Re: Opinions ? Informed advice ?

I have HID dips in my Rover SD1. But different actual headlights too - so they give a decent MOT passing beam pattern. Simply fitting HID bulbs to existing units may result in poor beam control due to the optics not being designed for them.

You also need the lights to be either self levelling - or the car suspension to do this. And headlamp washers.

I don't think Halford sell Xenon (HID) units. Just blue tungsten ones to look a bit like them for boy racers.

Assuming your reflectors are good, try Philips Vision replacement bulbs. And measure the voltage drop from the battery to lights - both 'live' and ground. It's often considerable with an older car and cleaning connectors or even adding a relay can improve things dramatically. The light output seems to follow some sort of inverse curve versus voltage.

The other benefit here with the HIDs is the ballasts obviously run off a regulated voltage supply. Which means they give the same output regardless of battery voltage.

I remember the first low pressure sodium arriving when I were a kid. Probably replacing gas - which we still had in our street. They started with main roads first.

And that low pressure sodium had a very narrow spikey spectrum. My maroon bike looked black in that lighting. So everything became sort of monochrome - but not black and white. Very odd - but forgiven since you could now see things. ;-)

Of course later high pressure sodium was much better. And there are now all sorts of discharge lamps - think cars with HID, or film HMIs, and CSIs etc.

And of course fluorescent can be very good indeed with specialised tubes.

I'm sure LED will be as good one day given the research and investment. But I don't think it's there yet.

The other thing as you pointed out is they can look very bright indeed when viewed directly, compared to other types. Even when the incident light is the same or less. Which is not what you want for street lighting.