What is the purpose of 2 diodes on the bottom, i see none?

It is a dimmer circuit, in case you didn't recognize.

light emitting DIODE

"D1 is a rectifier, allowing only forward bias current to flow in the circuit" i thought that but clearly LED is conducting in other direction so we can't speak of rectification.

I knew LED is an indicator, i was really asking about left one.

I know what Zener diode is and how it works, actually i studied it in great depth. Don't assume it's zener when it's not zener symbol.

Also there is R1 and variable resistor to limit LED current

I mistakenly wrote the last update, R1 and variable resistor don't limit the LED current since there is TRIAC gate current, i wonder why is there no resistor for it.

I agree D1 is probably used to provide low voltage for LED.

I find it strange there is no resistor at TRIAC gate (like at amp transistor base/gate). I see nothing to limit the gate current except the load and R2.

Answer is R1+VR1 and C1+diodes act as voltage divider, most of the voltage falling across R1 and VR1 thus limiting the voltage and current at DIAC and TRIAC gate. In fact this is the basic of how dimmer works, variable resistor changes how long it takes for C1 to charge up and fire up the gate.

So there was no need to correct myself above, R1 and VR1 DO limit the LED current.