the Philips Biosol 11856 sunlamp was ballasted with a heavy coil in the base of the armature
Philips Biosol 11856 sunlamp
For an AC operated sunlamp, a coil could be used
as a ballast instead of a resistor. Unfortunately coils
that need to operate at the relatively low line
frequencies of 50 (Europe) or 60 Hertz (USA) were
heavy and expensive but this disadvantage was
often more than compensated by the gain in power
efficiency due to the reduced power dissipation.
Another appreciated advantage of a heavy coil was
its ability to stabilise the armature mechanically
when placed in the base of the armature, as with the
Philips Biosol 11856 sunlamp on display here.