Bridges and watchtowers at the Imperial Palace were illuminated when Emperor Akihito turned 79 years old on Sunday as about 1,000 people looked on.
The nocturnal display, the first at the palace for an event other than banquets for state guests, will run for 15 days, the Imperial Household Agency said.
Bystanders cheered when the stone bridge at the Ote-mon Gate, the Fushimi-yagura Keep, Mount Fuji-view Keep and the remains of Edo Castle were lit up at 5 p.m.
The lights are extinguished at 10 p.m.
Yoriko Kato, 68, who came from Yokohama for the event, said: "They're indeed beautiful with the lighting."