Retinal persistence, the secret of holographic fans

wall of holographic fans displaying a shoe

Retinal persistence and holograms

There are plenty of ways to create an hologram. From Pepper’s ghost to security holograms, holographic technology offers many possibilities that we would like to share with you. We have already written an article about “Pepper’s ghost” holograms but here, we are going to dwell on the notion of retinal persistence and on its link with holograms.

The human eye may be fascinatingly complex, but it is not infallible. There are a lot of optical illusions and thanks to them, we can create holograms. Our holographic fans use the retinal persistence to display 3D images for instance.

Retina drawing

What is retinal persistence

In reality, retinal persistence is an optical phenomenon that creates persistent images that the retina cells keep in their memory during approximately 1/18 of seconds. As a reminder, our retina is made, among others, of photoreceptors : 5 million of cone cells (day time and colorised vision) and 120 million of rod cells (night-time and black and white vision).

Picture of Che Guevara that shows the retinal persistance

There are two types of retinal persistence

  • The positive persistence: After having fixed a precise point on an image, the retina registers its color and we can still see this picture during approximately 50ms even with our eyes closed.

  • The negative persistence: It is the result of a prolonged exposure to a strong light intensity which damages the rod cells. Hence, a print of the image remains in the vision for a few seconds. This is what you feel when you stare at the sun for example.
wall of holographic fans showing racing cars

The illusion of movement

In the early 20th century, the retinal persistence has been a source of debates linked to the rise of cinema. For several decades, we thought that it was thanks to this retinal persistence phenomenon that we were able to watch films. According to this theory, a movie is a succession of fixed images. The retina keeps the fixed images in its memory during some milliseconds and it creates a feeling of movement between each fixed image.

This theory has since been refuted by researchers because the movement is still perceptible even with a frequency of only 5 images per second. With such a frequency, we should only see a succession of fixed images because the retina saves an image only for approximately 50ms. Thus, we can conclude that the brain interprets the images and it imagines the movement, it is not just an optical mechanism.

It is actually another phenomenon that is responsible for the illusion of movement in cinema: the beta effect. It is a basic optical effect: the succession of two similar pictures with a different position gives the sensation of a movement between the images. It is an alternative to the retinal persistence.

What is the link with the holograms ?

The retinal persistence phenomenon may have been a source of debates in the field of cinema, but for sure, it is essential for the functioning of our holographic fans because it is the condition to create a floating 3D image.

Whatever the style of the holographic fan, they all work in the same way. We can find LEDs strips on each blade of the fan. They all are switched on at the same time, synchronised with the video saved in the device while the fan starts its high-speed rotation movement. Finally, it is the combination of the LEDs light and the rotation of the fan that creates the hologram.

Nevertheless, the holographic fans aren’t hologram projectors ! As a reminder, there is no existing technology that can create a free floating image without any projector. Our holographic fans offer a clear image and when it moves, the fan is almost invisible. The brightness of our fans is about 1800cs/m² which enables you to use it day and night.

The holographic fan technology does not stop there ! It is also possible to synchronise several fans together in order to create a larger hologram and even 3D human-sized animations !

To conclude...

We saw that the retinal persistence is a way to create the illusion of a movement thanks to the memory of the retina cells. Doing so, it offers many possibilities for the audiovisual field and especially for holograms. The holographic fan is the best holographic device to use this phenomenon. All of our holographic fans display high-quality holograms with an almost invisible support. Hence, it makes it, at the present time, the closest thing to the holograms that can be seen in science fiction films !