This sensor is based on arduino - LED sensor example with an IR LED used as ir emitter. I do 2 readings: one with ir emitter on - one with ir emitter off If the result of this operation is positive, we have something in front of the sensor. With this algorithm I can determine also the ambient light. Look at the code.
http://www.gioblu.com/index.php?option=com_content&view=article&id=59:sensore-prossimita-led&catid=37:sensori&Itemid=18 The google translate traduction is not precise.