It's not the glass or whatever that kills humidity, its the type of heat being deployed from the light bulb. Radiant heat I think is the type we're talking about.I keep hearing over and over bulbs kill humidity. For the record glass does not absorb any appreciable amount of water nor does metal or most ceramic sockets. They only change air flow patterns it remains a matter of balance.
True though glass doesn't absorb moisture either though.
Edit: Actually it might be that fact that there are light photons involved that kill the humidity, not the method of heat transfer at all. Heat pads have radiant heat too and they don't kill humidity, but heat pads also have alot of conduction.