Introduction: Optics in Light-sculptures

About: After studying cinema at the Louis Lumière school, I worked as DP and assistant DP. In parallel to this work, I deepen research into light through sculpture and installations, whose common theme is the movemen…

Hello, my name is Julien Hogert. I graduate from the “Louis Lumière” cinema school a few years ago, where I studied, among other things, photography and a lot of optics. Now, I work in cinema, but I also make sculptures with lights. For the past 3 years, I have been making this series of little machines with leds, lens, prisms, mirrors, that transform the light analogically, to make abstract projections.

In this instructable, I will show you an ensemble of 4 machines, which, once assembled together, make this light-projection. These sculptures are for me a way to give the feeling that light is something alive. The works are conceived as sensible and contemplative experiences. The spectator con observe these analogical and mechanical machines, or watch the magical projections they generate - an immersion into an abstract experience of light, color and movement.

Rather than to explain all the steps of the construction of the machines, I will focus on the principles of optics that I use, explaining how they works and trying to share a little bit of my universe.

Step 1: The Light-sculptures

Step 2: About the Materials

Anyway, here is some information about the materials used. I found these after researching different options. The following are therefore some of my personal tricks. For all the mechanical parts: I use old-school “meccano” parts (for the wheels) and an amazing swedish kit named “FAC-System”. I found it on the famous French second-hand site: leboncoin. I was very lucky to find it, because it is not easy to come by! The motors are the very convenient 12v - 3 RPM: they have a 3mm thread, are quite small, and very cheap.

For the optical parts: The lenses I use are in acrylic. I can find them easily on ebay, they are the ones used with 10w leds. For the leds, I use the “high power Cree XQ-E” because the footprint is very small. The led drivers are cheap 1w/3w ones found on ebay. The dichroic cubes are easy to find, also on ebay. All the modules are made in Oak wood.

Step 3: The First Module: It All Begins With the Coma

The first module is quite simple. It has one led, an acrylic lens, and a motor that makes the lens oscillate. The aim of this first machine is to exploit an optical aberration : the Coma.

In optics, the coma is caused by the imperfection of the lenses. If the light rays of a led, are coming from the middle of the lens, the projection is a circle, but if the light rays are coming from the side of the lens, it will transform the round light into a kind of comet (that’s why this aberration is names the “coma”). This first module projects a circle of light that will transform itself into a kind of comet at the moment the lens will have a wider angle. To make the light transformations sensitive, you usually need to make it move very slowly and smoothly. That’s why I used a very slow 12v motor of 3 rotations per minute, slowed by the wheels (the motor spins a little wheel, that in turn spins a bigger wheel with a belt) and a potentiometer to adjust the speed. The oscillation of the lens is made with a connecting rod on the big wheel. The position of the led has to be adjustable to change the focus and adjust the effect. Last trick : If you want a beautiful and precise shape, you need a very punctual light.

And so we have a beautiful coma, moving slowly from one side to the other.

Step 4: Video : the "coma"

Step 5: Let’s Cut Our Circle Into Pieces

We now have a very slow and simple movement of light. To make it more complex and also to make aleatory, making shapes appear, metamorphose; we are going to cut the “coma” into pieces. For this I added one simple module : a line of a dozen plastic mirrors positioned vertically. When the coma passes through the mirrors it will get cut into pieces, and its trajectories will divert and reappear in a different place. Also, the fact that the mirrors are placed in parallel generate another good effect: the shapes will multiply.

The fact that they are plastic mirrors instead of normal ones is also important Since the surface of the plastic mirror is not flat, it adds some distortions as well as making the light movement random.

Step 6: Video : "Coma" and Mirrors

Step 7: Let’s Add Some Color Metamorphosis

Our living lights are quite good, they appear and disappear in an unpredictable way, but sometimes, the movement of our first module becomes too predictable. Maybe we can enrich our colony with some species to add different colours and behaviors.

To introduce different rhythms and to change the color in the process, I used dichroic cubes. This cubes are a combination of 4 prisms with selective colors. They are used inside video-projectors to make the color synthesis of the 3 axes of Red-Greeen–blue that create an unique image in color. So the cube acts as a reflecting mirror, with only one color of the light-spectrum. If we then put this cube onto a motor, it will alternate the color and add light movement due to the moving reflections. To put the cube at the middle of the lightpath between the lens and the mirrors I needed to create a kind of extension arm. That’s why these machines have a special mechanism designed to rotate the cube outside of its module.
You can find these cubes in all sizes. The bigger the cube, the bigger the color reflection. I made this module with a very big one, and added a led, resulting in a background color.

Step 8: Conclusion

Here you can see the resulting projection of the 4 modules combined.
I hope you enjoyed this dive into my universe. If you have any questions, I’m here to answer them!

Optics Contest

Second Prize in the
Optics Contest