Lighthouse In Waves

Prior to modern strobe lights, lenses were used to concentrate the light from a continuous source. Two tasks were involved:
- vertical light rays of the lamp are redirected into a horizontal plane
- horizontally the light is focused into one or a few directions at a time, with the light beam sweeping around; as a result, in addition to seeing the side of the light beam, one can see the light directly from a further distance away.