The searchlight consisted of an electric carbon lamp, capable of a strong beam for target illumination.
Because the bulb was vulnerable to enemy fire, it was protected in a recessed emplacement whilst a large mirror, attached to the end of a 'see-saw' pivoting iron beam reflected the beam across the water to the target.
The light was powered by steam engines usually housed in the nearby forts.
[1] Only a few of these were built anywhere in the British Empire, and were difficult to operate and were never successful.
[2][3] No complete examples have survived but concrete emplacements can still be found at: