Mark is probably right, they are probably knockoffs. Thats not to say they arent a good cheap alternative. Bulbs often break, especially if moved when hot, and always avoid knocking. Im sure youre aware of this, but its good to look at the basics. Also when changing bulbs, depending on the type of bulbs make sure you dont touch them directly with your hand as this can shorten the life of the bulb.
Im in a similar situation; im from a lighting background, and am used to using high end quality lighting. Unfortunately starting up on my own has been a considerable cost as it is, and things like editing suite and camera you cant really go cheap on. Now looking at purchasing a basic lighting kit myself I am in a dilema whether to buy what I know is good and spend £1500+ or look at the cheaper alternatives, where i could get a 3 piece lighting kit with stands for around £300. Something I have read recently is using construction site halogen lights, these lights are 500w with stand and can be purchased for >£30. Ok, these wont have barn doors, and will not be able to be directed, but for broadly lighting a scene these could be a great, cheap, alternative.
If you have the cash, purchase a 3 piece arri set, 2x300w & 1x650w, grab some filters and scrub, and youll be sorted.
Good luck.
Lloyd Morgan Productions
http://www.lloydmorganproductions.co.uk
Video Production Dorset UK