Light Burst in Photoshop

1. Start a new document, and set the foreground colour as #000000 (black) and the background colour as #FFFFFF (white). Now render some clouds (filter > render > clouds).

2. Now apply the Mezzotint filter to this layer (filter > pixelate > mezzotint ). Set the filter to Long Stroke mode and apply.

3. Now apply the radial blur (filters > blur > radial blur) with the following settings. Set "Blur method" to Zoom and "Quality" to Best, also set the "Amount" to 100. This filter will take time to apply on large documents, you can speed things up by decreasing the quality setting.

A simple effect that looks good. To change the colours goto Image > Adjust > Colour balance and adjust the colour balance.