and then… 
not having into account Voltage Drop, that was already discussed in my previous discussion, how many leds can I control with an arduino? Lets say Teensy 3.1 or Mega 2560
ps. is this an appropiate question?
thanks!!!
That’s a far more complex question that it seems on the surface.
First off, there’s some raw, absolute limits. Each led takes 3 bytes of ram for the CRGB object for it. The 2560’s 8kb would cap you at 2666 and the teensy 3.1’s 64kb of ram at over 21,000. Of course, the reality is there’s lots of other things that use ram as well so the real absolute limits there are going to be lower. How much lower? Well, that depends on what you want to do and how much other ram you’re going to be using while doing it.
Then there’s a question of frame rate. How many frames/second do you want your animations to update? With the WS2812’s, you’re capped at about 33,333 rgb led updates/second. So, for 30fps, you’re capped at 1000 leds, though with the teensy 3.1 you can use 8-way parallel output to bring that up to 8000, or even 16 way parallel output for 16,000 (I don’t know whether or not 20-way output is currently working).
Of course, that’s assuming that you want to spend 100% of your CPU time pushing led data, which wouldn’t leave any time for computing what you want the leds to show. So again, that’ll pull your numbers back down.
And then, finally, there’s what kind of animation code are you likely to be doing? I have a teensy 3.1 based project with 500 leds that caps out at about 70fps in part because I’m making multiple multi-octave noise function calls per pixel. Meanwhile, Locus was nearly 4000 leds run off of an arduino due that I got close to 100fps at, in part because the animation being run on it was far far simpler.
@Leo_Bettinelli Yes, totally appropriate question. 
very interesting data Daniel! thank you very much for sharing!!!