In terms of energy – there are three characteristic ways in which the energy manifests – Dang, Rolpa, and rTsal (gDang, rol pa, and rTsal). Dang is the energy in which ‘internal’ and ‘external’ are not divided from that which manifests. It is symbolised by the crystal sphere which becomes the colour of whatever it is placed upon. Rolpa is the energy which manifests internally as vision. It is symbolised by the mirror. The image of the reflection always appears as if it is inside the mirror. rTsal is externally manifested energy which radiates. It is symbolised by the refractive capacity of the faceted crystal. For a realised being, this energy is inseparable in its manifestation from the dimension of manifest reality. Dang, Rolpa, and rTsal are not divided.
Dang, Rolpa and rTsal are not divided and neither are the ku-sum (sKu gSum – the trikaya) the three spheres of being. Chö-ku (chos sKu – Dharmakaya), the sphere of unconditioned potentiality, is the creative space from which the essence of the elements arises as long-ku (longs sKu - Sambhogakaya) the sphere of intangible appearances – light and rays, non material forms only perceivable by those with visionary clarity. Trülku (sPrul sKu – Nirmanakaya), the sphere of realised manifestation, is the level of matter in apparently solid material forms. The primordial base manifests these three distinct yet indivisible modes. (Van Schaik, 2004)
http://en.wikipedia.org/wiki/Tulpa#Three_aspects_of_energy