You cannot import or export light.
- If you export only a light bulb, then on importing SH3D will tell you that it doesn't recognize the model.
- If you export light bulbs in combination with other models or walls, the model will be imported, but the light is lost.

So, if you need light, you will have to specify this manually in an OBJ or MTL file. As far as I know, there is no manual that explains how to do this.

Hans