8 led NEOPIXEL strip bargraph display

Hello,

I am trying to get a strip of 8 neopixels to rise from 0 up to 8 proportionally to a analog voltage range from 1.5v - 5v I understand how I can map the input voltage but I cannot find a way to drive the neopixel strip like that. simple would be to use a POT and have the arduino read the pot and light the leds sequentially until all are lit at 5V

I need to know how I could map the voltage to the neopixels. can you point me in the right direction ?