Some technologies seem to get to within a year or two of being serious, and staying a year or two away forever. I remember a stretch of the 1980s where five successive years were "The Year Ethernet Will Finally Take Off", and I must have written the story about "fuel cells powering mobile phones next year" four or five times in the past decade. And now we have plastic light-emitting diodes: lumps of organic material that you can mix up like any other plastic, but that glow when you put a voltage across them just like the ordinary LEDs that have to be made in huge expensive semiconductor fabrication plants. The advantages are obvious: cheap, flexible and easy to make, organic LEDs (OLEDs) are going to be big. Everyone knows that. But when? OLEDs have been burning away merrily in the labs for a few years now. Cambridge Display Technology, one of the inventors of the basic technology, has just bought Oxford rival Opsys and the chief executive is confidently predicting we'll have full-colour screens rivalling LCD flat panels by 2005. Well, yes. We were going to have something like that three years ago, once a few small problems were ironed out -- contamination leaking in and giving them very short lifetimes, I seem to remember. The contamination problem is fixed now, and everyone's moved on to the next issue. This time, the big showstopper is differential ageing: red, green and blue OLEDs fade over time, but at different rates. What looks like a crisp, well-balanced image at manufacture acquires a curious hue after a few months, or so I'm told. It's fixable, given time, and all you can say is that when it is, the next set of problems will come to the fore. Eventually, the product will be good enough to ship, flaws and all: nothing's ever perfect. Even the cathode ray tube is being tweaked, a hundred years after its birth. But until the point that you can sell what you have, the financiers have to be kept happy -- and that means they have to believe they'll start getting their money back within a reasonable frame. Something like, oh, two years? And thus, this acquisition is a good opportunity to say to the money people, "See? Progress! Just a little longer, and we'll all be in clover." And the best way to say something to the capitalists is to put it in a press release and tell the world -- which is why everything is two years away, all the time. Of course, at some point this will be true. But I don't know that'll it'll be in two years' time, and neither does Cambridge Display Technology.