Passage: Real estate developers Woodruff and Shoults called their development "Hollywoodland" and advertised it as a "superb environment without excessive cost on the Hollywood side of the hills."They contracted the Crescent Sign Company to erect thirteen south-facing letters on the hillside. The sign company owner, Thomas Fisk Goff (1890–1984), designed the sign. Each letter was 30 feet (9.1 m) wide and 50 feet (15.2 m) high, and the whole sign was studded with around 4,000 light bulbs. The sign flashed in segments: "HOLLY," "WOOD," and "LAND" lit up individually, and then the whole. Below the Hollywoodland sign was a searchlight to attract more attention. The poles that supported the sign were hauled to the site by mules. Cost of the project was $21,000, equivalent to $310,000 in 2018.

Question: How many light bulbs was studded on the whole sign?
4,000