Ardunio + motion sensor leds

Hi I was hoping that you guys could help me out. I will be making a beer pong table in the next couple of weeks and I want to have motion sensor led lights that will light up when a cup it placed on the table. So when all ten cups are aligned on the table there will be 10 led lights on and when a cup is removed the light will go off. So what I need to know is how can i accomplish this? Should i use photocells or would ir sensors be better for this application. If you could help me out with the programing too that would be great. Thanks

If a light lights up under a cup how will you see it? Also remember that glass blocks IR.