ALWAYS use a resistor with an LED!!!!!!! They will not limit the current and need a resistor to do so reliably.
In your case, assume about a 2 volt drop on the LED so
using the 23 volt output, 23 - 8 = 15 volts must drop across the resistor. Assume 20 ma. will make the LED plenty bright with a reasonable life. So, 15 volts / 20 ma = 750 ohms.
and 15 x .02 = 0.3 watts. Thus a 750 ohm, 0.5 watt resistor is needed.
But, I'd try a 1.5K ohm resistor to see if the LED is bright enough. If it satisfies you, this will reduce the heat in the
resistor and lengthen the life of the LED. It will be a
1.5K ohm, 0.25 watt resistor.
On the other hand, you might prefer to use the AC output.
It must be rectified to prevent the reverse voltage cycle from blowing out the LED. Simply put a 1N4001 diode in series with the wire that goes to all LEDs, cathode to the wire, anode to the AC source. Then, 18.5 - 2 - 0.8 = about 15.7 volts across the resistor so the same 750 ohms will work. But, the current will only flow half the time so the LED brightness and the heat
in the resistor will be less. It can be a 750 ohm, 0.25 watt
resistor.
Remember, a separate resistor is needed for each LED.
Ray