yes you can use a hps from start to finish...but it certainly not optimal. all plants benefit from the blue spectrum of the spring time sun, its is only natural...just as the spectrum changes in july to a red/yellow spectrum for flower/fruit. this is what we are trying to mimic in our grow rooms. you should change your bulb from mh to hps only after vertical growth stops, this is a sign that veg cycle is over and the plant is in full bloom.
