Photoshop Tutorials - Layer Styles - Outer Glow
4) Outer Glow
This style creates an outer glow effect for the layer image.
The standard option for is the Blending Mode. Screen seems to be the optimal mode for this style. There is the Opacity option for this effect as well. With the Noise slider, you can set the heterogeneity of the glow. You can set the glow color just as the shadow color. By default the glow is the gradient from the color you have selected to the transparent white. But you can chose other gradient or create one for the glow.
The Technique dropdown menu lets you select the type of shine - Soften or Precise.
Spread slider sets the softness for the glow edges if the Soften technique is used and it is not influential when the Precise technique is used. The Size slider sets the glow size.
In the Quality section, you can set the contour of the shadow from the Contour dropdown menu, then tune it with Range, and Jitter sliders.