Trouble with Holes

I've been trying to cut holes in the tiles for the floor lights in the dining room...unsuccessfully! I bought some special cutters for the job and they worked fine for the holes to allow pipes to pass through in the shower. However, the holes for the lights are big, 10 cm. So, having tried and broken 3 tiles I've decided to cut the tiles in half and have a semi-circular hole in each half.

Once I've sorted out the lights I'll have done about three quarters of the floor.