In Tsongkhapa's system, it is necessary to become acquainted with the tummo, radiance/clear light and illusory body practices before practicing dream yoga (which he sees as an extension of illusory body yoga). According to Tsongkhapa, before practicing dream yoga, one must first master the yoga of retaining the radiance/clear light that arises at the moment of falling asleep (through experiencing the visions etc.) as explained above. If one practices this before sleep, when a dream occurs, one will realize that one is in a dream.