Mount your camera on a tripod or sit it down on a very sturdy base so to get no movement of the RX100III when taking shot.
You will need to use “Bulb Mode” when taking the shot. It allows for long exposure times to capture streaks of light.
Bulb mode will let you hold the shutter open as long as you wish. This allows the movements of light to be photographed, like fireworks, auto lights, planes landing at night.
Keeping the RX100M3 as still as possible makes or breaks this technique. Using the free remote app (Sony Playmemories) will eliminate all shake and movement. You will control the shot from your Android or iPhone.
Use these setting on your RX100III:
Set the mode dial to M. (Manual)
Connect your phone to the camera using Wifi or NFC.
Dial exposure time to Bulb on the app.
Dial in a suitable Aperture value from F/5.6.
Press the shutter button on the app to start the exposure.
Press the shutter button again on the app to stop the exposure.