A dealer has been telling me how exasperated he is by the contradictory advice he keeps getting on 3D. Only one company, Panasonic, has been offering tech briefings with people who know what they are talking about. Most manufacturers want just to preach to reviewers or talk superficially to tabloids who will give them a quick five-star puff. They duck serious questions or take an age to give garbled and inadequate answers.

So here are a few key basics. It may sound like a truism, but it seems some manufacturers’ sales staff need reminding that to display 3D you need a 3D TV. And there are two very different kinds.

Passive polarising sets (from LG, JVC and Hyundai) have a mesh of near-invisible filter strips over the screen, and are viewed with passive polarising glasses. Sky pubs use these sets largely because the glasses are cheap and it does not much matter if footie fans steal them.

The downside is that because the display interlaces the left and right HD images, each eye only gets Half HD.

The active plasma TVs sold by Panasonic display a very rapid stream of left and right HD images and the viewer wears glasses with shutters that rapidly blank the left and right eyes. So each eye gets Full HD. But the glasses are expensive, £100 a pop, so they’re not really practical for pubs.

Panasonic claims that only plasma screens can switch the left and right images fast enough for blur-free 3D. Rivals Philips, Sony and Samsung say they can do it just as well with LCD screens. We won't know who is right until given the opportunity to see the same 3D movie material side by side on a plasma and an LCD TV.

Shutter switching is controlled by an infra-red link between the TV and glasses. Different sets use different switching signals. So the glasses for one brand will not work with a TV of another brand.

3D sets need HDMI Ver 1.4 connectors, too, to handle the 3D signal correctly. Existing 2D sets don't have HDMI 1.4 and don't have any mechanism for controlling shutter glasses. So they can't display active shutter 3D.

Existing 2D sets don't have a mesh of polarising filters over the screen, so the suggestion, apparently made by one company salesman recently, that they can display 3D when viewed with polarising glasses, is just plan daft.

The next big area of confusion will be how different types of 3D TV cope with the 3D output from a new 3D Blu-ray player. More on that next week.

Barry Fox