Although the metallic parabolic reflector is used in the most powerful search-lights, there have been many other developments adapted to warfare.  Fresnel lenses have been used above the arc for search-lights whose beams are directed upward in search of aircraft, thus replacing the mirror below the arc, which, owing to its position, is always in danger of deterioration by the hot carbon particles dropping upon it.  For short ranges incandescent filament lamps have been used with success.  Oxyacetylene equipment has found application, owing to its portability.  The oxyacetylene flame is concentrated upon a small pellet of ceria, which provides a brilliant source of small dimensions.  A tank containing about 1000 liters of dissolved acetylene and another containing about 1100 liters of oxygen supply the fuel.  A beam having an intensity of about 1,500,000 candles is obtained with a consumption of 40 liters of each of the gases per hour.  At this rate the search-light may be operated twenty hours without replenishing.

Although the beacon-light for nocturnal airmen is a development which will assume much importance in peaceful activities, it was developed chiefly to meet the requirements of warfare.  These do not differ materially from those which guide the mariner, except that the traveler in the aerial ocean is far above the plane on which the beacon rests.  For this reason the lenses are designed to send light generally upward.  In foreign countries several types of beacons for aerial navigation have been in use.  In one the light from the source is freely emitted in all upward directions, but the light normally emitted into the lower hemisphere is turned upward by means of prisms.  In a more elaborate type, belts of lenses are arranged so as to send light in all directions above the horizontal plane.  A flashing apparatus is used to designate the locality by the number or character of the flashes.  Electric filaments and acetylene flames have been used as the light-sources for this purpose.  In another type the light is concentrated in one azimuth and the whole beacon is revolved.  Portable beacons employing gas were used during the war on some of the flying-fields near the battle front.

All kinds of lighting and lighting-devices were used depending upon the needs and material available.  Even self-luminous paint was used for various purposes at the front, as well as for illuminating watch-dials and the scales of instruments.  Wooden buttons two or three inches in diameter covered with self-luminous paint could be fixed wherever desired and thus serve as landmarks.  They are visible only at short distances and the feebleness of their light made them particularly valuable for various purposes at the battle front.  They could be used in the hand for giving optical signals at a short distance where silence was essential.  Self-luminous arrows and signs directed troops and trucks at night and even stretcher-bearers have borne self-luminous marks on their backs in order to identify them to their friends.