G'day Rolf it doesnt get as cold here as you get but we get down to zero overnight at times. I've found that this setup of 4 x 500w halogen lights gives me good working light and lifts the local working space temperature at a controlable rate by putting the lights closer if need be. I took this photo today and it got down to minus 5 last night outside but you can feel the whole shed is warmer. The downside apart from power cost is that when you turn these lights off after a few days continuous use, most of the globes melt.
regards