UPDATED - MAJOR CHANGE due to new information:
WARNING The question has probably been misinterpreted by everyone (including me) due to a lack of complete information. I/We thought there were 20 series LEDs per string and that the OP's diagram showed the WHOLE LED setup and that each LED shown was a 1.2W unit.
With the added (clear and nicely lit and focused) photos it now seems likely that:
- Each "light: has 12 series LEDs.
- Each light is 1.2W so about 100 mW per LED so ABOUT 33 mA/LED and very roughly about 40V DC per light.
- A total of 20 lights = 20 x 12 = 240 LEDS is proposed.
This changes several major things.
Power per light is 1.2W, so a stabilising resistor can be relatively low power.
V_string_DC inside a light is now 12 x Vf_LED or maybe 36 - 40 VDC.
With added headroom voltage to keep LED current relatively constant a DC voltage of 45-50 Vdc would be adequate.
STILL RELEVANT. Lightly edited.
DANGER The original circuity is lethally dangerous and should NEVER be used for something like garden lights. ALL parts of the circuit should be considered as being at full mains potential as they at any time may be.
This type of supply is only suitable (if then) for circuitry which is always well insulated from human contact. Garden lights don't usually qualify!
IF the mains voltage is fed into a light by manufacturer approved wiring that meets relevant regulatory code and if the light also meets code then it MAY be OK - but is not a good idea.
For 50 VAC remove (short) R1 & C1, select R2 as required and place a large capacitor on the LED side of R2 to remove the flicker. If 50VAC used Vdc_vpk is about 70 Volts = 70/20 = 3.33V/LED. May be marginal depending on LEDs used.
With each light needing 45-50 VDC an AC 50V feed is rather higher than desirable.
See below for voltage sizing.
If using two strings in parallel as has been suggested would lead to much greater dissipation if 50 VAC is used.
IF you have a choice of VAC then testing the LEDS at desired brightness and current will allow a suitable value of VAC. R2 is set internal already and can be left unchanged.
Operate a light from a DC supply with R1 and C1 removed (shorted).
Vary supply to give about 1.2W dissipation. This will be at ABOUT 40VDC.
Determine Vac to give the above DC value.
Choose a per light filter cap OR a per whole 20 light feed filter cap (much larger).
Per light cap probably 100 uF plus.
Per whole string maybe 2200 - 3300 uF