I have to say that I disagree with your premise. There are lots of led tail lights out there that spread the light around. I often check to make sure my tail light is on just by looking at the ground near my rear wheel, if the lights are on, you can tell from that. Incandescent lights have pretty much disappeared, for very good reasons. Not the least of these was that you could be riding along with a burned out taillight and not know it. I'm sure there were incandescent battery powered taillights, but I have to say I've never seen one. Too much power and not enough light. High powered red leds showed up long before they figured out how to make high power white leds, that killed the incandescent tail light a long time ago.