a substrate and a plurality of LED light sources disposed on the substrate following a grid pattern to form a plurality of rectangle-shaped lighting units,

wherein each lighting unit comprises four LED light sources disposed at the lighting unit's four corners, respectively, has a length L along a first direction X and a width W along a second direction Y, and irradiates a corresponding rectangular area with the same length L and width W on an interface of the display device, wherein any two adjacent ones of the plurality of rectangle-shaped lighting units share at least one of the plurality of LED light sources,

wherein each LED light source comprises an LED and a corresponding lens disposed above the LED, the corresponding lens directing light rays emitted from the LED onto

(1) a first corner of the corresponding rectangular area on the interface of the display device with a first luminance value E1,

(2) a second corner of the corresponding rectangular area with luminance of zero or substantially close to zero, wherein a distance between the first corner and the second corner is L along the first direction X,

(3) a first location (x, 0) with a luminance value E (x, 0) that is determined based on a linear change of luminance value from the first luminance value E1 at a first spot to a luminance value substantially close to zero at a second spot, wherein the first location, the first spot, and the second spot are on a first border line between the first corner and the second corner, and x is a distance between the first location (x, 0) and the first corner along the first direction X,

(4) a third corner of the corresponding rectangular area with luminance of zero or substantially close to zero, wherein a distance between the first corner and the third corner is W along the second direction Y,

(5) a second location (0, y) with a luminance value E (0, y) that is determined based on a linear change of luminance value from the first luminance value E1 at a third spot to a luminance value substantially close to zero at a fourth spot, wherein the second location, the third spot, and the fourth spot are on a second border line between the first corner and the third corner, and y is a distance between the second location (0, y) and the first corner along the second direction Y, and

(6) a third location (x, y) of the corresponding rectangular area with a luminance value of E (x, y) that is a product of E (x, 0) and E (0, y).