• Press D (should make colors black and white)
• Filter / Distort / Render Clouds
• Filter / Distory / Render Difference Clouds
• Image / Adjust (or adjustments) / Invert - Or, try Ctrl + I
• Image / Adjust (or "adjustments" / Levels - Or, just try Ctrl + L. Slide the slider and make the background darker and the lightning darker.
• Image / Adjust (or adjustments) / Hue/Saturation - Or, just try Ctrl + U. Check "Colorize" And fool around with the settings slider.

And then you've got lightning.