Question: state the basic operating principle of an led
[{'answer': 'Electroluminescence', 'provenance': [{'wikipedia_id': '18290', 'title': 'Light-emitting diode', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 19, 'bleu_score': 1.0, 'section': 'Section::::History.:Discoveries and early devices.\n'}]}]