For it to work best, you also need to go into the material and turn OFF the "cast shadow, recieve shadow, and self-shadow" options in the material. Glowing things with shadows across them just do NOT look right. It's really important to do this with the material on any object that is supposed to be giving off light, such as flames, etc. In addition to the material looking more realistic, if you then stick a light source inside it, the light can radiate outward unobstructed.