100W bulb vs 13" screen
Physics would suggest the irradiance on the retina (W/m^2) as a function of wavelength would be the deciding factor for disease. A 100W bulb at at 30cm covers a much smaller solid angle in the field of view than my laptop screen at normal distance (some ten times smaller according to my BotE (back of the envelope) calculations. Assuming an incandescent light bulb, and assuming LEDs are ten times more efficient than an incandescent light, this suggests the power draw of the screen would need to be 100W to deliver the same irradiance on the retina (albeit over a larger surface area). Given the 58 Wh capacity of my old laptop battery, I would drain it in roughly 35 minutes assuming the processor, memory and disk have no power draw at all.
I think I can safely say the irradiance on the retina is at least one, if not two orders of magnitude lower, as I know too well after replacing a 100W equivalent lamp, and it turned out some joker had flipped the switch to the "on" position while I was doing it. Having such a bright light popping on at about 10" from your face is not fun at all. Watching my laptop screen is not a problem at all.