In 1907 English engineer Henry Joseph Round was testing the rectifying current behaviour of SiC crystallites and noticed that a faint yellow light was emitted from the SiC; this was simultaneously the first reported observation of the phenomena of electroluminescence spectroscopy and the first successful operation of a light emitting diode (LED). The work of Round was expanded on by a few others in the early 20th century, but it would take many decades for LEDs to become efficient enough for practical use.