Hi mate. They are currently now in my veg tent under a different light but I think I can still help you.
If you have a smart phone download a lux meter application
Clones and seedlings: 5,000โ7,000 lux
Vegetative growth: 15,000โ50,000 lux
Flowering: 45,000โ65,000 lux
Maximum recommended amount of light: 75,000 lux
This is how I worked out the distance and hope it helps.
likes 2