Context: A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semi-conductor under the influence of an electric field. The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.

Question: What converts absorbed light energy into an electric current?
Answer: P-N junction

Question: What is the phenomenon where a P-N junction emits light when an electrical current is applied to it?
Answer: electroluminescence

Question: Where are the free electrons located in the production of electroluminescence?
Answer: the conduction band

Question: Whose energy levels are lower than the electrons in the electroluminescence process?
Answer: holes existing in the P-region

Question: Why is some energy in the electroluminescence process emitted as heat and light?
Answer: to recombine the electrons and the holes

Question: What converts absorbed light energy into an non-electric current?
Answer: Unanswerable

Question: What is the phenomenon where a P-N junction emits light when a non-electrical current is applied to it?
Answer: Unanswerable

Question:  Where are the free electrons located in the production of non-electroluminescence?
Answer: Unanswerable

Question: Whose energy levels are lower than the non-electrons in the electroluminescence process?
Answer: Unanswerable

Question: Why is some energy in the electroluminescence process emitted as heat and darkness?
Answer: Unanswerable