5 Euros International Year of Light

The United Nations designated 2015 as the International Year of Light to mark several scientific anniversaries converging in that year — among them the 1,000th anniversary of Ibn al-Haytham's Book of Optics and the 150th anniversary of Maxwell's equations describing electromagnetic radiation. San Marino, as a non-EU microstate that retains its own euro-denominated coinage rights through bilateral agreement with Italy, routinely issues commemorative silver pieces for UN-designated years, keeping mintages low enough to sustain collector demand without flooding the market.