An optical analyzer includes a light emitting diode (LED). The LED has a body pervious to light and a PN junction semiconductor. The body has a surface portion where a primary light emitted from semiconductor is divided into a first light and a second light. The first light is reflected at a sample and then received by a first detector, while the second light is detected by a second detector. An optical property of the sample is determined by the use of outputs of the first and second detectors.