You can approximate a linear light source (for neon tubes) by duplicating multiple point lights along a path, using the Duplicate Along Path tool. If you set the lights' distance falloff to Sharp, the effects of the point lights are more localized to the area around the tube. The brightness value of each light depends on the amount of falloff, the number of lights, and the dimensions of your project. It should be set so the combined light from each individual light gets washed out along the path, but doesn't spread too far away from the tube. Offset the lights away from the tube somewhat so that the lights aren't shadowed. Be aware that the tube casts a shadow forward if the lights are offset back from the tube. However, with a sharp falloff and enough distance from the tube to the rest of the scene, this may not occur.

By using the Constant reflectivity shader, you can get an extrude along path of the shape to appear to be a tubular light fixture. Create a texture with a Plain Color shader that is the same color of the lights and set the reflectivity to Constant. On Mac OS X, a good way to set the color of the tube texture is to render the light near a flat surface, like a wall, edit the texture, edit the Plain Color shader, and click on the magnifying glass in the Mac OS X color chooser. This lets you set the color of the tube texture to any pixel on your screen. Clicking on the parts of the wall that are lit by the point lights ensures that the tube color matches the effects from the point lights.