Safety lens

A planar non-imaging optical element for a solar concentrator comprising a plurality of groups of circular and concentrically arranged microstructures around a centre point, which microstructures are arranged to refract light incident normal to the plane of the solar concentrator towards the centre point, wherein:

• the angle of the microstructures with respect to the plane of the optical element within each group increases with increasing radial distance from the centre point;
• the angles of the microstructures with respect to the plane of the optical element of each of the individual groups are selected such as to form a focal area common to all of the groups at a focal plane of the optical element, when illuminated by light incident normal to the plane of the optical element;
• and
• the angles of the microstructures with respect to the plane of the optical element of each of the individual groups are selected such that, when illuminated by light incident normal to the plane of the optical element, the light refracted from the smallest radial distance from the centre point within a given group and the light refracted from the largest radial distance from the centre point within a given group cross at a plane closer to the optical element than is the focal plane.