A trench type power MOSgated device has a plurality of spaced trenches lined with oxide and filled with conductive polysilicon. The first lightguide plate is configured to satisfy the condition of t1<t2\u2266t3, where: t1, t2 and t3 are the respective heights of the light exit side surface, the reflecting side surface and the light entrance end surface. In one embodiment, a method includes separately performing a first one or more arithmetic operations and a second one or more arithmetic operations.