Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)

A man drinks at a "colored" water cooler in a streetcar terminal in Oklahoma City, July 1939. (Photo by Reuters/Library of Congress)

A woman covers her face as men throw colored powder at her during “Lathmar Holi” at the village of Barsana in the northern Indian state of Uttar Pradesh March 9, 2014. (Photo by Anindito Mukherjee/Reuters)

Pro-Russian activists attack policemen guarding the burned trade union building in the southern Ukrainian city of Odessa on May 3, 2014. More than 30 people were killed in a “criminal” blaze in Ukraine's southern city of Odessa, as violence spread across the country during the bloodiest day since Kiev's Western-backed government took power. Ukraine's interior ministry said at least 31 people had died in the fire Friday, with local media reporting that pro-Russian militants were believed to have been in the burning building at the time. (Photo by Anatolii Stepanov/AFP Photo)

A scavenger sifts through garbage piled on the bank of Beirut river, Lebanon August 24, 2015. Lebanese protest organisers called for a fresh demonstration against the government on Saturday after two days of rallies that turned violent in central Beirut and wounded scores of people. The “You Stink” campaign has mobilised against the government's failure to solve a garbage disposal crisis, bringing thousands of people onto the streets in protests that have threatened the survival of the cabinet. (Photo by Mohamed Azakir/Reuters)

A person enter in sauna on the peak of Mount Lagazuoi in Cortina D'Ampezzo, Italy January 16, 2018. Picture taken January 16, 2017. (Photo by Stefano Rellandini/Reuters)

A demonstrator holds a rose and shouts slogans in front of a riot policeman during an unauthorized march called by secondary students to protest against government education reforms in Valparaiso, Chile, May 26, 2016. (Photo by Rodrigo Garrido/Reuters)

Members of the Bearded Ladies Cabaret cross Broad St., before a march by supporters of Sen. Bernie Sanders, I-Vt., in Philadelphia, on the first day of the Democratic National Convention, July 25, 2016. (Photo by Tom Williams/CQ Roll Call/AP Images)