How to improve flash time on lights controlled by solid-state relay via Arduino?
If you buy your parts from proper suppliers, they will provide dasheets for things like your relay.

Checking the datasheet for the relay,we find this bit of information on the switching time:



You are using a 210B relay, so it should take it at most ((1 second / 60 Hz)/2 +1 millisecond)= 17 milliseconds to turn on.  It should take at most (3*(1 second / 60 Hz)/2 +1 millisecond)= 26 milliseconds to turn off.

That's on and off at 23 times per second, so the relay should be fast enough.

Now lets look at the LEDs.  This is a consumer article rather than something you would buy from an electronics supplier.  The only "specifications" available are whatever the seller feels like putting in his advertisement.

The key point is that your string of LEDs is microprocessor controlled, and that you seem to be controlling it by switching the AC power on and off.

The output from the transformer doesn't shut off immediately when you disconnect it from AC.

The LEDs don't go on immediately when the power comes on because the processor has to start up and prepare to do its thing (it flashes the LEDs itself normally.)

What you'll have to do is to leave the AC adapter plugged in all the time.  Cut the wire feeding the LED after the transformer, and put your relay in series with that.  Set thr controller to "always on" and you should be able to flash your LEDs at speed.



That assumes that the LEDs are "stupid."  There are LEDs that contain a small processor themselves, and you can't just chop their power and be happy.

In that case, you need a different string of LEDs with plain old fashioned stupid LEDs.