Q.The light emitted in an LED is due to

An LED is a p-n junction diode that emits visible or invisible light when FORWARD biased -- electrical energy converts directly to light energy, a process called electroluminescence. Forward bias drives electrons and holes to diffuse across the junction and recombine; each recombination releases energy either as heat (non-radiative) or, in LED materials, as a photon of energy $h\nu\approx E_g$ (radiative). The band gap $E_g$ of the chosen material therefore fixes the emitted colour: SiC gives blue, AlGaP green, GaAsP red, and GaInN white. For example, GaAsP with $E_g=1.875$ eV gives $\lambda=hc/E_g\ …