Animated Drawing on a Light Board #phablabs

Animate your drawing on a plexi plate! Programme the RGB LEDs in such a way that the wheels on your drawing are turning around or a plant is growing.

An extended version of this workshop includes the mounting and programming of the LED driver and the dedicated creative session to exploit the phenomenon of coloration by light absorption and fluorescence.

The workshop exist out of three parts:

1. Analyze the operation of light board: total internal reflection, role of rough edge, notion of optical contact.

2. Assemble the light board in two steps: assemble the Light guide support and the device.

3. Examine the colour content of various objects by illuminating with different bands of the visible spectrum (a special colour chart can be printed and examined using this experiment)

Properties of this workshop:

Timeplanning: Total: 2-3h

1. Understanding theoretical information such as 'total internal reflection', 'colour mixing' and the process of 'fluorescence': 45 minutes
2. Cutting of the light guide and the plexiglass: 30 minutes
3. Assembling the light board and drawing: 60 minutes
3. Playing with the light board: 45 minutes

Target audience: Young minds (10-14 years old) & students (15-18 years old)

Estimated cost: € 20

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This workshop has essentially two main photonics contents to introduce:

1. The first one is the principle of light guidance within a Plexiglas sheet
2. The second one is the science of color and the role of lighting on color perception.

LIGHT GUIDANCE IN A PLEXIGLAS PLATE

A light board is essentially a planar light guide coupled with LEDs, based on the same principle than edge-lit backlight of LCD flat panel display or than LED planar lighting. If you have the chance to demount a LED ceiling light (photo 1), you will see it consists out of different elements: LED ribbons, light guide and patterning for light extraction.

Guidance in Plexiglas plate is based on the principle of total internal reflection by refraction. Refraction is phenomenon that often occurs in nature. Photo 2 shows a turtle in water. The light beams coming from the turtle are reflected at the sea/air interface, this explains the double image of the turtle.

Total internal reflection is a particular case of reflection where light gets reflected inside a material over and over again. The phenomenon occurs when the angle of incidence is larger than a critical angle with respect to the normal to the surface. The expression of the critical angle can be found thanks to the Snell's law: n(1)sin(i1)=n(2)sin(i2)

The critical angle is the angle i1 for which i2 = pi/2. Hence, i1=arcsin(n2/n1). It depends on the optical index, and internal refraction is possible only when n2 < n1. Photo 3

In this workshop a plexiglas plate will be used, and the light will be trapped into the plate, as shown in photo 4. We do not see any light coming from the plate, but there is in fact light trapped inside. The light that can be seen is the light emitted by the LED in the observer direction, the light emerging at each rough edge of plate, and the light that escape from the plate due to defect at its surface (such as the one induced by the fingers). This phenomena is called the "Frustrated total internal reflection", and it is also what happens when we draw or write on the light guide surface.

It is important to introduce the concept of a clean, polished interface (fundamental for optical devices) where the law of refraction applies, compared to rough interface, where the light is essentially scattered, as illustrated in photo 5,6 & 7.

In other words, as the edge of the light guide is not polished, the following popular experiment using laser (photo 8) cannot be reproduced.

The rough edge of the Plexiglas can be improved:

·By polishing
·By pasting an aluminum foil (even if the obtained improvement in term of light trapped in the light guide can hardly be seen at eye, and would require more accurate illuminance measurements)

Interestingly, a white painting of the light guide edge would not change anything (at eye). Indeed, white painting is also a source of light scattering, as rough interfaces.

Similarly, the light coupling between LED and light guide can be improved:

·By introducing an optical paste (not recommended in the workshop because of the potential degradation of the paste induced by LED heating);
·By adding prism to the light guide, to capture a larger fraction of the light emitted by the LED and guide it into the plexiglas sheet;
·By inserting the LED directly into the plexiglas.

OPTICAL CONTACT BETWEEN THE LIGHT GUIDE AND A TRANSPARENT SURFACE

It is also possible to draw on a transparent slide and place it on the plexiglas surface (as seen in photo 9: the dragon on the left was drawn directly on the plexi plate, the dragon on the right was drawn on a transparent slide placed on the plexiglas surface.). However, in this later case, we need to put the two elements in optical contact, i.e. to avoid a prejudicial air gap between the plexiglas and the slide. This can be done by introducing a liquid with a similar optical index between the plexiglas and the slide. Water works.

Try out another interesting experiment with a simple adhesive tape. If we put an adhesive tape directly on the plexiglas surface, it does not change its aspect, as there is almost no optical contact between the two elements. However, it is possible to let the light escape by applying a local pressure. This procedure allow to write with light on the adhesive tape, as shown in photo 10-15).

