A Light is a great way to try to become lucid. The idea with Light Cue Induced Lucid Dreams is that a sleep mask with little red neon lights is worn over the eyes.
When REM sleep starts, the movement of the eyes is then detected by a retinal sensor in the mask. This then triggers the mask lights to turn on and off for a very short period (You can pick how many seconds.)
This light cue goes through the eyelids and then get's picked up by the sleeping mind, which then shows up as part of the dream.
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It can show up as many things, a flash light or even a UFO.
The appearance of the light in the dream is usually enough to alert you to the presence of something weird happening in the dream and then makes you become lucid.
Two products that let you do Light Cue Induced Lucid Dreams are The Nova Dreamer and REM Dreamer are two products that are well worth looking at, with the REM Dreamer having a two way system to speak back to the device, makes it a better (and even cheaper) buy.