Depends how dim they are at how cold. Unlike auroreborealis a CPF cyclist from the Yukon, I can let -20 C or -10 F go as not worth the trouble. He can have cylcing at -40 (same both scales).
The down low glow lights are about $150 for two tubes, one battery. They seem too bright and would hurt night vision used as side markers on the forks and seat stays. If these CCFL's were dimmable in warm weather and bright enough in cold, the run times and price make them look very interesting as marker lights. The SuperFlash lights do their thing well when cold and when you factor in the AAA cells, also cheap.
Do you have brand and model number? There may be other sources to Google.