Cast your mind back to 2008 and think about what you remember of that year. Perhaps it was the global banking crisis and Gordon Brown’s alleged rescue of international finance. Maybe it was CERN switching on the Large Hadron Collider and then swiftly needing to repair its blown magnets. Or perhaps it was all the talk about high-temperature iron-based superconductors. But whatever your personal recollections, you surely won’t remember that the United Nations (UN) declared 2008 to be the International Year of the Potato.

Now it’s easy to laugh at the idea of celebrating potatoes, which is why I just did, but then the UN has been good for science too. In the decade since the potato was king of the crop, we’ve had international years devoted to astronomy (2009), chemistry (2011), crystallography (2014) and then light (2015). Physics, of course, took centre stage in 2005 to mark the centenary of Einstein’s papers on Brownian motion, the photoelectric effect, special relativity and E = mc².

The International Year of Light was an apparent success, with organizers claiming more than 13,000 activities in almost 150 countries attended by an audience of more than 100 million. You might wonder, therefore, why we need an International Day of Light, the first of which is to be celebrated on Wednesday 16 May. Surely we’ve “done” light?

Not so, according to the organizers, who kick off with a launch event today at the headquarters of the UN Educational, Scientific and Cultural Organization (UNESCO) in Paris. The goals are ambitious: improve the public’s understanding of light; show the link between light and culture; highlight research and careers in light science; and seek ways to curb light pollution. But to me the most worthwhile effort is promoting alternative sources of light for people in developing nations not connected to the electricity grid, many of whom rely on dangerous kerosene lamps for light after dark.

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International Year of Light 2015: our top 10 articles on light now with added videos

My favourite is GravityLight – a lamp attached to a heavy 12 kg bag. Simply lift the bag up to a height of about 2 m with your hands and, as it descends slowly over the course of half an hour to the floor, gravitational energy is converted into electrical energy to turn on a light-emitting diode (LED) bulb. It’s a beautiful idea with some simple physics principles at its heart.

So my message is – don’t let the International Day of Light pass you by. There are lots of activities and events to get involved in. If nothing else, check out the Physics World website on 16 May for some light-themed treats in our special light-themed collection or read this month’s Focus on Optics and Photonics. It would be a shame if the International Day of Light went the way of the International Year of the Potato, which is to be well and truly forgotten.

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