A security element comprising a first and a second pattern formed in or on a substrate, the first pattern (105;205) being formed by discrete elements (105a-105g;205a-205c) of a first material that are distributed over a first region of the substrate (100;200), the second pattern (106;206) being formed by discrete elements (106a-106i;206a-206c) of a second material that are distributed over a second region of the substrate (100;200), said second material being different from said first material, said first and second regions of the substrate overlapping, the discrete elements of at least one of the first and second patterns are distributed randomly, a part of the discrete elements of the first pattern (105;205) overlap with a part of the discrete elements of said second pattern (106;206), the security element is defined by the first pattern (105;205), the second pattern (106;206) and a third pattern (107;207) formed by the overlap of some or all of the discrete elements of said first and second patterns, and the first material comprises a first fluorescent dye or pigment, which upon excitation by electromagnetic radiation falling within an excitation wavelength range λ1a of the first fluorescent dye or pigment is capable of emitting electromagnetic radiation in at least one first emission wavelength range λ1e, wherein the second material comprises a second fluorescent dye or pigment, which upon excitation by electromagnetic radiation falling within an excitation wavelength range λ2a of the second fluorescent dye or pigment is capable of emitting electromagnetic radiation in at least one second emission wavelength range λ2e, and wherein said first emission wavelength range λ1e of the first fluorescent dye or pigment overlaps with the excitation wavelength range λ2a of the second fluorescent dye or pigment, so that upon irradiation with electromagnetic radiation within the excitation wavelength range λ1a of the first fluorescent dye or pigment the second fluorescent dye or pigment is excited, in the area of overlap of the discrete elements, to emit electromagnetic radiation in the emission wavelength range λ2e, wherein said first and second patterns are formed such that said part of the discrete elements of the second pattern (106;206) which overlap with said part of the discrete elements of the first pattern (105;205) are formed over said part of the discrete elements of the first pattern (105;205), or said part of the discrete elements of the first pattern (105;205) which overlap with said part of the discrete elements of the second pattern (106;206) are formed over said part of the discrete elements of the second pattern (106;206) provided that the first material is substantially translucent or transparent to electromagnetic radiation in the second emission wavelength range λ2e. said part of the discrete elements of the second pattern (106;206) which overlap with said part of the discrete elements of the first pattern (105;205) are formed over said part of the discrete elements of the first pattern (105;205), or said part of the discrete elements of the first pattern (105;205) which overlap with said part of the discrete elements of the second pattern (106;206) are formed over said part of the discrete elements of the second pattern (106;206) provided that the first material is substantially translucent or transparent to electromagnetic radiation in the second emission wavelength range λ2e.