I have installed many HF ballasts from Osram. Are you talking about TLD lamps or are you reffering to the new TL5 lamps? If you're reffering to TLD, then make sure that the ballast is a "warm ignition" type. I think that your main problem at low temperatures would be at the ignition of the lamps, since once it's lit there is a certain warmth from the lamp itself which should keep it lit. Another point: If referenve to TLD, then there are special TLD lamps for low temperatures. Personally I prefer the Ballasts from Osram but the lamps from Philips. I would advise you to check out their website. Since you are talking about fittings with IP66, then I would advise to look for that too by Philips, since Osram don't do IP66 Fittings with HF ballasts.
