iLightningCam uses true real-time recognition of lightning strikes. Once recognized, your iPhone takes a picture of the recognized lightning in up to 8MP (camera mode) or full HD (video mode). 
You only need a good view on a real thunderstorm.

The app works free hand. Just point your iPhone towards the scene/part of the sky/thunderstorm where you expect the next lightning, start the app iLightningCam, choose video or photo mode and wait, the app will automatically press the trigger/shutter if a lightning is detected in your view. Usually this app retails for $0.99/£0.69 but today you can pick it up for free. Click here to download.