Induction coil core, illumination unit using the same, and polycrystalline ferrite

An illumination unit comprising:

• a bulb containing discharge gas inside;
• an induction coil for generating an electromagnetic field with a frequency in a range of 50 kHz to 1 MHz is disposed in the bulb;
• and
• a power supply for supplying power to the induction coil,
• wherein the induction coil includes a core and a winding, and the core is made of a Mn—Zn polycrystalline ferrite and has a Curie temperature of 270° C. or more, and
• wherein the Mn—Zn polycrystalline ferrite includes an Ni element as an additive,
• the Ni element occupies 1 wt. % to 6 wt. % of all elements excluding oxygen in the Mn—Zn polycrystalline ferrite.