We describe the use of a low cost light emitting diode (LED) as a single photon detector. The LED is operated under reverse bias conditions, and produces a measurable pulse of current for every photon detected. The analog current signal is converted into a digital pulse using a standard comparator circuit. A high voltage summing amplifier is used to apply the reverse bias. These analog circuits are controlled using a custom LabVIEW software, which allows us to measure the count rate as a function of bias voltage. Preliminary experiments show that a threshold voltage of approximately 22 - 23 V is necessary to obtain a measurable count rate. We find that this threshold depends on the wavelength and intensity of light incident on the LED. A systematic study of this dependence is currently underway. The reverse biased LED together with our analog circuits can also be combined with standard pulse counting modules. This allows us to measure the distribution of pulse heights as well as their arrival times. These distributions provide additional insight into the behavior of a reverse biased LED.
