also, i vow to never again post any diagram that is not explicitly in full schematic format. i was trying to save some effort
Childish drawings do unfortunately the exact opposite. Only *duino folks, that can't do any better, need them.
in the words of Elon Musk, "Framing the question accurately can often be the hardest part of any problem".
Yes, exactly this. If you are an electrician, you know how to draw a proper schematic for an engineering forum.
But regarding your goal:
First, what frequency of PWM does the RGB sequencer output? Only then can one decide of the appropriate power switching device and signal conditioning. (for example, passing a higher frequency PWM through conventional optocouplers is not possible, they are quite slow. Motor inverter IGBTs are also usually switches on the slow side, etc...)
Second, why a 240V LED string? That sounds odd. Have you made one yourself? Or have you just soldered a bunch of 12V ones in series? Who will be the end user of that contraption? If just you, then likely fine, you electrocute yourself. But mind you, as an electrician, you shall know about safety a lot. So how are you going to insulate the LED string from a dangerous contact with the end user or even a random lab visitor? Conventional 12V strips are nowhere near safe to be used beyond what is ELV voltage. Removable plastic LED strip cover ain't gonna do it, because removable and the led strip substrate does not have the required dielectric strength against the mounting substrate, which for LED strips may as well be aluminium - unacceptable. Think about this.
Also, what for? Even a 5m long string can be fed from just 12V (depending on their power rating of course, some may need shorter sections reinforced with external higher capacity wiring). 240V seems very very excessive.
Where are you going to get 240V DC? Just by rectifying mains directly? How about the resulting 100Hz flicker? Adding any filtering capacitance will increase the output voltage, up to sqrt(2) times your input (340V) and also decrease power factor, which, at least in Europe would be problem if the device would need certification.
