven forms at the rear side of the base plate 141 , the light diffusion part 143 may be provided by attaching a thin material , such as a film , of which surface treatment for diffusing light is performed , to the front side or rear side of the base plate 141 of the led window 140 or by inserting the thin material , such as the film , when the led window 140 is injection molded . the light diffusion part 143 allows light emitted from the leds 122 and passing through the led bracket 130 to be uniformly diffused into one light transmission protrusion 142 a and to be transmitted by the light transmission protrusions 142 a , thereby generating the effect of appealing lighting . the led bracket 130 and the led window 140 may be formed integrally with each other using a manufacturing method , such as injection molding . in this case , since it is not easy to additionally form uneven protrusions at the rear side of the base plate 141 , the thin material , such as the film , of which surface treatment for diffusing light is performed , may be inserted when the led bracket 130 and the led window 140 are integrally injection molded . the knob guide 150 includes a base panel 151 on which the rotary knob 160 is mounted , hanging jaws 152 that protrude from a circumference of the base panel 151 , and a plurality of second through holes 153 that are spaced apart from each other by a predetermined gap in the circumferential direction of the base panel 151 . a character or symbol is printed on the circumference of the base panel 151 so that the user may identify an operation selected by the rotary knob 160 . the hanging jaws 152 are hung on the periphery of the opening 111 when the knob guide 150 is installed at the control panel 110 . the plurality of second through holes 153 are formed through the base panel 151 in a position corresponding to the light transmission protrusions 142 a so that the plurality of light transmission protrusions 142 a may be inserted into the plurality of second through holes 153 and may be exposed to the front side of the control panel 110 . also , the knob guide 150 includes a boss insertion part 154 that protrudes from the center of the knob guide 150 and at least one first hook 155 disposed on a circumference of the boss insertion part 154 . the boss insertion part 154 includes a boss insertion hole 154 a through which a boss 161 of the rotary knob 160 may be inserted into the boss insertion part 154 . the boss insertion part 154 confines the boss 161 of the rotary knob 160 so as to prevent movement of the rotary knob 160 . the first hook 155 allows a second hook 162 of the rotary knob 160 to be engaged with the first hook 155 so that the rotary knob 160 may be rotatably mounted on the knob guide 150 . also , the first hook 155 prevents the rotary knob 160 from being deviated when the user pulls the rotary knob 160 . the rotary knob 160 includes a boss 161 that extends from an inner side of the rotary knob 160 toward the center of the knob guide 150 to a predetermined length , and at least one second hook 162 disposed on a circumference of the boss 161 . the boss 161 is inserted into the boss insertion part 154 when the rotary knob 160 is mounted on the knob guide 150 , and a shaft insertion hole 161 a is formed in the boss 161 so that the push shaft 121 a of the rotary switch 121 may be inserted into the shaft insertion hole 161 a . as described above , the second hook 162 is coupled to the first hook 155 so that the rotary knob 160 may be rotatably mounted on the knob guide 150 . in fig2 , three first hooks 155 and three second hooks 162 are disposed in the circumferential direction of the knob guide 150 and in the circumferential direction of the rotary knob 160 , respectively . however , the number of first hooks 155 and second hooks 162 may be changed according to design requirements . also , in fig3 , the first hook 155 and the second hook 162 are engaged with each other so that the rotary knob 160 may be coupled to the knob guide 150 . however , a hook may be formed at either of the rotary knob 160 and the knob guide 150 , and a coupling hole to be coupled to the hook is formed at the other one of the rotary knob 160 and the knob guide 150 so that the rotary knob 160 and the knob guide 150 may be coupled to each other . hereinafter , an operation of assembling the control panel assembly 100 of the washing machine according to the present disclosure will be described . fig7 a through 7c illustrate an operation of assembling the control panel assembly 100 of fig2 of the washing machine of fig1 , according to an embodiment of the present disclosure . first , as illustrated in fig7 a , when the knob guide 150 is inserted into the opening 111 of the control panel 110 at the rear of the control panel 110 in a state in which the led window 140 is coupled to the knob guide 150 , the base panel 151 and the light transmission part 142 are exposed to the front of the control panel 110 through the opening 111 . the led bracket 130 is combined with the circuit board 120 so as to accommodate and protect the rotary switch 121 and the leds 122 installed at the circuit board 120 . in this case , the push shaft 121 a and the rotation shaft 121 b of the rotary switch 121 protrude forward through the first through hole 132 . next , as illustrated in fig7 b , the circuit board 120 is fixed to the control panel 110 on which the knob guide 150 is installed , using a fastening member , such as a screw . then , the push shaft 121 a and the rotation shaft 121 b of the rotary switch 121 are exposed to the front of the control panel 110 via the boss insertion part 154 of the knob guide 150 . subsequently , as illustrated in fig7 c , the rotary knob 160 is combined with the knob guide 150 at the front of the control panel 110 . in this case , the boss 161 of the rotary knob 160 is inserted into the boss insertion part 154 , and the second hook 162 of the rotary knob 160 is engaged with the first hook 155 of the knob guide 150 . when the boss 161 of the rotary knob 160 is inserted into the boss insertion part 154 , the push shaft 121 a of the rotary switch 121 is inserted into the shaft insertion hole 161 a formed in the boss 161 and is coupled to the boss 161 . it is apparent that the above - described control panel assembly 100 may be applied to not only a washing machine but also all electronic products that require operation control with user manipulation , such as a drying machine , a dishwasher , and the like . as described above , according to the embodiments of the present disclosure , since light emitted from a plurality of leds is uniformly diffused , the effect of appealing lighting can be achieved and good impression can be given to the user so that the reliability of a product can be improved . in addition , no additional component , such as a film , is required so that the productivity of the product can be improved . although a few embodiments of the present disclosure have been shown and described , it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention , the scope of which is defined in the claims and their equivalents .