International Day of Light
The International Day of Light is celebrated each year on May 16. Its purpose, per UNESCO, is to strengthen cooperation and leverage its potential to foster peace and development. Light-based technologies play an important role in education, science, art, culture,  sustainable development, communications, energy and medicine. The annual celebration is organized by UNESCO

History 
The first International Day of Light celebration was organized by UNESCO on May 16, 2018, the anniversary of the day in 1960 when engineer and physicist Theodore Maiman successfully fired the first laser.

The International Day of Light followed the International Year of Light in 2015. The Day was proposed by Ghana, Mexico, New Zealand and the Russian Federation and was supported by UNESCO's Executive Board. The UNESCO General Conference approved the proposal in November 2017.

Purpose 

The study of light, and light-based technologies, has helped us transform our world in extraordinary ways. Light-based technologies include microscopes, X-ray machines, telescopes, cameras, electric lights and television screens.  The International Day of Light is intended to promote scientific cooperation and to harness the potential of science to foster peace and sustainable development.

References 

UNESCO
United Nations days
May observances