Abstract: An inner coupling electrodeless lamp comprises a glass bulb and a power coupler. A cold end of the glass bulb is provided with an amalgam. The glass bulb includes an external portion and an inner portion. A gas discharging cavity that is annularly airtight is defined by the envelopment of the external portion and the inner portion. The gas discharging cavity is full of inert gas. A coupling cavity is defined in the inner portion. The power coupler includes a radiating post, a ferrite core, and a winding sequentially situating from an interior to an exterior thereof. The power coupler is disposed in the coupling cavity. At least one diffuse reflection layer that is made of a material falling in a 250˜2000 nm spectrum scope and containing a high diffuse reflection rate larger than 30% is disposed between an inner wall of the inner portion and an external surface of the coupler.