How do telephone powered lamps work?

Question

How do telephone powered lamps work?

Answer 1

There's 25 volts AC present on the line pair in the phone line constantly, so the lamp simply uses that power to feed a small bulb.

Answer 2

There is 48 volts DC on your phone line when it not being used.  But I'm not exactly sure what you mean by a telephone powered lamp.  If you draw current from your phone line the central office (CO) equipment may think the phone is off hook and try to send dial tone.  So you can't draw very much power from the phone line to light any type of bulb.  Do you mean the lights used for a ringing signal for hard of hearing people?  The CO equipment sends 70 to 90 volts AC as a ringing signal.  If you have hard of hearing lights, this is what powers them.