Heiligenschein (or "Holy Light") is an everyday optical effect that anyone can see best on a sunny morning (or evening) on dew-covered grass. Simply turn so you're looking directly at the shadow of your head on the dewy grass (that's called the "anti-solar point", i.e., the point that is directly opposite the sun along the line formed by the sun and your head, particularly your eyes) and if you look closely at the shadow of your head you will see a solid circle of white light around it, like a halo. That's heiligenschein. Here's an example of it:
Heiligenschein (or "holy light") surrounding the shadow of the photographer's head on a dewy morning.
Now heiligenschein is related to the optical effects of halos and glories, although a technical difference is that halos and glories are rings of light usually with bands of colors, and heiligenschein is a solid circle of white light. Importantly heiligenschein can only be seen by a person observing their own shadow. You cannot see the heiligenschein on another person's shadow, nor they yours (unless they are very close to your head, like peeking closely over your shoulder)—heiligenschein can only be seen at each person's own anti-solar point (which is unique to each person). Now follow me below the orange fleur-de-lis for a little bit more about this interesting everyday optical effect, and the metaphor I'll make later with it about the hubris of the mighty.
Heiligenschein is the optical effect of retro-reflection of light from a solid clear spherical (or nearly-spherical) object attached to a background material. The effect shown above is one example (which is more precisely called "dew heiligenschein") which is caused by the retro-reflection of the sun from the small nearly spherical dewdrops on the blades of grass. This same effect is also produced by the small glass spheres used on the reflective surfaces of traffic signs to make them shine back brightly at you when your headlights are on. And it is also why dog's and cat's eyes glow brightly straight back at you in the dark when you shine a flashlight face-on at them, as well as being the effect that produces the "red-eye" that you sometimes get when taking a flash photograph of someone.
Here is a simple light ray diagram of this effect:
Light ray diagram illustrating the optical effect of heiligenschein.
Light is focused by the eye or sphere to the point shown, but by the laws of optics light from that focused spot can also travel out of the eye or sphere by exactly the same path
. That is, some of the light (because the rest of the light is absorbed) can emerge along exactly the same path from the eye or sphere that it took to enter the eye or sphere. That is retro-reflection. It's different than reflection from a mirror in that if the mirror is tilted the light reflects in a different direction than it enters, but not with retro-reflection or heiligenschein. In heiligenschein, light exits the sphere along the same path that it entered it.
Since the "red-eye" effect in photography is related to heiligenschein and the retro-reflection of light from the eyeball, many photographers know that one way to reduce "red-eye" is to move the flash further away from the lens. The red-eye light from the eye is retro-reflecting back to the source of the light, i.e., the flash, not the lens! And since the effect is limited in angular size, if you can move the flash far enough from the lens, the lens won't see the reflected "red-eye" that is actually going toward the flash.
Also with heiligenschein since reflection is the main action occurring the light observed is white as there is also little optical dispersion going on so you don't see the spread of colors as they would occur with a prism or grating, or as you see in rainbows, glories, or halos. Also because of the retro-reflection, the circle of light is solidly filled, like the sun itself (at least the part not obscured by your head's shadow), and is not a ring. And because of the variability in the not-quite-spherical shapes of the dewdrops there is also some spread in the angular size of heiligenschein so that it extends for some small distance around your head (giving it its extended "halo-like" effect).
Now the image below is one of the related example of a "glory" which is the colored ring around the shadow of an airplane on a lower-lying cloud layer—note that it does appear similar to and occurs at the same anti-solar point, but is not identical to, heiligenschein:
Example of a "glory" around the shadow of an airplane on a lower-lying cloud layer.
Much of the information I mention here about heiligenschein (and about rainbows, halos, and glories) was from Robert Greenler's "Rainbows, Halos, and Glories" (now out of print)
, which is an excellent general introduction to these optical phenomena, with lots of photos and explanatory diagrams as you would expect for such a visually oriented subject.
Finally, the long awaited metaphor of heiligenschein to the hubris of the mighty. The most important point of this metaphor is that each person can only see his own heiligenschein, or holy light, and not anyone else's. And every other person can only see their own "holy light", but not yours. Therefore, in an example I'll relate from Greenler's book of one case of the mighty and powerful and ego-mad of the past (and metaphorically today also) who literally think that when they see their actual own "holy light" in the sunlit morning grass (but not anyone else's), they think that God has selected them for greatness and for dominion over others. In particular, Greenler uses the example of Benvenuto Cellini, an Italian sculptor from the 1500s with a huge ego, strong religious feelings, and prone to fatal duels with those who disagree with him. When Cellini discovers heiligenschein about his head in the sunlit morning dew (and no one else's) and sees that halo, which is so like that of the saints in the paintings of that era, well, you can guess the consequences. Here's Cellini's description of what we now call heiligenschein from his own Autobiography of Benvenuto Cellini:
I will not omit to relate another circumstance also; which is perhaps the most remarkable which has ever happened to any one. I do so in order to justify the divinity of God and of His secrets, who deigned to grant me that great favor; for ever since the time of my strange vision until now an aureole of glory (marvellous to relate) has rested on my head. This is visible to every sort of men to whom I have chosen to point it out; but those have been very few. This halo can be observed above my shadow in the morning from the rising of the sun for about two hours, and far better when the grass is drenched with dew. It is also visible at evening about sunset. I became aware of it in France at Paris; for the air in those parts is so much freer from mist that one can see it there far better manifested than in Italy, mists being far more frequent among us. However, I am always able to see it and to show it to others, but not so well as in the country I have mentioned.
Greenler's commentary about this is to the point:
I would say that Cellini gives a rather good description of the heiligenschein. The only part that seems questionable is his statement that the light around his head could also be seen by those favored few men to whom he chose to point it out. But given a style of life that involved fatal duels over personal disagreements, such a statement is probably understandable.
Of course, we now understand the scientific and optical underpinnings of this effect of heiligenschein. So the appeal to the "divinity of God and of His secrets" is no longer necessary because our present scientific understanding of this particular behavior of light serves to explain it completely.
But the larger metaphor still holds: That just because you can see the holy light about you, but not about others, does not necessarily make you special and one of the chosen. And if you truly believe that the holy light makes you one of the chosen, then that is the very definition of hubris and eventually you will be brought down low. You have forgotten the fact, and the consequences, that every last one of us can see our own holy light—and that often we don't realize that this is true simply because we can't see it in others. We need to realize that everyone possesses their own holy light—and we should treat each other as such.
So please go out some sunlit dewy morning and view your heiligenschein, and appreciate your holy light—and that of everyone else. Realize that that holy light is yours and yours alone—but that that is also true of everyone else and their holy lights, even if you can't see it around them.