How do you get 2xVf?
I found the LED drop voltage of 2Vf using a resistor in series with the 15V power supply. Voltage across led was 2V.
The diodes are in anti-parallel. When the line polarity is in one direction, one diode conducts aad drops ~1.2V. When the line polarity reverses, the other diode conducts and has a drop of Vf=~1.2v, but with the opposite polarity. One set of 3-series diodes functions with one LED and the other set of 3-series diodes functions with the other LED. Since the resistor is not polarity sensitive, it functions half the time with one LED, and half the time with the other...on opposite polarity line cycles.
Yes, I noticed this. I used the DMM and it read 2.07V across the diodes just like you say. Or just 2V
The Max rating is what they "can" dissipate, not what they "will". So, If your lamp draws ~100mA, and each diode drops ~0.7V that's 0.7Vx0.1A=0.07W (70mW) per diode. And since as you say, they only conduct half the time, that's an average dissipation of 35mW per diode.
That makes sense. I will put in 120AC to this thing and see if I don't burn the house down.