Patent ID: 7364339

Claim:
A flexible backlight unit for a key of an input device, the unit comprising: a light guide plate formed of flexible transparent resin and having a light guide pattern portion in which a plurality of engraved patterns are formed in a plurality of island shapes, the engraved patterns having a depth on a predetermined regular basis so that light can be diffused and scattered at uniform luminance from each necessary light emitting portion of a rear of the key; and at least one light emitting unit installed at a side wall of the light guide plate, wherein an engraved pattern depth (D) necessary foe the light guide pattern portions is defined as in Equation below: D =A·T·L· 1/[EXP(−4.4·θ 2 )]· S 0 /( S 0 −S p ) where, D: Depth of the engraved pattern (μm), A: Constant value, T: Thickness of the light guide plate (mm), L: Distance from the light emitting unit (mm), θ: Angle between an extension line of central line of the light emitting unit and an imaginary line connecting from the light emitting unit to the light guide pattern portion (radian value: 0 to π/2), S 0 : Space area between a center of the light emitting unit and imaginary lines connecting from the light emitting unit to the light guide pattern portion (mm 2 ), S p : Areas of other light guide pattern portions provided within space between the center line of the light emitting unit and the two imaginary lines connecting from the light emitting unit to the light guide pattern portion (mm 2 ).