It depends on the Athearn, Atlas, and Kato engines and the decoder type. Some engines have regular bulbs and some have LED's. Some decoders will only output 12 volts and blow the LED's. Others will only output 1.5 volts and the incandescents will sit there and not light up at all. I suggest you give Tony's Train Exchange or Litchfield Station a call and ask them, since there's no one right answer. There are decoders that will dual output 12 volts and 1.5 volts by moving a plug or sniping a wire. If those will fit your engines, that's the way to go, since you won't have to change out any headlights.
