Modern LEDs light up with incredibly low currents. In a RF noisy environment, I've often seen LEDs glow just by touching one side with a wire and the other to g

Modern LEDs light up with incredibly low currents. In a RF noisy environment, I've often seen LEDs glow just by touching one side with a wire and the other to ground. Just the parasitic from such a crude antenna was enough. Of course as stated by another comment, our eyes are also incredible, and can pick up very faint amount of light.