El-Vak Lucifer T375W sunlamp
INDUCTIVE-IGNITION
Other than making a direct contact
between the electrodes of a discharge
tube, the discharge could also be started
by a temporarily increase of the field
intensity around the cathode, a so-called
inductive ignition. For this purpose a coil
was mounted around the outside of the
discharge tube, around the mercury pool
inside the tube. Through a switch and a
capacitor, the coil was temporarily
connected to the voltage source.
Disconnection of the coil, caused a short
voltage peak and thus a local increase in the field intensity. This field triggered a glow
discharge that, instantly or after some repeated switching, developed into an arc
discharge.
In later designs a push button (S in the
diagram) started a relay circuit that
repeatedly opened and closed the switch
until the start button was released. A little
transformer T in series with the cathode
induced a voltage pulse, a method that
was also applicable for high pressure
mercury vapour arc discharge tubes that
lacked a pool of liquid mercury, like the
El-Vak Lucifer T375W sunlamp on display
here.
