Sentence:  On it's trial as a <WSD>sea-light</WSD> at Havre the result was unsatisfactory, as the compromise of merging two different curves in the design halved the concentration of light obtainable from a complete parabolic reflector without gaining sufficient compensation from the wider spread of weak light from the elliptic portion. 
Meaning of the word marked with <WSD> tags:  A light on the seacoast to warn or guide boats.