nobb

Where did you find a 1.2mm wide led? Are you sure a 1.2mm wide led can produce 2500mcd? Thats a very small led.

By 300 leds, I am assuming you are doing the top and the bottom. It is going to be a real pain to solder up all that, you might want to just try going with one edge first just to test it out. So 150 led's an edge. But keep in mind these leds are very tiny and its going to be surgical work to be able to solder 150 of these leds back to back. So realistically, maybe 100 leds/side is more feasible.

I'm not exactly sure how they do these mcd ratings, but you definitely will not be getting 75 000 mcd total. I think each of the 2500 mcd coming from each led will have to be diffused and spread out across the whole area of the panel. Dont know how to do the math on this one. You probably should start off with the brightest leds you can find, rather than going with "dimmer" leds. If you find the panel is too bright, you can always desolder some leds. Its easily to make a bright panel dim, but you cant make a dim panel bright, so maybe its better to be safe than sorry.

Also, what were your plans to arrange and support these leds? For my case, I was thinking of using two parallel strands of wire then solder the leds in parallel sort of like a ladder. Then use clear epoxy on the back of the led as structural support. With this method, you could arrange more leds to a side since you are using the width of the led but the downside is you will need 2.5v at a fairly high current. Or maybe I was thinking to have the leds in series then use diodes to rectify the high voltage AC output from the inverter to a high voltage DC for the leds.