Traditionally, tungsten HID electrodes are activated with thorium oxide alloyed into the wire. This thoria doping reduces work function for lower cathode drop. This was also done for TIG welding electrodes for the same reason. Thoriated tungsten TIG electrodes are falling out of favor for other formulations, most notable lanthanated tungsten electrodes. Looking this up, it seems an identical change has been observed with HID lamps. Instead of thoria, you just use lanthanum oxide (lanthana?)

I have never heard of lanthanated tungsten outside of a welding context. Lanthanated tungsten has a higher work function than thoriated tungsten, so performs slightly worse in terms of voltage drop. Is this performance loss also observed in newer lamps that (presumably) use lanthanated electrodes?

Did this thorium to lanthanum transition ever really happen for mainstream HID lamps, or was it just for some niche lamps where lanthanum was used?

I also discovered that pieces of TIG tungsten can be used as HID electrodes because they are doped for the same purpose at pretty much the same percentages. I highly doubt I will ever find myself making my own HID lamp, but I will keep that in mind in case I ever get rich enough to have the equipment necessary to do that.