2D Tracking of an object - which sensor?


I'm currently working on a project for which I require a sensor. I've made a quick and simplified drawing of what the result is supposed to do: http://i.imgur.com/ti83rzJ.jpg . Basically I want one LED of a LED-Strip to light up dependent on the location of a moving object. If the object in above image (say a slow rolling ball) were to move from bottom to top the LED strip should also light up from bottom to top. I have no problem getting the LED strip to light up adequately, however I'm not sure which sensor actually can pick up objects as required in this case. As I've understood regular IR sensors can only detect IF there is an object and how far it is away, however they can't pick up said objects relative position on the y-axis. Is there any way to do this rather easily, perhaps with triangulation? I've looked into Bluetooth and RFID but haven't found anything particularly useful.

Thank you very much in forward!

The [http://cmucam.org/projects/cmucam5]Pixy (CMUCam5)[/url] is an Arduino-compatible camera that can track colored objects.

Edit: fixed link.

Thanks for your quick reply! I've been looking into the Pixy, it looks really good but sadly is a little too expensive for my projects budget. Do you think it would be feasible to recreate a more basic version of the Pixy by myself, similar to what this person did Arduino Computer Vision | Project Lab ? I have worked with openCV in a java project before, never anything like this on Arduino though.

Arduino does not have the memory or speed to process images.

The Pixy is well worth $75, unless your time is worth more than about $0.10/hr.

You could rotate a direction-sensitive sensor and make it follow (lock onto) the object, once it has detected the object. This way you'll get at least the angle to the object. An IR sensor may do that, with a tube on the receiver to make it directional.

Or use a US sender with two receivers, and do some triangulation.