When to change to a 600watt

[tyroncurtis42]

Ok, so I have been using a 400 watt MH for veg, I now want to switch to a 600 watt HPS for flower. At what point do I change the bulb? Do I change before the lights are due to go out or do I change while it's dark in the tent? The only reason I am asking this is because it's pretty dark in the room where my tent is and I can't see a thing. Now if I turn on a light when the plants are in darkness it's going to interrupt the light cycle right? So how do I do it? I'm so confused.

 

[Merkle420]

Can you turn the 600watt on then turn the 400 off?-.-

 

[Donald McGonagle]

You could turn the plant light off an hour early, giving it time to cool, while you have other lights on in the space to see what you're doing. Shorting the plant 1 hour of light will be ok.