The Electric Light appears to have been of the Reflecting Type. The Light itself being underground and protected by concrete. The Light was aimed at a reflector above ground.
From: Illumination of Fortified Harbours (1889)
..... and when we consider the great cost of these lights, their extreme vulnerability to machine and other fire, and the inconvenience to the defence flotilla which their injudicious use may often occasion, it would appear desirable to limit the electric lights to a moderate number at each harbour. Some experts consider that there cannot be too many of them. This is probably a mistake. As before stated, such a light should act direct from its lantern when used for searching purposes ; but when a hostile flotilla comes to close quarters, these expensive lanterns should be lowered under cover and an arrangement raised whereby the ray of light can be reflected in any desired direction by a cheap plane mirror that can be readily replaced when broken.
There is a certain loss of light when a mirror is used. The quantity of light reflected from polished metal surfaces is greatest when the angle of incidence (between the ray of light and the normal to the surface) is small, but an exactly opposite result is obtained with non metallic surfaces, such as water, glass, &c.
The first emplacement is marked on 1896 plans as being a “Temporary Emplacement for Electric Light”.
By 1910 as part of the upgrading of the fort, two new 3° Electric Light Emplacements had been constructed. One at Siloso Point, reached by a stairway, and the other on the cliff at the east of the Fort. This was reached by a path and a sloping path and a stairway. These lights were direct beam, not reflected. These were designed to illuminate targets for the 6 Inch QF Guns.
The first Electric Light is also indicated in handwriting as being a D.E.L. on an October 1910 plan, shown left. But the emplacement itself is not shown. Another plan dated only a month later does not show it at all. Both of the new Electric Lights appear on both plans.
The two Lights gave the fort a much needed night fighting capability. The 6 Inch QF Guns out-ranged the Mark IV 9·2 Inch Gun and had a significantly improved rate of fire, making them more suitable for night action.
I am indebted to Leslie Lauw for locating the remains of the first Electric Light, and for the use of his photos. Leslie has a blog entitled, ‘Amazing Walks’. It’s well worth a visit.