But limitations abound. For one, the parallax barrier in devices that have a 2-D/3-D option is usually a second LCD screen placed atop the standard, 2-D display (this is how the 3DS works). Two screens eat up more power, plus the rear screen must operate at higher brightness to compensate for all of the light being blocked by the barrier, cutting battery life in half (or sucking more power from the wall). The vertical barrier also restricts viewing angles and doesn't allow for multiple perspectives. If you're not sitting more or less in front of the screen, the 3-D illusion collapses. For portable devices like the 3DS where the screen might be rotated or tilted, this is particularly problematic.