When the QTI sensor is over a dark surface, the reflectivity is very low; when the QTI is over a light surface, the reflectivity is very high and will cause a different reading from the sensor.
The IR Distance Adapter is designed to interface the Sharp GP2D12 sensor to the PhidgetInterfaceKit 8/8/8 or the PhidgetTextLCD.
The Sharp line of analog infrared rangefinders are back, and with their usual high-level of noise and color immunity. These are great distance sensors that should be near the top of anybody's list for simple & effective obstacle detection!
The QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 0.5" x 0.3" module that can be mounted almost anywhere and is great for edge detection and line following applications. This sensor is sold in packs of two units.