You'll need to find the light footprint map provided by the lamp's manufacturer so you can see what intensity the light emits at certain heights. During veg you'll want around 300-400 PPFD.
Again, the light manufacturer should supply a map showing that PPFD the lamp emits at certain heights.
You realize you're not giving us a lot to go on. An image hardly shows your setup accurately. We'd need the lamps name or at least it's power draw.
Generally speaking, low-power lamps of ~100W should be hung about 50 cm from the plant during veg (depending on how much PPFD the lamp produces).