Patent ID: 8567979

Claim:
A light emitting diode (LED) lens of a direct type back light module, a dispersion index of said LED lens is less than 0.1; said dispersion index is: k dispersion = ∫ A ⁢ ∑ i ⁢ ⁢ d i d total ⁢ ⁢ ⅆ A ; wherein: dA is a microfacet of the main luminous surface of an LED blue chip; di is a solid angle of the incident angle which is just in the critical area when dA light is reflected to the lens; said critical area refers to an area in which light with different wavelengths emitted by the LED is dispersed in the lens; the total solid angle of color separation corresponding to microfacet dA is: ∑ i ⁢ ⁢ d i ; and d total is a solid angle of the light emergent surface of the lens corresponding to any microfacet dA.