The level shifter is used to change logic levels from 3.3v to 5v. So regardless the 74HCT125 should be powered with 5v as 5v logic is what the ws281x leds require.
The level shifter is used to change logic levels from 3.3v to 5v. So regardless the 74HCT125 should be powered with 5v as 5v logic is what the ws281x leds require.