A light bulb apparatus has a plurality of LED modules, a substrate, a driver circuit board, a plastic piece, a radiator and a lamp cap. The substrate has aluminum material for mounting the plurality of LED modules, a first connection end and a second connection end. The first connection end and the second connection end is electrically connected to the plurality of LED modules. The plastic piece with a guiding groove is used for inserting the driver circuit board. The radiator has a top plate and a side wall. The substrate is fixed on the top plate, and the side wall are connected to the plastic piece.