Book 6, Question 104
Why Does a Lighthouse Flash?
A lighthouse is a tall lamp with a fingerprint. Each one flashes its own pattern, like long, short, pause. That pattern tells sailors, this cape, not that one!
From the book
Page from A Million Whys Book 6
More fun facts
- The Bodie Island Lighthouse in North Carolina has a big Fresnel lens whose flash pattern reaches more than 20 miles out to sea.
- A Fresnel lens has hundreds of specially cut pieces of glass around the lamp.
- How many times a light flashes each minute depends on how many flash panels the lens has and how fast it turns.
- One light may flash every five seconds, while another flashes white every 7.5 seconds.
- In one lighthouse lens, 24 bull's-eye shaped lenses made the flashes.
- Lighthouse lenses were first used in England in the 1700s and in the United States by 1810.
- August 7 is National Lighthouse Day.
Sources: National Park Service, National Park Service, National Park Service, National Park Service, NOAA Ocean Service
Questions kids ask
What makes a lighthouse light flash?
A lens with special glass panels turns around the lamp, and each panel sends out a flash as it passes.