Interestingly, if the adhesive tape is removed, the optical contact of course disappears, and the written message is erased.

Photo 10: Two slices of adhesive tape on the plexiglas light guide surface.
Photo 11: Writing on the tape by applying a pressure.
Photo 12: Result of writing.
Photo 13: Erasing the writing by removing the tape.
Photo 14: Putting back the second tape ribbon.
Photo 15: Writing again.

Daylight contains the full visible spectrum, and thus can reveal all colors. However, the combination of only red, blue and green light, called primaries colors, can also produce white light. White light (or white color) is thus not unique, and can be obtained by an infinite combination of light, providing that the full spectrum is covered.

The color of a surface (induced by inks and pigments coloration for instance) is not a fundamental properties of the surface itself, but also depends on the lighting. Each colored surface is in fact absorbing a fraction of the light depending on its spectrum. As illustrated on Photo 1, a red surface appears red because it is absorbing all the spectrum, except red. However, a red surface illuminated by blue or green light will appear black (absence of light), as blue or green light are absorbed by red surfaces. A white surface essentially absorb no visible light.

Two colors are said to be complementary colors if their mixing is white (see photo 2). Complementary colors of primaries color are respectively cyan (blue + green), magenta (red + blue) and yellow (green + red). Interestingly, complementary colors appears black when illuminated by only one primary color. For instance, as cyan is made of blue and green inks, it turns black only under red light.

These concepts can be nicely illustrated by drawing on the light board (see photo 3). We recommend to use acrylic painting, as it can be easily washed used soap and water. It is an illustration of complementary colors cyan, magenta, yellow under red, green and blue light. Note that the theory is not perfectly respected as magenta is also partially dark under blue light, and yellow not completely green under green light. This is probably due to the use of fluorescent elements in magenta and yellow inks.

FLUORESCENCE

Contrary to most material that only absorb part of the incident light spectrum, fluorescent material not only absorb light, but also re-emit light with a different spectrum, usually at a short wavelength (lower photon energy). Under excitation, fluorescent material appears glowly, because the light emitted by the fluorescent material is not expected by the human visual system and is interpreted as an excess of light.

Photo 4: Typical spectrum of absorbance and fluorescence of a fluorescent material.

Each fluorescent material needs a specific light excitation spectrum. It is the UV light in many case, which is quite spectacular, as UV light is not visible. However, we avoid to use any UV light during our workshop, as UV light might damage human retina.

As shown in photo 5, all fluorescent inks used in classical pencils are fluorescent under blue light, and some of them (pink and orange) are also partially fluorescent under green light. It is typically difficult to discriminate the absorption and fluorescent contribution of inks and painting from an experimental point of view, this issue is addressed in our third workshop (for young professional). Fluorescent inks are attractive for drawing on the light board as they appears colored under blue light (and sometimes green light), contrary to classical absorbing inks (which are dark or blue only).

Simple version: Static drawing

Photonics parts:

*12V LED ribbon with RGB lights

Other parts:

*Plywood: 3mm thick
*Plexiplate: 5mm thick
*LED ribbon RGB driver and 12V power supply
*Fluorescent stabilos
*Acrylic pencils
*White paper and pen
*Ruler
*Sandpaper
*Wood glue or hot glue gun
*Painter's tape

Tools (for example in Fab Labs):

*Laser cutter or circular saw
*Soldering iron and tin

Advanced version: Animated drawing

Photonics parts:

*LED ribbon with RGB lights

Other parts:

*Plywood: 3mm thick
*Plexiplate: 5mm thick
*Arduino nano
*Circuit PCB - file attached
*Resistor 220 Ohm
*2x resistor 80 Ohm
*3x loader LCC 100nf
*Axial loader 100nf
*Rotary encoder EC12PLRVFD24
*Fluorescent stabilos
*Acrylic pencils
*White paper and pen
*Ruler
*Sandpaper
*Wood glue or hot glue gun
*Painter's tape

Tools (for example in Fab Labs):

*Laser cutter
*3D printer
*Soldering iron and tin

The LED ribbon contains circular spots composed of 3 LEDs that we can separately controlled (one red, one green and one blue). Thanks to the control unit we can obtains 7 different lighting: red, green, blue, magenta (red+blue), cyan (blue+green), yellow (red+green), white (red+green+blue). Photo 1

Don't find the material you are looking for? Via this link you could buy all the photonics material needed for this workshop. http://b-photonics.eu/photonics-toolkit/general-p...

Cutting of the plexiglas plate

Photo 1: First, trace the cutting lines on the plate with a pen and don't remove the protective film that is on the plate. Cut the plate into a 10 x 15cm rectangle.

