Arduino struggling to power a large LED strip I'm building a word clock and its a grid of 20x20 letters, each with its own LED (I know, its absurd for just a clock). I've recently got the LED's on a strip. Its the WS2812B type, just like the neopixels. There are 3 rolls of 5m strips and a single 1m strip. When I tried to power the 1m strip, everything worked perfectly and all looked quite lovely. But when I tried the 5m strip (just one of them), this happened: https://www.dropbox.com/s/5w1lok6wa7dfvzd/IMG_0046.MOV.mov?dl=0

If you didn't see the video I recorded of it, for a second or two after powering the arduino (uno) on, it works as expected but not long after it all stops the colors and fades to red, sometimes it just instantly jumps to it, like the second time in the video. I don't know what happened but all I can guess is that the arduino is not able to power the strip properly. Any ideas on what I should do to be able to power a total of 16m of these strips?
WS2812 use around 1mA when they are off. So that's already 400mA with no LED lighted. USB can supply around 500mA. So you only have 100mA available. 

Each led package has three colored leds inside; Red, Green and Blue. Every color will use around 20mA when fully turned on.

So you can only turn on 5 colors at full brightness at 500mA. 

Using a 2.5A supply you could go up to 105 colors, or 35 leds full white. 

This would be more than enough for a word-clock, as most leds will be off.