What Induction Means
Passing an electric current through a wire creates a surrounding magnetic field. If a wire is passed through a magnetic field an electrical current is "induced" in the wire. This transfer of energy is the principle used by electrical motors and generators.

With alternating current the magnetic field is changing so a current can be induced into a static wire. This is the principle of the transformer, where current is passed through the primary and induces a current in the secondary coil. Surrounding the coils with steel laminations strengthens the magnetic field and makes the unit more efficient.

The ballast used to limit the current for fluorescent and discharge lamp circuits also uses the principle of induction. In this case there is one coil surrounded by steel laminations. The winding is such that the magnetic field creates a secondary current flowing in the opposite direction to the current from the power source. In alternating current circuits the reaction between these two limits the resultant current.

(This description is a simple non-technical explanation).

Figure 7.2. Components of Genura lamp.

Parts of An Induction Lamp
Genura has a sealed glass bulb, which contains krypton gas, a small amount of mercury (6 mg), and an internal phosphor coating (Polylux 830 or Polylux 827).

The centre of the bulb has a recess into which an induction coil is inserted, so the coil is still "outside" the bulb. There is no wire connection from the electronics through the glass to the inside of the lamp. Sometimes induction lamps are called electrodless lamps for this reason.

The induction coil is connected to a high frequency converter circuit which raises the normal supply frequency of 50Hz to 2.5MHz (M = Mega = short for million). This is much higher than the electronic high frequencies used for compact and linear fluorescent lamps which operate at about 30 kHz (k = kilo = short for thousand).

Induction cooking hobs use the same principle. The hob produces a magnetic field that induces current in the metal cooking pan.

The bulb, control gear, and lamp cap are incorporated into a shape similar to the R80 bulb by using a plastic housing. This housing acts as a safety shield so that the user cannot touch live parts, in