A signal reflector, signal projector or also called Aldis lamp, is a device that delivers a visual signal (optical communication) usually using Morse code – it is essentially a focused lamp that can produce an impulse of light. It is named after its inventor Authur C W Aldis. This pulse is generated by the opening and closing of gates mounted on the front of the searchlight, either via a manually operated pressure switch or, in later versions, automatically. The lights usually feature some type of telescopic sight, and were most commonly used on warships and in airport control towers.

The Aldis projector was pioneered by the Royal Navy at the turn of the century, and continues to be used today on warships. They provide secure communication during periods of radio and other silence, and were particularly employed by convoy operatives during the Battle of the Atlantic. There are several types. Some were mounted on the mast of ships, some small versions ('The Lamp of Aldis') and more powerful ones were installed on pedestals. The larger versions used a

charcoal lamp as its light source, with a diameter of 20 inches (50 cm). They could be used to send signals to the horizon, even in bright sunny conditions. Although it was originally thought that it was only possible to communicate by line of sight, in practice it is possible to illuminate clouds both during the night and during the day, allowing communication beyond the horizon. The maximum transmission speed possible through the use of lights is 14 words per minute.

The idea of ​​intermittently illuminating dots and dashes with a projector was first put into practice by Captain, and later Vice-Admiral, Philip Colomb in 1867. Its original code, which the Navy used for seven years, was not identical to the Morse alphabet but the latter was eventually adopted with the addition of some extra signals.

The Royal Navy and NATO employ signal lamps when radio communications must be silent or electronically 'off'. Additionally, given the prevalence of night vision equipment in today's military, signaling at night is generally done with lights that operate in the infrared (IR spectrum), which reduces the likelihood of detection. All modern forces have followed this example due to technological advances in digital communications.