For these 3 circuits, what Vr are LEDs exposed to ?

 

Zero,

 

Not clear if you mean 20Vrms or 20Vp-p?

If 20Vp-p, then here are all the relevant Voltages and Currents. Note that there is never any reverse voltage across the LEDs, so your reverse diode is redundant.



Same without the capacitor...

 

Thanks.
20 VRMS supply. The LEDs are rated for a maximum of 5 Vr. Are they safe to operate this way considering the negative excursions of the AC ?

 

Did you miss this sentence:

Note that there is never any reverse voltage across the LEDs, so your reverse diode is redundant.

 

You already have a half wave rectifier with a smoothing capacitor. The voltage that the led are experiencing is only positive.