Lucas 464A Rear Lights - best colour for interior reflector?

Assuming these are tail lamps? I’d attempt to line them with chrome tape or vinyl to boost the visual output, they were painted white as it was probably the most cost effective reflective colour at the time. If you can line them with something shinier it’ll go a long way towards rearward visibility without detracting from the aesthetics of the original fitting as you won’t be able to tell when they are assembled.

Colour isn’t really important as long as it’s bright and reflective of the colour you are trying to reflect- white being good and chrome being best. If you can paint them the most reflective ‘chrome’ you can that will work better than white.

Opinion seems divided right down the middle on this one (offline and on) as to whether white or silver/chrome is best. However, since the reasons for using white offered are the same as Colin explains above, I'm inclined to think it's the better option. I also like the suggestion of painting each one a different colour and then testing them side-by-side so we can get a nice definitive answer. They are incredibly easy to wire up thanks to the sprung wire clamp fitting on the back so I can test them very easily off the car. I'll be sure to share the results once I've tried it so we can see what difference, if any, there is.

The other thing to consider is are you going to stick with incandescent or use LED bulbs, LED's will be brighter and use less current, an easy way to make sure you are seen better but obviously not original. Type of bulb might have an impact on the best reflector colour.

I'm sticking to incandescent bulbs for these since that's what they were designed to work with and we'll be supplementing with some hidden high level LED lights so there's not really any need to put LED ones in the original fixtures. That also gets around any of the issues in trying to find the correct sort of LED bulb to work best in these fittings.

Not too fussed about fitting an extra reflector bowl at the moment, I imagine it must be do-able since you can get separate sidelight innards and the like. I suspect a reflector bowl might make a bit of a 'hot spot' visually rather than a nice diffuse glow, though I could only prove that suspicion by fitting a reflector bowl, of course.