Also known as Cellini's halo, after the Italian artist Benvenuto Cellini (1500-1571). Heiligenschein is German for saint's light or holy light. The term is used to denote a "physical illusion consisting of a bright, colourless, or faintly coloured glow that can be seen around the shadow of one's head when looking at bedewed grass at the antisolar point (i.e. a point in the landscape opposite the Sun) while the Sun is at a low elevation angle. Sometimes a surface other than grassland can produce heiligenschein as well, but dewy grass is the medium best known for this effect. The mediation of heiligenschein is attributed to the retro-reflection of sunlight by the dew drops on the grass, as well as the blades of grass themselves. A related phenomenon which occurs while viewing one's shadow cast on smooth water is called the aureole effect. Neither phenomenon should be confused with "Buddha's light or with the "Ulloa circle.
References
Lynch, D.K., Livingston, W. (1995). Color and light in nature. Cambridge: Cambridge University Press.
Minnaert, M. (1954). The nature of light & colour in the open air. New York, NY: Dover Publications.
Dictionary of Hallucinations. J.D. Blom. 2010.