the Vari-Pac 3-way heat lamp contained two separate filaments in the same bulb
Vari-Pac 3-way heat lamp
The electric circuit of a heat lamp for therapeutic
use did not differ from that of an incandescent lamp
for lighting purposes or that of an electric heater: An
AC- or DC supply voltage, connected to the two
leads of the infrared source directly or through an
on/off switch and/or a safety fuse. Some Kanthal
elements consisted of two or more sections that
could be selected independently or in combination.
In rare occasions, like with the Vari-Pac heat lamp
on display here, an incandescent lamp with two
separate filaments in the same bulb was operated in
the same way. Using a 3-pole socket and two
filaments, one of 100- and one of 150 Watt,
connected in a V-configuration, a wattage of 100,
150 or (by connecting both filaments to the supply
lead) 250 Watt could be selected.