right now im using CFLs but my friend has a brand new 400w hps that hes not using and he says i would be able to use it... good idea for an apartment?

yea its perfect but make sure u have the right bulb and enough fans and exaust fans to take all the heat from the lamp out the grow area my first time using HID had a little of high temp probrem remeber use ur hand to find out how high to put the light wen it burns ur hand its gon burn the plant 400watt its about 12 inchs away for top

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Yea. You need a ballast of the same wattage too. Also, make sure you don't handle the bulb with bare hands! Make sure its clean when he gives it to you. You don't want an explosion just as you plug it in...