| First glance there would be no difference. Both need to step up the voltage to around 220..240V, so will have about the same length of wire in them.
But the losses are tied to how the ballasts are designed. But also their other properties like cost or mass are tied to how they are designed as well. So you may get lower losses, when you accept heavier and costlier ballast.
With lag only ballast all the windings have to deal with the total apparent power, include the reactive power so about 90VA per lamp and all that translates into losses (at 60Hz the majority is in the wire resistance).
When you go for lead ballast, the capacitive reactive power could be compensated without any extra losses by the gap in the magnetic circuit, so the primary apparent power load becomes lower. Especially when part of a two lamp lead-lag ballast.
But here comes the difference between RS vs preheat: Preheat needs a starting vompensator, which is another wi ding and core. So when the total mass is to be kept equal, the autotransformer on the preheat would hsve to be msde smaller, so will exhibit higher losses. The RS needs no stsrting compensator at all, so the corresponding mass and codt budget could be used to make tge main transformer less lossy.
So when you "normalize" the ballast designs to the same mass, size or cost, the RS will become significantly less lossy. That is the main reason, why the RS concept did wiped out all the F40 preheaters from the market in the "120V world".
In the "230V world" the RS vs preheaters ended up with just a series choke for the preheaters, vs ballast requiring an extra heating transformer or a two winding (loaded with a significant phase shift) on the coil (the "SRS"), either leading to worse losses/mass/cost/size performance.
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