Quartz glass is transparent to ultraviolet light, and emits large amounts of ozone and UV light as a result.
If the tube contains mercury, it will produce a lot of UV. A lot of suppliers choose to add mercury on purpose because it will make the tube light up very strongly. But ours only produce a very small amount of UV, therefore emitting very little ultraviolet light.
Both phanotron tube and long straight tube do not use mercury inside.
Source: Spooky Central Q&A