Persistence of Vision - Physics Demonstrations - Persistence of Vision | Physics Undergraduate Labs

Strobe lights can trigger seizures in individuals with photosensitive epilepsy (approximately 1 in 4000 people). Always announce the use of strobe lighting before beginning the demonstration and allow any affected students to look away or leave if needed. Avoid prolonged exposure and keep strobe frequencies away from the critical 15-25 Hz range when possible.

Purpose

Demonstrates persistence of vision and the stroboscopic effect using rotating patterned disks illuminated by a strobe light. Students observe how discrete images merge into continuous motion or appear frozen, illustrating the temporal resolution limits of human vision.

Motorized rotator unit with white base holding a white disk showing a bird outline and red shape. Eight interchangeable white disks with various black geometric patterns (radial lines, dots, spokes, spirals) are displayed in front.

Bird-and-cage disk under blue strobe illumination, showing the black bird outline and red teardrop shape appearing to overlap on the spinning disk

Spinning disk under blue strobe showing a radial spoke pattern with visible motion blur; red power indicator light at base of rotator

Spinning disk under blue strobe showing a different spoke pattern with more pronounced motion blur creating a flower-like appearance

Spinning disk under blue strobe showing radial lines blurred into a smooth continuous appearance with faint spoke shadows

Spinning disk under blue strobe showing many radial lines blurred into a dense spoke pattern with slight motion blur

Figure 1: Motorized rotator with the bird-and-cage disk mounted, and the full collection of interchangeable illusion disks.

Figure 2: Bird-and-cage disk under strobe illumination. When spinning, the two images on opposite sides merge so the bird appears inside the cage.

Figure 3: Radial spoke pattern under strobe illumination with partial motion blur — the strobe frequency is not quite matched to the rotation speed.

Figure 4: A different strobe-to-rotation frequency ratio produces a more blurred pattern with apparent rotational symmetry.

Figure 5: At higher rotation speed relative to strobe frequency, persistence of vision smooths the radial lines into a nearly continuous pattern.

Figure 6: Dense radial pattern under strobe illumination showing nearly frozen spokes with slight residual blur from speed mismatch.

Safety Warnings

Warning: Photosensitive Seizure Warning

Purpose