ge University Press) 2 (S234):  445–6, doi:10.1017/S1743921306003668, Bibcode: 2006IAUS..234..445K, "Planetary nebulae (PNs) have high dust content and radiate strongly in the infrared. For young PNs, the dust component accounts for ∼1/3 of the total energy output of the nebulae (Zhang & Kwok 1991). The typical color temperatures of PNs are between 100 and 200 K, and at λ >5 μm, dust begins to dominate over bound-free emission from the ionized component. Although PNs are traditionally discovered through examination of photographic plates or Hα surveys, PNs can also be identified in infrared surveys by searching for red objects with a rising spectrum between 4–10 μm." Liu, X.-W.; Storey, P. J.; Barlow, M. J.; Danziger, I. J.; Cohen, M.; Bryce, M. (March 2000), "NGC 6153: a super–metal–rich planetary nebula?", Monthly Notices of the Royal Astronomical Society 312 (3):  585–628, doi:10.1046/j.1365-8711.2000.03167.x, Bibcode: 2000MNRAS.312..585L Maciel, W. J.; Costa, R. D. D.; Idiart, T.