   Screen & phototransistor
  I want to detect when an area of my notebook display goes from dark to white by placing a phototransitor focused on the area tight against the screen and metering the output.  When I perform the experiment I get no voltage change on the phototransitor when I go from dark to light.  If I shine a flashlight on the phototransistor I get a voltage as expected.  The phototransistor is a NTE3037 which is rated white light.  I know that notebook screen displays are driven on and off.  Even so I would expect some voltage.  Any ideas?   