Corner Cube or Retro Reflectors These Corner Cube or Retro Reflectors are resource material to...

Corner Cube or Retro Reflectors

These Corner Cube or Retro Reflectors are resource material to support parts of

STAO’s ScienceWorks Grade 10 Optics

The following are excerpts fromL4 The Laws of Reflection (Slides 34 to 57 of 74)

Corner Cube or Retro Reflectors

When light is shone on them from something like a car (Incident rays) it is reflected straight back toward the car. The Reflected rays are parallel and in the opposite direction of Incident rays.

Corner Cube Reflectors,are used in Bicycle Reflectors

Bicycle Reflectors

Why not just use a mirror to reflect light back into the Eye/Brain?

Bicycle Reflectors

Bicycle Reflectors

Slight changes in the mirrors orientation would cause the reflected light to miss the Eye/Brain?

Bicycle Reflectors

If two mirrors are arranged at 90º, slight changes in the mirrors orientation do not affect the direction of the reflected light.

Bicycle Reflectors - Mathematical Proof

1) Use the laws of reflection and geometry to prove light is reflected back, parallel to the incident ray from two mirrors at right angles?

At B, let the first Angle of Incidence = Angle of Reflection = x or (i = r = x)


At C, let the second Angle of Incidence = Angle of Reflection = y or (i = r = y)


Note A= 90ºIn ∆ABC, A+x+y = 180 º90º+x+y = 180 º x+y = 90 º

The Transversal line BC2x+2y = 2(x+y)

= 2(90º) = 180º

Lines IB and CR are parallel because the interior angles on the same side of the transversal are supplementary


This proof is only in two dimensions.


In two dimensions, this only proves that the Incident and Reflected rays are on parallel planes (yellow).

The rays could be drawn on planes (yellow) perpendicular to (in & out of) the page.

All light is reflected in horizontal planes. No light is lost to up and down reflections

Looking from above, the two mirrors act like a single mirror as far as the horizontal direction of the reflected ray is concerned.


Slight changes in the two mirrors horizontal orientation would cause the reflected light to miss the Eye/Brain?


But All light is reflected in a horizontal plane.

No light is lost to vertical reflections so all Eye/Brains see bright reflected light.


If three mirrors are arranged like the corner of a cube,they are called “corner cube reflector”or a “retro reflector”. They are all at right angles to each other,

In corner cube reflectors,the Incident ray and final Reflected ray are parallel lines. They are in exactly opposite directions.

But the light must reflect form each of the three mirrors

Measuring the Distance to the Moon

Laser ranging Corner Cube Reflectors were positioned on the Moon in 1969 by the Apollo 11 astronauts.

Laser pulses beamed at the reflectors from Earth, help scientists determine the distance between the earth and Moon to an accuracy of about 3 centimeters.

Precut Corner Cube Reflector mirrors are available at STAO Store. The following shows how to finish assembling them.

All mirrors will last a very long time if the back is covered with duct tape. BUT Be careful you do not damage the coating on the back by trying to remove or adjust duct tape.

You can often obtain scrap glass mirrors from Window & Mirror companies at reasonable prices.

Seeing Things Making Corner Cube or Retro Reflectors


The Precut Corner Cube Reflector mirrors are shipped flat in order to reduce shipping costs.

They look like the above picture


Fold the top two corners together as shown in the next series of slides


Flip over and


Flip over and duct tape the back


Trim the access duct tape from the back


If you have extra small square mirrors you can also make your own corner cube reflector.If possible use triangular mirrors.


Dust tape the first two mirrors at 90°.


Place the next mirror on top


Place the next mirrors on top and duct tape


Flip over


This is the corner cube reflector


This is the corner cube reflector that is nearly identical to purchased ones

The area outside the dotted lines can cause confusion as the light ray must reflect from all mirrors if it is to reflect directly back at the origin of the incident ray.

Bicycle reflectors use this shape to reflect light back light ray must reflect from all mirrors if it is to reflect directly back at the incident ray

Bicycle Reflectorsand the Distance to the Moon

In other words, Check it out! Does the theory work?Arrange three mirrors so they form the corner of a cube. Then shine a laser pointer at them and see if it’s reflected back regardless of the direction you shine the laser. Misting with a spray bottle will make the laser beam visible. Try a Bicycle Reflector

It is certainly true that principles cannot be more securely founded than on experience and consciously clear thinking.— Albert Einstein

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