While flying out of Tennant Creek I had occasion to do several night landings there. The main runway (07/25 by memory) had T-VASIS lights fitted. I soon became aware not to trust them after finding myself low one night with over a mile to run to the threshold. The area is subject to earth tremor movement and the lights would soon be out of alignment (a common problem with T-VASIS as the boxes are all separate). As the majority of my approaches there were visual circling approaches I used to use height/time/distance to judge the turning points and then trust my visual appreciation of the runway lights.