Why is Blue-ray disc black on top?

The Blue-ray disc uses a blue (technically violet) laser operating at a wavelength of 405 nanometre (nm) to read and write data. Conventional DVDs and CDs use red and near infrared lasers, at 650 nm and 780 nm respectively. Because the Blu-ray disc data layer is closer to the surface of the disc, compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection. Now, the rewritable media are spin-coated with a scratch-resistant and antistatic coating, which gives the surface of the disc its black colour.