gr8 question..... hey wt i think is dat we knw dat both tube light and d comp screen doesnt emit light in a continuous manner... d rate of of FLASHING sd light( if i may say so)... is faster in case of a tube light dan a comp screen... moreover d screen in a comp shows pictures in a slide format running from top 2 bottom so wen we move our hands fastly infront of it we see as iff dey r like captures and not a continuous movement....!!!!!!