This friend is hypermetropic, and uses reading glasses. He doesn't have major issues facing car headlights, or using a torch (the one with a bulb - not a white LED). Yet place him in front of a TV/Computer screen, and he'll develop an ache in the eye sockets in no time.
I understand an electric torch, an incandescent bulb, a car lamp are all DC types, whereas a TV/Computer screen is fast changing AC.
Are human eyes equally sensitive to light from an AC, and a DC lamp?