1. Choose a picture with a dark background. This one is from stock.xchng.
2. Create a duplicate layer. Draw a shape in the dark area & erase everything else on the top layer.
3. Click on FX > Outer Glow. Here are the settings I used.
4. Flatten the layers.
5. Filter > Render > Lens Flare > 35mm prime. Move center of lens flare to middle of green glow.
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