... if you're running a 400w MH, you're currently getting around 30,000 to 40,000 lumens, and prolly round 4100k colour temperature. Great for vegging.

If / when you switch to the 1000w HPS, you'll be getting around 140,000 to 150,000 in the same space (and at a nice 2000-2100k colour temperature; better for flowering), so I'd make SURE you have good ventilation, and some headspace for the flowers to explode in

And a good set of sunglasses to wear while gardening