2x100w Incandescent series, series 75/80w mercury vapor
My way of powering up a 75/80w mercury vapor bulb, it is using a 175w MV ballast, then (all in series) 2x100w incandescents, then lastly a 75/80 merc. I wasn't able to find any ballasts for that kind of merc bulb, so I did some math (175w (ballast coil )- 100w incandescent = 75watts to the merc bulb!)
Nope! If you connect two lamps in series, they will share the supply voltage between each other. Since both are the same power, they will get around 60V each on 120V (or 120V on 240V), but if they have different wattages, the voltage on each one will be different.
In other words, when lamps are in parallel, voltage is the same on all lamps, and current changes with the number of lamps. In series, the current is the same on all lamps, and voltage theoretically changes with the number of lamps. This is still true for series streetlighting systems, but since all modern electric grids work in parallel, voltage won't change, so the more lamps you connect the series, the less voltage each one has.
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In other words, when lamps are in parallel, voltage is the same on all lamps, and current changes with the number of lamps. In series, the current is the same on all lamps, and voltage theoretically changes with the number of lamps. This is still true for series streetlighting systems, but since all modern electric grids work in parallel, voltage won't change, so the more lamps you connect the series, the less voltage each one has.