They have been around for a couple of years as screw in bulbs. GE started offering LED lighted numberboards several years ago, but they proved too bright so now a yellow lens is placed in front of the LEDs to tone it down a bit. I wish you could buy screw in LED bulbs for home use that are as bright as the ones that they are using in the step lights. Locomotive bulbs are either 75 volts or 32 volts depending on the design of the locomotive.
Main push to use them is that they last much longer than regular bulbs, but they do cost much more. (reducing energy consumption helps too, quite a difference when all bulbs (running boards, engine room, stairs, number boards etc--batteries last longer when someone forgets to pull the switch.)