Quake3World

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That's a pretty big value for q3map_lightmapFilterRadius, try something like 0 8. Other than that, I don't see anything glaringly wrong with the shader. Also check that you don't have any syntax errors in this or other shaders.

Reference:
Shader Lighting Experiment
Q3Map2 Shader Manual: Light Emitting Shaders

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If your revert back and comment out all the new changes, does it still work? You are using the latest version of Q3Map2, right?

The shader itself looks right, so I can't help thinking that something else is causing the problem for you.

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Curious... if you want, you can upload the entire shader file and I'll take a look at it.

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I tested the shader and it seems to work fine. But it looks like you solved it on your own. What was the problem?

For jagged shadow edges, try slowly increasing the filter radius value. Too much and you lose definition (your shadows will look like a big blur).

You can also combine this with an increased lightmap resolution which you can set per func_group, shader or globally using compile switches. But keep in mind that increased lightmap resolution increases your BSP size as well as taking up more texture memory, so there is a performance cost.

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Try using a value like 4 (higher res) or 8 (lower res) for the -samplesize switch during the bsp-stage of your compile.
sth. like: Another option would be to add the _lightmapscale key to the worldspawn entity. Something like 0.125 should be really sharp, but beware of compile times then. Maybe that helps

Check out the links I posted above. I spent quite a bit of time documenting this and you can see the resulting changes in the screenshots.