at the heart. Visions arise, like lights, light-rays, rainbows, the sunlight and moonlight at dawn, the sun, the moon, and then the appearances of deities and forms. In this way the myriads of worlds are purified.Gampopa's Closely Stringed Pearls explains that this practice is to be done while falling asleep by initially setting an intention to "seize the radiance" (’od gsal zin par bya). Then the yogi visualizes five syllables in the heart-cakra. As sleep sets in, the yogi slowly shifts their attention from one syllable to the other. If one is successful in capturing the radiance or luminosity, a syllable Hum (ཧཱུྃ) will appear vividly in the heart, radiating powerful light and one will experience blissful sleep (and not the dream state, if one dreams, one has failed to capture the radiance). After waking up, it will appear as if one is in a strong glow. Gelug presentation In Tsongkhapa's exposition, there are various types of radiance or clear light. One is found in Mahayana sutras and in tantras, but there is an extraordinary radiance which is unique to tantra. The extraordinary radiance exclusive to highest yoga tantra is reached through inner heat practice and illusory body yoga joined with meditation on emptiness. This radiance, also termed "primordial wisdom of ecstasy and emptiness," is the focus of the system of six dharmas. Mullin (2005), p. 82. Tsongkhapa divides the practice of radiance into waking and sleep practices. The practice of radiance in the waking state involves visualizing oneself as the deity in sexual union and meditating on a blue HUM at the heart chakra which emanates light in all directions that purifies the universe. One dissolves the world into light and into oneself as the deity, then one dissolves into the mantric syllable HUM in one's heart chakra. The HUM then melts into light from the bottom up and one focuses the mind on the heart chakra. Then one practices collecting the vital winds into the central channel with the tummo method explained previously, which melts the drops, leading to the four blisses and the four emptinesses. One then experiences the dissolution of the elements and corresponding visions (see below), and then the radiance arises. One then joins the mind of radiance with meditation on emptiness. Gyalwa Wensapa, in his A Source of Every Realization, outlines how one practices generation stage and then tummo to generate the radiance yoga.