(5 minutes or less)
No assembly is required for the digital radio, circuit tester, or neon glow lamp; just plug them in and observe them from a few feet away.
A simple source for a neon glow lamp is a button-type nightlight. These are small orange night-lights advertised as 1/4 watt bulbs. They do not have a regular replaceable small lighibulb. Plug the nightlight into the wall or into an extension cord that is plugged in.
(5 minutes or more)
Observe the light source from 3 to 10 feet (90 to 300 cm) away and give it the "Bronx cheer." (A Bronx cheer, also known as a "raspberry," is a rude noise made by blowing air through your lips in a way that makes them vibrate.) Notice that the light seems to wiggle back and forth and flicker. Try shaking your head rapidly and notice whether the light still flickers. See if you can find other body motions that make the light flicker. Try the Bronx cheer on other light sources, such as incandescent lightbulbs. Notice whether the light flickers.
No part of the LEDs or the neon glow tube move when you give the Bronx cheer. Instead, your whole body is vibrating, including your eyes. you can feel this vibration by putting your hand on your head as you blow. The LEDs flash on and off sixty times a second (a neon glow tube glows on and off 120 times a second). This flashing is so fast that your eyes normally can't separate the "blinks." But when your body is vibrating, your eyes are in a different position each time the bulb flashes. As the image of the bulb traces a path across your eyes, it looks like the bulb is moving and flickering. An incandescent bulb won't flicker when you give the Bronx cheer, because the bulb doesn't flash on and off. Incandescent bulbs give a steady glow.
Plug a commercial neon night-light into an extension cord. Tape it firmly in place. Twirl the light around in a circle. (Be careful not to let it hit anything.) Notice that you can see the light flashing. Since the light is moving, it's in a new position each time it flashes. The light traces a path across your eye, and its flashes become spread out and visible. Find an oscilloscope and set it up so that the beam goes straight across the middle of the screen in about 1/1ooth of a second. Ask a couple of friends to stand back a few yards from the scope. Tell them that the oscilloscope is an eating detector. Have your friends watch the scope at the same time. Have one of them eat a peanut and the other one not eat. The person eating the peanut will see the beam jump up and down. Eating causes vibrations of your skull, including vibrations of your eyes. If your eyes are moving, the dot of light scanning across the oscilloscope shines on different parts of your eyes and appears to jump around.