Use a lasercutter to do this. If you don't have a lasercutter, you can also opt for a circular saw in order to cut all the rectangles without removing the protection film of the plate, and don’t forget to hold the plate tightly. (Photo 2)

Use the sandpaper on each side of the plate to remove all of the smudge. The final plexiglas plate looks like photo 3.

Laser cutting of the Light guide support

Simple version: Static drawing

Photo 4: Use the file attached to cut the light guide support. (Light guide dxf).
Photo 5: Remove carefully all of the parts.
Photo 6,7: With the wood glue, stick the different parts together as shown on the photos.

Advanced version: Animated drawing

Photo 8: Since the advanced version is making use of an arduino nano, the light guide support has a slightly different design. Cut out the box with a lasercutter with the animated drawing.dxf attached.
Photo 9: Glue together the side of the box with the back.
Photo 10: Place the system inside the box.
Photo 11: Don’t glue the top on the box because otherwise you can’t access the system if something go wrong.

Simple version: Static drawing

Solder the LED ribbons with the electric wire, then use the heat-shrinkable sleeve to protect the soldering. Connect the RGB LED ribbons to the driver and to the power supply. (Photo 1&2)

Advanced version: Animated drawing

This advanced version is making use of a custom designed PCB. We share the design files with you, so you could make it, or let it be made. (You can find the file in the part list step)

Photo 3: Take all the components you need.
Photo 4,5: First place the resistors and solder these on the PCB.
Photo 6: Cut off the legs, but don't throw them away. We are going to re-use them later.
Photo 7: Place the loader and the axial loader on the circuit and solder them on the PCB.
Photo 8: Fold the axial loader. It is going to make the device flatter.
Photo 9: Take the legs you've cut off and fold them as shown in the photo.
Photo 10: Cut a piece of the Led ribbons, so it fits on the circuit. Solder it to your circuit with your folded legs.
Photo 11: Solder the rotary controller and the Arduino nano on the PCB. Don’t forget to place the USB output to the outside of the circuit.

Download the Arduino IDE program (C language) on your computer. (See file attached) Then, connect the Arduino to your computer, launch the Arduino IDE and copy the code FluoBoard.ino. Save and quit.

Now you can connect your device, turn it on by pressing on the rotary device and try all the built in modes. You can design your own mode by modifying the C program that drive the LEDs. This point is interesting for the next step, as each new images will require a specific modification of the LED driver.

The final LED driver, based on Arduino, using an USB plug. In photo 1, we can see that each LED can be controlled independently.

Simple version: Static drawing

Before you draw on the plexiglas, try it first on paper. That is also easier to then transfer the model on the plexiglas. Play with different colours, so some parts of your drawing will light up with different colours of the LEDs.

Photo 1-3: For example with the dragons: The red part of the dragon appears on red light and disappear on blue light.

Photo 4,5: Second example: Application of the principles of fluorescence: a hidden word, "cat", is written using a fluorescent ink. It is best revealed in this case using magenta lighting.

An another sympathic method for the drawing is to use google to find pictures. Then dispose the Plexiglas plate on a screen and calk the picture.

Advanced version: Animated drawing

Light guides can be used in several different ways to get creative, funny and amazing images. In the following, we show 4 different ways to use light guide :

- Reveal part of the drawing playing with lighting (example 1: the dragon) See photo 1-3
- Create animated images (example 2: the bike & example 3: the flower)
- Hide message within the drawing (example 4: the hidden cats) See photo 4,5

Example 2: The bike in motion. This is an application of the concept of complementary colors. The radius of the bike's wheels are made of complementary colors cyan, magenta and yellow. Using alternatice red, green and blue lighting, radius turns black one after the other, giving a feeling of motion. photo 6-9

Example 3: The flower is an application of the principles of fluorescence. The flower stalk is made of fluorescent pink that appear both on green and blue light, while the flower petal appears only with the blue light. photo 10-13

There is surely other ideas in the air (other suggestions: exploiting both side of the light guide, 3D images with anaglyphs …). Please let us know all the new ideas that will come out of your works !

We suggest to start with samples showing the appearance of each inks available in the fablab under different lighting (primaries and complementary colors). Then, we can present our examples, and asks students to create other drawing !

ABOUT PHABLABS 4.0 EUROPEAN PROJECT

PHABLABS 4.0 is a European project where two major trends are combined into one powerful and ambitious innovation pathway for digitization of European industry: On the one hand the growing awareness of photonics as an important innovation driver and a key enabling technology towards a better society, and on the other hand the exploding network of vibrant Fab Labs where next-generation practical skills-based learning using KETs is core but where photonics is currently lacking. www.PHABLABS.eu

This workshop was set up by the Institut d'Optique Graduate SChool and University Jean Monnet de Saint-Etienne in close collaboration with Openfactory.