From Live Design:
Niagara Falls was first lit in 1860 with 200 Bengal lights for a celebration for the Prince of Wales. The first use of electric lights came in 1879, when the falls were illuminated by carbon arc lights for a special visit by the governor-general of Canada. Then 1901 saw the falls lit for an entire week during the Pan-American Exposition and, subsequently, in 1907 for a month-long display. Searchlights aimed at the American falls were colored by gelatin film placed in front of the lights by men that were paid 50¢ per night to stand beside them, changing colors by listening for a commanding series of whistle blows.
Read the rest of the article to learn more about the history of the lights.