The anti-gravity fountain lamp is a table decoration and a light source, which creates an anti-gravity illusion with falling water. The base and the upper part of the fountain are connected by four aluminum rods. The fountain comes with two opposing glasses, one attached to the upper part and the other to the lower part, giving it an hourglass appearance. In addition, it also has some practical value, showing the right time and purifying the air. Negatively charged air molecules, which are generated at the bottom of the fountain lamp, help clean the air in the room by combining, for example, dust particles and bacteria. By filling the tank with water and turning on the small pump, it starts circulating water droplets through a hose inside an aluminum tube. But why does it seem to us that the water droplets in the center of the fountain are levitating and moving upwards, even though there is no pipe in there?
The anti-gravity effect created by the water fountain lamp is an optical illusion. By flashing the LED lights at a frequency close to the frequency with which the water droplets are pumped out, a stroboscopic effect is created, and it appears to us that the water droplets are levitating or even moving upwards.
What is the stroboscopic effect, and how does it work?
A stroboscopic effect is created when a light pulsating at a certain frequency illuminates some periodic motion. For example, it could be a rotary motion like an airplane propeller or any other cyclical motion, like the waving of our hands or the falling drops of water in our anti-gravity fountain lamp. You have probably noticed that when you watch videos on TV or YouTube where you can see spinning wheels or propellers, they sometimes seem to be moving in reverse. It is also a stroboscopic effect and occurs because the periodic movement of the wheel or propeller is filmed at a certain speed (a certain number of frames per second). The picture below illustrates how such an illusion is created in the video.
For example, suppose a camera is filming a rotating propeller at 24 frames per second. That means it takes 24 pictures every second. When the propeller rotates exactly 24 revolutions per second, it appears stationary in the video. That is because, at the exact moment when the camera takes a picture, the propeller is back in the same position as in the previous image.
Now let's see what happens if the propeller rotates at a slightly slower speed and makes, for example, 23 revolutions in one second, but the camera still films at 24 frames per second. In this case, at every moment when the camera takes a picture, the propeller has gone through a smaller rotation angle and has not completed a full rotation. Therefore, it seems to us from the video that the propeller is rotating in the opposite direction.
How do strobe lights create an anti-gravity effect with falling water droplets?
Now let's go back to our anti-gravity fountain lamp. The illusion of water droplets moving upwards is created here in a very similar way. Instead of a camera that takes pictures, we now have fast-blinking LED lights that illuminate the falling water droplets. The pump circulates the water and creates a steady flow of water droplets in the fountain. If the pump circulates the water at the same frequency as the lights that illuminate the falling water droplets, then it seems that the water drops are standing in the air or levitating.
For example, suppose the pump operates at a frequency of 50 Hz. Every second, 50 drops of water fall from the top of the fountain lamp. In the upper picture, I have marked one drop of water in red so that it is better to see where it has fallen in a fraction of a second. In fact, of course, they are all very similar, and we do not differentiate between them. If the LED lights illuminate the falling water droplets with the same frequency (50Hz) with which the water droplets are produced, then every next water droplet has reached the place where the previous water droplet was 1/50 of a second ago by the moment of illumination. So it seems to us that the water droplets are levitating in the air.
However, if the water droplets are produced at a lower rate or the LED flashes with a higher frequency, then it seems that the water droplets are moving upwards in the anti-gravity fountain. Let's say, for example, that the pump produces 45 drops of water per second, but the LED flashes at a frequency of 50 Hz. In such a case, the LED illuminates the water droplets at the moment when the water droplet has not reached the place where the previous water droplet was, at the moment of the previous lightning.
The upper image illustrates a situation where it appears to us that the water is moving upwards in an anti-gravity fountain. I have again marked one water droplet in red so that it would be better to understand where it has reached in a fraction of a second. At moments A, B, and C, the LED lights up and illuminates the water droplets. As you can see, the situation is very similar to the propeller example, where the camera was shooting a rotating propeller. The propeller rotation frequency was a little slower than the rate at which the camera was taking pictures, and it seemed to us that the propeller was moving backward.
Finally, here is one very good website I found (JF Fountain from instructables.com), where you can find a tutorial on how to make yourself an anti-gravity fountain using some simple components and an Arduino board.