is it safe to drive 8 ws2812b's from an arduino's 5v pin
As long as you make sure the max draw of full RGB white is not drawn for all 8 at any given time, you should be within the Limits of the on board 5V regulator. Since this draw depends on your code, you can easily make sure that all 8 leds are not on 100% full draw at the same time. At 65 ~ 70 mA full draw, (20mA red, 20mA blue, 20mA green, and &lt;10mA for the WS2812 itself) times 8, a 525 to 560 mA load at full white, you could have 7 fully on at any given moment without major malfunction. The ATMega on the Arduino itself should take under 50 mA worst case.