I have recently installed 6 12v Down Lighters with 20w Filaments using individual 230/12v transformers. All 6 operate from one 2 Way Dimmer Switch rated at Min.Load 60W/VA Max.Load 400W/VA, the second way providing on/off facility at another door. At different light level settings all 6 lights flicker sometimes, although a setting can be found where the flickering will stop. Can anyone tell me a reason for this. Thankyou.