Actually, the PS4's DualShock 4 light can be turned off
Yesterday, it was reported that the lightbar on the top of the DualShock 4 controller does not, and could not, be turned off by the player. As it turns out, the LED light can be turned off -- or disabled, rather -- but only if a developer so chooses.
When asked on Twitter, "Can games developers choose to turn the light off on the DS4?" Sony Worldwide Studios president Shuhei Yoshida clarified, "yes."
While the light personally wouldn't have affected me, there was some concern that the light could cause a reflection in glossy TV screens, especially when playing a game in the dark.
So while the player does not have the option to do so, developers can best judge if it's needed. As it stands right now, the lightbar was meant to be used alongside the PS Eye, but that was back when the camera was included with the PS4. It still is designed with the camera in mind, but with Sony's decision to no longer bundle the Eye in with the PS4 system, the lightbar kind of took a backseat to the rest of the DualShock 4's features. The lightbar still has its uses, though. In Killzone: Shadow Fall, for instance, the LED light will be used to represent the player's health.