Maybe you could just make a little blue brush-based entity and give it a minimum light level so it's bright. No need for texture lights.
A tip for anyone asking questions in the forums. If you give a small description of what will that entity/effect really be inside the map, the replies you'll get will always be more helpful. For example, if this LED is going to be part of a computer display, it will probably be different than the single light that marks the location of a lonely button.