 For playback of 4K content, the BDA introduced a variant of Blu-ray called Ultra HD Blu-ray.The information density of the DVD format was limited by the wavelength of the laser diodes used.Following protracted development, blue laser diodes operating at 405 nanometers became available on a production basis, allowing for development of a more-dense storage format that could hold higher-definition media, with prototype discs made with diodes at a slightly longer wavelength of 407 nanometers in October 1998.