aiming reticle illumination light

Greetings all

I hope someone can help me and I hope I'm in the right forum for this.

I have a pair of Carl Zeiss 8 x 60H binoculars my grandfather brought back from WW2.

On the side of the binocular body there is a fitting that takes a light source to illuminate the aiming reticle at night. I have been told by a reliable source that the light source would have been about 5 watts. The internal diameter of the fitting is 15mm  (0.59").

I am wondering if anyone can advise/suggest a particular bulb and socket combination and a seller. I am hoping to run the light from a AA pack (?). I have looked at several sites online and found various bulbs, but none seem to match the parameters I need (ie right wattage, but 28V, or 6V but too big/small). I have also considered an LED bulb, but I don't know how to convert wattage equivalants to LED (I know a 5 watt LED would be way too bright). An LED would be ideal, if anyone can point me to instructions and particular parts and how to wire it.

As far as the fitting for the light goes, I'm pretty handy and am confident I can rig some sort of fitting or sleeve. It won't be a permanent fitting, as it wasn't designed to be.

In the image below, the fitting is on the side of the right binocular body. Please excuse the dirtyness. They've been sent away to be cleaned and serviced by a professional optics company.

Thanks in advance for any help or advice.

Regards