this maybe a stupid ? but...

this probably sounds like a dumb question but i currently grow using a Philips 400w son T -Agro light bulb with appropriate ballast/reflector..am i correct in asuming that any brand hps 400w bulb will suffice ? eg..can i use a 400w (growlush bulb) instead of the philips brand...ive noticed that other brand names are cheaper ...i do not want to compromise on quality for sake of price...though i suppose all bulbs with the same wattage would be ok?

Yes you can. As long as the wattage is the same and obviously the fitting for the reflector you can use any bulb brand

On quality, i hear Sunmaster bulbs are very good, with there 600watt putting out 95000 lumens. Not sure bout 400watts tho. Dont know if you can get them outside UK.

cheers thanks for info