CD burners work using a transparent dye that replaces the aluminum strip in CD. The dye becomes opaque when its exposed to heat. The units are equipped with a write laser that is stronger than a read laser on a CD player. The write laser uses the same path as a read laser, but only the intense heat from it will imprint spots of opaqueness onto a burnable CD. These spots are read in the same way as the bumps are. The remaining transparent areas reflect light back to the read laser source and the data reads as 1’s. The opaque areas exposed to the heat bounce the read laser away and it reads as 0s.