Hello, I'm a student in the faculty of Engineering, and we have a project for making a garage door system:(a sensor at the door which sends to a parallel port using a signal conditioning circuit a signal when a car is entering, this signal goes to the PC... )
All I want to know what type of light sensor should I use (it's a design project (just a case study))

If you can break a light beam with the car, use infrared (inexpensive, simple). If you can't, use RFID transmitters and sensors.

Or else, you can use a proximity sensor... teknic uchenar make... with a relay to give input to your PC.