My HPS keeps my plants small and bushy as i get the light as close as my plants as possible. I also start vegging for the first 2 weeks on a 24/0 photoperiod to keep them small and bushy and if you then switch to 18/6 thats when they will stretch as the plants stretch during your dark period looking for that light. If you vegg on 24/0 the plants wont stretch and will keep small and bushy with plenty more nodes. I do my first 2 weeks on 24/0 then switch to 18/6 to get some height on them and when they are around 12" tall i start my 12/12 until the end. I use a 400w (bulb shown below) and this plant was ready in 92 days from seed packet to harvest growing the way i just explained.
the bulb.
http://www.greenshorticulture.co.uk/Grow-Lights-182/Grow-Lamps-192/Dual-Spectrum-Grow-Lamps-806.asp
The growlux sunmaster is my choice.
the plant.