Still, LG's current passive sets now do 1080i 3D thanks to a firmware update so I assume the 55LM9600 should follow suit right out of the box.

LG has now made some improvements to the TVs with Cinema 3D and all current users and future users will benefit from this update as it is a firmware update to the TV. LG says that they have changed the algorithm used to show 3D pictures.

Before the Cinema 3D technology worked like this: During a time period of 1/200 seconds the TV showed 2 frames; 540 lines for the left eye and 540 lines for the right eye.
The new algorithm shows 4 frames instead of 2 during the 1/200 second time frame. It shows 1080i for the left eye and 1080i for the right eye.

When these are combined the two pictures create a 1080p picture according to LG. LG believes that this update improves picture quality on their Cinema 3D TVs to compete directly with the active 3D TVs such as 3D plasma TVs. You need to turn off TruMotion to utilize the new algorithm. See the illustration below.

LG claims that its FPR panels are actually displaying all 1080 lines of information for each eye, but not at the same time. In the first 120th of a second, the odd lines of the left image are displayed in the odd lines on the screen and the odd lines of the right image are displayed in the even lines on the screen. Then, in the next 120th of a second, the even lines of the left image are displayed in the odd lines on the screen and the even lines of the right image are displayed in the even lines on the screen."

"However, this puts some lines in the wrong place—even lines from the image in odd lines on the screen and vice versa—which would cause a slight but noticeable vertical judder. And even though all 1080 lines of information for each eye are being displayed, each eye sees only 540 lines of resolution at any given instant. Not only that, objects behind or in front of the screen plane will exhibit interlace artifacts.