Extractor fan relay for two independent light switches

[mainline]

That's it. But both lights must be on the same circuit.

It's quite common - some applications use a purpose designed DC coil, some use an AC coil and just feed it DC. Heatmiser do the latter in their UFH control/wiring centers.
Since it's only half wave, and relies on the coil inductance to maintain the current for over half of each cycle (so it's not smooth DC, and significantly less effective voltage than full-wave & smoothed), I doubt it's particularly bad for the coil.

https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3250_AppNote&DocType=CS&DocLang=EN

 

[Simon47]

https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3250_AppNote&DocType=CS&DocLang=EN

Interesting document thanks. But it neglects the half-wave rectification, and also totally neglects the effect of the coil inductance when presented with a non-smoothed rectified AC. In practice, the effective current throught the coil will be considerably lower than a simple I=V/R calculation might suggest.