I got some bulbs from Carley Lamp in 4.8V with a PR-style flange base to put in my 4D Maglite using NiCd cells about 25 years ago. Carley Lamp is/was a specialty bulb manufacturer that would make just about any bulb you could want. I'd bet bulbs on the space shuttle were made by them. Anyhow, they offered a range of wattages, so I think I ordered them in a 7W rating. They were bright all right, but they also caused the aluminized plastic reflector to crinkle from thermal expansion and slightly melted an 1/8" dot in the middle of the plastic lens. They had lesser wattage ratings that I should have ordered, but I said let there be light, and there was light...and heat...and plastic melting. I don't know if they are still around or are doing LEDs these days or whatever, but they were the bulb experts back in the day.