Optical element, lighting apparatus and solar cell device

An optical element comprising:

• a continuous gradient index distribution area which is configured to continuously attenuate gradient index from a center of the optical element in a radial direction;
• and
• a first medium at the center, the first medium including an area where absolute value of an imaginary part of a complex refractive index of the area is greater than the continuous gradient index distribution area outside the first medium, and the area absorbing light,
• when a refractive index of the continuous gradient index distribution area is N, a radius from the center is r>0, a maximum value of the radius r is r0, a refractive index of an environment outside an outer peripheral surface of the optical element is NO which is a constant, and m is a constant of 1 or more,
• N
• =
• N
• 0
• (
• r
• 0
• r
• )
• m
• is fulfilled.