Everyone can see the flashing. You can become aware with a bit of effort.
Find a LED light that isn't on a continuous DC power supply. Christmas lights work well for this.
Pick two objects, one far to the left of the light, one far to the right. Focus on one side, while making sure the other object and the light remain in your field of view. Next, glance at the second object so your eyes quickly travel across the LED.
If you have christmas lights you can exaggerate the effect by spinning the cable. You don't need to move your eyes at all in that case.
If you have manual control over the shutter speed on a smartphone or other electronic rolling shutter camera, just turn the shutter speed high. It's possible to detect flicker up to at least a few kHz this way.
Find a LED light that isn't on a continuous DC power supply. Christmas lights work well for this.
Pick two objects, one far to the left of the light, one far to the right. Focus on one side, while making sure the other object and the light remain in your field of view. Next, glance at the second object so your eyes quickly travel across the LED.
If you have christmas lights you can exaggerate the effect by spinning the cable. You don't need to move your eyes at all in that case.