To produce visible light, an LED must have a band gap lying in which of the following ranges?

0.1 eV to 0.4 eV
0.5 eV to 0.8 eV
0.9 eV to 1.6 eV
1.7 eV to 3.0 eV

Correct answer: 1.7 eV to 3.0 eV

Solution

Visible light spans roughly 1.8 to 3.1 eV in photon energy, so an LED emitting visible light needs a band gap of about 1.7 to 3.0 eV.

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