The document discusses the phenomenon of heiligenschein or "holy light" seen around shadows cast on dew-covered grass. It explains that dew droplets act as lenses, focusing and backscattering sunlight to produce a bright halo around shadows. The document provides examples and photos of this effect and explains that it is caused by the refraction and reflection of light through spherical water droplets on grass leaves. It notes that the heiligenschein looks white because the individual points of scattered light saturate the eye's color receptors.

1. SCATTERING…
EXAMPLES…..
Y.RAJEEV.
OPTOMETRIST 16TH BATCH.
COLLEGE OF VISUAL SCIENCE.

4. In a simple manner…
On a morning time
A man standing near to a dew wetted grass area
His shadow is falling down on the dew wetted grass.
There is a bright white area around his shadow of head.
Then he is moving his camera away from the eye
Now that bright white area is around the shadow of
camera.

7. What is water dew???
Dew is a water in the form of droplets that appears on
thin,exposed objects in morning due to condensation.
As the exposed surface cools by radiating it’s heat
atmospheric moisture condenses at a rate greater than that at
which it can evaporate, resulting in the formation of water
droplets.

8. On a morning when shadows are long and the grass is dew
wetted, look at the shadow of your head.
With luck it will be enveloped by a sparkling white glow.
The glow is centered on the antisolar point and so, like the
glory, each has their own.
When I moved the camera from my eye out to arms
length, its heiligenschein moved with it.
This is the 'heiligenschein' or 'holy light'.

9. Heiligenschein is a bright spot of light around the shadow of
the observer's head, cast on dewy grass land.
The dew droplets on the grass act as lenses, focusing sunlight
on the grass leaves, strongly illuminating them, and working
again as a lens for the backscattered light.

11. This effect is enhanced by the fact that in the antisolar point (the
point opposite the sun, i.e. the shadow of one's head),
no other shadows are visible, and thus the region looks much
brighter because the light and dark details of the surface are
integrated by the eye.

12. Look for the Heiligenschein early in the morning, when the sun is
low and thus your shadow long, and move yourself to let the
shadow be cast on wet dewy grass.
The effect is very common, so you should be likely to see it.

14. •The heiligenschein does not need very small droplets
because it does not depend on diffraction.
• However, the drops must be small enough to hang on
leaves in a special way.

15. Spherical dew drops act as lenses and bring sunlight to a crude
focus ~20% of their diameter beyond their rear facing surface.
Some drops rest on the tips of small hairs and do not touch the leaf
surface.
When the drops and hairs have the right dimensions, sunlight is
focussed in a bright spot on the leaf.

16. •Light from the spot scatters in all directions but some returns
through the droplet along almost the same paths as it came.
•The net effect is that each drop 'backscatters' sunlight, returning
it most brightly in directions towards the sun.
Dew thus shines brightly at the antisolar point to form a
heiligenschein.
•But if the lawn or field is large enough check forty degrees away
from the antisolar point for the same droplets can also form a
speckled dewbow.

17. It is said to look white because the individual points of light
saturate the eye's colour receptors and to some extent cameras.
WHY IS THE HEILIGENSCHEIN NOT
GREEN???

18. A useful scientific model was proposed in
1874 by Lommel and is still the leading
explanation for the heiligenschein today.
Lommel noticed that the water droplet rests
on small hairs which separate it from the
leaf's surface.
The drop brings sunlight to a crude focus.
When this is at the leaf surface, some light is
scattered back through the drop to form the
heiligenschein.
I
N
P
A
S
T

21. •Molecules in the air scatter blue light from the sun more than
they scatter red light.
•When we look towards the sun at sunset, we see red and orange
colours because the blue light has been scattered out and away
from the line of sight.

22. DO IT YOURSELF –SUNSET
•With a few items from your kitchen, experiment with the real
reason why the various colors in the sky exist, and why the sky
turns red-gold at sunset and sunrise.
•This experiment replicates the scattering of small particles in
the earth’s atmosphere in a glass of water, using a little bit of
milk to scatter.
Ingredients
A clear glass pitcher or tall jar with straight sides
Milk (2% or Whole is best, or dry milk power)
Water
Flashlight

23. How to do it?
•Fill a glass pitcher with water.
•Add milk a little bit at a time, just until the water is murky and
translucent.
• (NOTE: if you use milk powder,
add a pinch at a time. If you
use skim milk, you’ll need
more than with 2% or whole.)

24. •Place the flashlight so that the beam shines through the glass.
View the light from the side of the pitcher (at a 90° angle from the
path of the beam).
•What color is the light? It should appear blue.
Look at the beam of light again, this time from the end of the pitcher
(at a 180° angle from the path of the flashlight).
•What color is it now? You will notice that this time, the light has a
red-orange hue!

25. How it works???
•In this experiment, the flashlight represents the sun.
•As you shine the flashlight, the light collides with and bounces off of
the many molecules from the milk (the protein and fat droplets),
which is analogous to the various gases and dust that comprise the
atmosphere.
•These molecules scatter the light, and the light waves with the
shortest wavelengths are scattered the most.
•Blue light is scattered ten times more than red light in all directions.

26. •The red light, having the longer wavelengths continues to travel
largely in its original direction.
•Therefore, the striking blue of the sky we see is the result of the
scattered blue light waves.
•In this experiment, it also means that we get the blue tinge when
looking at the light at an angle through the milky
water due to the light being scattered
by the protein and fat molecules.

27. WHY IT IS IMPORTANT TO US???
DOES SCATTERING ONLY TAKE
PART IN NATURE???
AS OPTROMETRIST ARE WE
DEPEND ON SCATTERING???

28. Scattering of light in the human eye
•Intraocular scattering has been known for some time to be an
important problem.
•Even for healthy eyes the scattering from a bright source can mask
the presence of accompanying objects.
.

29. • Scattering inside the eye can be increased
with age,
with disease,
e.g. cataracts or by cellular changes in the
membrane behind the lens,
or because of accident or surgery in the eye.

30. •Scattering can also be used to characterize the alignment of the rods
and cones in the retina of the eye.
•These problems have been studied or diagnosed by measuring the
backscattering of light which is designed to illuminate the eye.
•However, there has been little work on the effect of scattering on the
image detected by the person in the presence of scattering, and in
particular in the presence of two or more different sources of
scattering, e.g. a patient with cataracts who has also been operated
by LASIK

31. SCATTERING TAKE PLACE IN….
•WATER DEW
•COLOUR OF SKY
•COLOUR OF SEA
•CATERACT EYE
•COLOUR OF SETTING AND RISING
SUN