a high gain transistor with a IR -receiver (led) ? where the diode is reversed biased from collector to base of the transistor? if yes, then would there be any limitations?
A photo-diode would be better than an LED used as a makeshift photodiode. You'd still have to amplify it though, I'd use an opamp rather than a transistor amp. CDS photocells can be used as well depending on exactly what you need this for. A little more detail would be nice.