Is it correct that the earliest clamshell streetlights like the OV-20 had optics that were designed for tubular shaped clear mercury lamps that are no longer available?

When did they change to bulb shaped?

When did phosphor coatings come out and are some better than others?

Are Westinghouse Lifeguards the best ones ever made?

Is their any difference between North American and European mercury lamps aside from wattage?

Is it correct that the earliest clamshell streetlights like the OV-20 had optics that were designed for tubular shaped clear mercury lamps that are no longer available?

When did they change to bulb shaped?

When did phosphor coatings come out and are some better than others?

Are Westinghouse Lifeguards the best ones ever made?

Is their any difference between North American and European mercury lamps aside from wattage?

I can answer 2 of those:
1: The modern EYE lighting mercury vapor lamps are of better quality than the Westinghouse Lifeguard, though they do not have anti-blackening electrodes
2: The only differance in European lamps is the base. e40 is slightly longer that e39, but will still fit in an e39 socket.

Idk about the OV-20, but the form 400 had a magnetic arc deflection cool for the tubular ah-1 mercs of 400 watts, but I don't know why.
The European 700 and 1000 watt mv lamps are meant to have a supply voltage of 250 in most cases, but outs are meant to have 350+.