Complex sentence: In some later experiments with cat's whisker detectors using a variety of substances, he passed current through them and noticed that some gave off light-the first known report of the effect of the light-emitting diode.
Split into simpler sentences: In some later experiments with cat's whisker detectors using a variety of substances, he passed current through them and noticed that some actually gave off light-the first time a light-emitting diode had been seen. This is the first known report of the effect of the light-emitting diode.