Baily Optic

The Baily Optic

This working Optic is the light from Baily lighthouse in Howth, North Dublin. It was installed in 1902 and removed in 1972 when the lighthouse was modernised. The lighthouse was originally gas, then vapourised paraffin powered, the light was equivalent to 2,000,000 candle power. The optic now shines a lesser light over the museum.

Bailey Optic Light, donated by Irish Lights. The lens is a first order annular with a focal distance of 920mm. Its two faces ; one set at 180º, thus giving two flashes every revolution. It floats on a trough of mercury, supported on cast-iron pedestal. The centre bull’s eye and fifteen concentric prisms form the dioptre or refracting part, while the outer prisms form the catadioptic or reflective part of the lens. This lens replaced a non-reflecting lens which had been fitted in 1865 and was itself replaced by an entirely electric light in 1972. This lens, pedestal and weight driven clockwork rotation machine went into operation 1st January 1902, giving a single flash every min. The light source from 1902 to 1908 was a 19 mantle coal gas burner mounted on a lamp changing apparatus with a stand-by six wick oil burner. The coal gas was replaced in 1908 by vaporised paraffin, using a burner with 3 x 50mm mantles. In 1946 a triple 50mm regenerative burner increased the candle power to 2,000,000 from 950,000 candelas.

For an interactive view of the lighthouse (on the Irish Lights site) click here