Reflectors and the Cat's Eye

 I'm sure you have taken pictures of family members or friends and seen a red "glow" in the center of their eyes -- or seen a night jogger wearing shiny reflective material for visibility purposes and wondered how each worked? It was not until I truly explored each of these simple facts and found that they were not only related, but much more complex and vital to other areas of science and of our daily lives then I would have ever thought! Naturally, this heightened my interest and decided to test them even further. What made this project even better was that it was not so mething which had a specific recipe or instruction guide, it was a unique project which had limitless boundaries to test!

So, what is this project truly testing?

So, you are probably wondering right now, what is this project all about? Basically, this project focuses on optical devices that have the property of returning light to a known source. In order to demonstrate the path of light, I simulated a cat's cornea lens and Scotchlite 3M, a shiny silvery reflective surface often used for night vision, to test reflection of light in hopes to determine the cause of red-eye and to explain the unusual irridescent glow of reflective paper.

What is a Cat's Eye and what does it have to do with reflection?

All eyes reflect light because our eyes reflect light in two directions, through the rods and through the cones. The cat's eye is of particular fascination because their eyes have a special reflective surface called the tapetum which improves their night vision by doubling the amount of light that is able to hit the retinal cells. This permits their eyes to remove diffused light inside the cell by propelling it back the opposite direction through the pupil in order to improve night vision -- so that's why cat's can see so well!! This special layer makes a cat's eyes glow brightly in the dark, especially when you shine a light ne ar their eyes at night.

Our eyes also have a similar property as cats, except this is where the infamous "red-eye" comes in. "Red-eye" is commonly seen after a flash photograph is taken. Our eyes tend to reflect the light from the flash back towards the camera which causes a reflection hence, red-eye. In order to minimize "red-eye", we need to move the camera lens much further away from our eyes [from the flash actually] in order to prevent the camera from "seeing" the light that eyes are beaming back at it.

The Cat's Eye Experiment!

In order to test the reflection concept of "cat's eye" I had to investigate much further into the physics (scary!) of reflection.

Setup
  1. First, I took a crystal ball (no not to tell fortunes) and placed it upon a black double-sided disc for support.
  2. Secondly, I took a piece of transparent film, orange, and a white piece of paper and held them together. I then took a flashlight and shined it upon the crystal in order to get an appropriate focal length. The focal length is the distance where the light enters the ball and comes to a point which is clear and in fact, focused. The distance for this experiment was approximately 1 cm.
  3. Lastly, I took a picture of the apparatus and it revealed an amazing discovery!
    The ball illuminated with red light and had a bright white light in the center.

What did this determine?

 When the focal length was focused and precise, I obtained no red-eye. However, I used the same setup and changed the focal length about 2 mm and saw red eye! I came to the conclusion that when the focal length from the camera's flash to our eye is not precise you will have the red eye effect otherwise, you can expect clear images without red-eye!! Truly Amazing!

Here is the image with the incorrect focal length. It is blurry and almost completely red!

What about reflectors??

 After discovering the amazing causes of red-eye, I thought my experimentation was done, however, Dr. Noe showed me a piece of paper which appeared ordinary only to the untrained eye and at t he wrong angle. Alas, I never thought a simple piece of grey paper could have so many amazing properties and uses! The paper he gave me was not paper but a reflective material called Scotchlite 3M which is commonly used on road signs, bicycles, and even on firefighter's jackets, to permit o bservation in the dark. When it was held at a certain angle at the light, it appeared to become illuminated with a white glow. So, I decided to investigate its reflective properties a bit further. For this particular experiment, I used Sprint Marketing Film, but for this experiment, I will use the name Scotchlite 3M because of its similar properties.

Scotchlite 3M Experiment! Let's see how far it glows!

 My main objective here was to discover how far Scotchlite 3M would glow and the setup was as easy as taking a picture. My hypothesis was, the further the distance, the greater the glow.

Look below for pictures of my experiment...

I took pictures of Scotchlite 3M from different distances.

I took pictures of Scotchlite 3M from 40 feet, 68 feet and 180 feet, respectively.
Look how bright the material is!

As I moved further away, the illuminescence intensified greatly. At one point it looked as the 3M was the only light source in feet!

I wondered what exactly caused such an effective source of reflection and such an effective illuminescence...I investigated further.

What is Scotchlite 3M Made from?

The remarkable thing about scotchlite 3M is that it is made up of tiny glass beads. These tiny glass beads are around 500 microns small and are sprayed on top of a painted surface such as, road signs and reflective tape! These beads have a carefully chosen refractive index (how much light will bend when entering) so that as the light shines through them, it will refract and then reflect inside of the glass beads. When this happens, most of the light will become reflected directly at the source from whence it came from causing a [bright] GLOW!

The challenge of making this perfect reflective material came back in 1937 when the company 3M thought it would be a profitable idea for a company to create a more reflective material then white or yellow paint. They decided to move onward with the experimentation and from this, they decides to sprinkle tiny glass beads onto a painted stripe in hopes to achieve a greater reflectivity. Although it was successful, they moved on to better experiments.

The idea of using 3M's roofing granules was suggested and a researcher named Harry Heltzer was determined to find the most reflective material of all time. So, he took reflective beads, 0.015 inch, about 100 microns, in diameter and proceeded to make his own reflective striping. By late summer, after all of his testing, he had an effective prototype: "a prefabricated, double-coated cloth tape with beads on one side." However, this could not stand up to inclement weather so the experimentation continued.

After the immense amount of experimentation, the glass beads were shifted from a horizontal striping to a vertical sign coverage. The result was astounding! The first Scotchlite 3M reflective sheeting was made and went on to become the leader in highway signage! See what persistence and determination can do!!!

Some Interesting Links...

Here are some cool links that Dr. Noe found...its remarkable how many uses Scotchlite 3M has!

LAEGOS Experiment! Very Interesting!
Reflectors on the Moon!
Bicycle Reflectors!
Pretty Cool Site on Reflectors!
See the Glowing in Action!

Let's tie it all together!

From my experimentation, I have found that the cat's eye acts like reflective material in many ways. When light moves through the eye, just as in glass beads, if the focal length is not precise, you will achieve a blurry image or "red-eye." Similarly, if the light from a source hits the reflective tape at an improper length, you will not be able to see the reflective glow instead, it will appear grey.

So, light has many functions in our everyday lives! It was fascinating to discover that light and physics could be fun and how important it is to everyday life! I want to thank Dr. Noe for making this experience possible and for all of his time and patience.

References:

Research by: Kristin Regan

Advising Professor: Dr. Noe

Special Thanks to : The Laser Center and the W.I.S.E. Program

Any further questions? I'll be happy to answer :)

Email Kristin })i({