As the infrared light-emitting diodes, it emits 1 ~ 3μm of infrared light, the naked eye can not see. Usually only a single infrared light emitting diode power is only a few mW, different models of infrared LED luminous intensity distribution angle is not the same. Infrared LED forward voltage drop is generally 1.3 ~ 2.5V. Because of the infrared light emitted by the human eye can not see, so the use of the visible LED detection method can only determine the PN junction positive, reverse electrical characteristics are normal, and can not determine the normal light-emitting situation. To this end, it is best to prepare a photosensitive device (such as 2CR, 2DR type silicon photovoltaic cells) as a receiver. With the multimeter metering battery voltage changes at both ends of the situation. To determine whether the infrared LED with the appropriate forward current after the launch of infrared light.